Chapter 21. Other Digital Audio Devices

Digital radio, using Eureka-3 digital audio broadcasting (DAB), is now up and running, although receiver prices are high, and the emphasis so far has been on in-car units rather than home units. There are, however, several other digital options that have now opened out for audiophiles, particularly for those with computing interests. The problem might be that, with so many options either available or promised, no one can really decide what to buy until the situation settles.

21.1. Video Recorders

At the time when Beta and VHS video recorders where competing for the United Kingdom market, several makes of Beta recorders, notably Sanyo, offered the option of sound recording by digitizing an audio input and recording it as if it were a video signal. These recorders have become prized possessions of some audiophiles because of their good sound recording quality and low-cost media. That’s assuming they can still get hold of Beta tapes, which, although now rare in the United Kingdom, are still easily available in other parts of the world and are still manufactured for the professional grade of Betamax camcorders.

Looking at more modern equipment, manufacturers such as Hitachi have incorporated audio facilities (including audio dubbing) into Nicam recorders. The input audio signals are converted to Nicam stereo digital format, which implies some compression and recorded. This offers at least 3 h of good-quality music on a standard El 80 tape. One drawback is that automatic gain control settings often result in rather low-level recording so that you need to adjust your volume control settings on replay.

21.2. High Definition Compatible Digital (HDCD)

High Definition Compatible Digital (HDCD) is one of several recent improvements in the coding of the familiar compact disc. HDCD discs, developed by Pacific Microsomes, are created using a faster sampling rate of 96 kHz, as compared to the conventional 44.1 kHz used on present CDs, and with 20-bit data units. If this were coded directly on to the CD it would not be compatible with existing CDs, so data are compressed to 16-bit units and a 44.1-kHz pulse rate.

The result is that the HDCD discs can be played on a normal CD deck, but these discs will deliver more dynamic range and overall better sound on a player that uses HDCD decoding. Discs prepared in this way can be recognized by the use of a distinctive HDCD logo.

The first firms to offer players with HDCD capability were Denon, Harman Kardon, Rotel, and Toshiba. Although more than 4000 titles are available in the United States at the time of this writing, these and HDCD players are not easy to find in the United Kingdom (one of the recent offerings is from the respected firm of Linn). The players contain interpolation circuitry that can also enhance conventional CDs, and HDCD has, as you would expect, arrived mainly on the players in the £1000 upwards price bracket. Players indicate the presence of an HDCD disc by lighting an indicator. Note that the most recent Philips CD recorder caters to copying HDCD discs.

21.3. CD Writers

CD writer drives have become commonplace on PC computers where they are used primarily for making backup copies of valuable data and programs, but they are still a fairly rare sight on hi-fi installations. The CD writer drives as used in computers have several advantages:

1. They are considerably less expensive.
2. They allow you to store computer data, including still or moving images, as well as sound.
3. They are compact, fitting into a 5¼-inch drive space.
4. You can decide for yourself what software to use with them.
5. They can use either write-once (CD-R) or read-rewrite (CD-RW) discs.
6. They can make recordings at a higher speed than music can be played.

If you do not have a suitable computer, of course, this option is not open to you, and you will need to look at one of the CD writer units intended to be used along with a hi-fi system. Such units are more expensive because they need to incorporate several items of circuitry and software that would be available within the computer. In this chapter, the term drive refers to a unit incorporated into, or connected to, a computer, and deck means a unit that is part of a hi-fi stack or assembly.

Until 1990, the idea of creating your own CDs would have been considered ridiculous because the creation of a CD involved many processes that called for elaborate and expensive equipment. The availability of compact disc writing equipment that is well within a normal domestic budget is due to evolution of CD technology, dispensing with the need to burn into the disc material. The system that is mainly used for home sound recording, or for computer use, is CD-R, meaning CD recordable. This system allows you to write once to a disc and read it as many times as you like. Early versions also allowed this, but later technology allows you to add more tracks to a disc if you did not fill it on earlier sessions. A disc that permits this type of use is described as multisession. At the time of writing, a blank CD-R disc costs around £0.75, making this the least expensive method of recording that has ever been devised. A CD-R disc will hold up to 74 min of full CD-quality music, or the equivalent in computer data, about 650 Mbytes.

Computers and some more recent hi-fi CD recording decks can also use a different form of technology, CD-RW, which allows a disc to be recorded, played, wiped, and recorded again, much like as you reuse a tape or a floppy disc. This technology is, at present, not so well suited to audio use, and although the blank discs that once cost around £10 each are down to less than £3 each, they are not so popular for computing use either. Many of the better computer CD writer drives can use either type of disc, and prices are remarkably low, typically £125 if you shop around. Most CD-R drives can write at 2× or 4×, or even 6×, depending on the model, which means that they can make a recording of existing digital files faster than a tape. A 2× recorder will record at twice the speed at which the music can be played. This is an advantage for the drive in a computer, because data files of music can be processed as fast as the CD writer allows, but for the CD-writer drive in a hi-fi installation you cannot speed up the music at the input and high recording speed is pointless. A drive or deck that allows both CD-R and CD-RW discs to be recorded and replayed is known as a CD-R/RW drive or deck.

Unlike DAT, there are no copyright barriers to CD recording. DAT developed as a medium for sound recording, and the record industry worked overtime to make sure that the system was not released until it incorporated safeguards that prevented serial copying. This so hindered the acceptance of DAT that it never became widely used, certainly not in Europe. In contrast, the writeable CD was developed as a computer peripheral, and the record industry did not realize what was happening until it was too late to stop it. Compared to DAT, CD recording is fast, inexpensive, and easy, with no hindrance to making copies. Copyright protection has, however, been developed for DVD (see 21.9 DVD).

To understand how the change in technology has come about, think back to how the early CDs were manufactured, and are still manufactured. The CDs that you buy are made by burning indentations with a powerful laser into the track surfaces of a master disc, using the presence or absence of a pit to indicate a 1 or 0 digital bit. The player also uses a laser, operating at a much lower power level and aimed at the track. The amount of light that is reflected from the laser beam depends on whether the beam hits a pit or an unpitted piece of track. As the disc spins, these changes in intensity are detected and converted into electrical signals, duplicating perfectly the digital signals that were used to create the original. The advantage of this system is that it permits record pressing analogous to the old vinyl disc method. The CD that is burned by the recording laser is used as a master to make copies that can be used for stamping out plastic discs with the information intact.

This process, incidentally, is much less expensive than the method of recording tapes, which need to be recorded from one end to the other, albeit at a faster speed than they are played. It follows then that a CD is much less expensive to produce than a tape, and some bargain CDs, even in the United Kingdom, are sold at prices that reflect the lower cost. The majority of issues, however, maintain the “CD premium” in prices, in the belief that buyers will pay more for them even if they have cost less to make. You may have noticed the low prices of magazines that have CDs attached, pointing out the low price that the magazine has paid for the CD.

The more modern CD-R drives are recorded using a low-power laser that does not burn pits into the plastic of the disc. Instead, the discs are coated with a dye that is affected by the intense light from the laser. The effect is to change the dye color and, although the change is not a vast one, it can be seen by the eye. If you look at a partly recorded CD-R disc, you can see that the recorded portion (the inner part) is a quite distinctly lighter shade of blue (usually) than the outer unrecorded portion. Because this change is irreversible, the disc tracks can be written only once. This type of process is called dye sublimation, and the surface appearance of the disc is also due to a thin metallic coating, silver or gold, to make the surface more reflective. CDs created with CD-Rs are compatible with all other computer CD-ROM drives.

Oddly enough, a “premier price” situation has developed with blank CD-R discs. The requirements for recording computer data are more onerous than for sound recordings; after all, your sound system does not shut down if there is a mistake in a tiny fraction of a musical note. This should mean that any blank CD good enough for data recording should certainly be good enough for audio. Some shops, however, will try to sell audio-grade CD-R blanks at a very substantial premium.

The rapidly growing use of CD-R/RW has spawned a whole set of new terms that are probably better known to computer users than to audio enthusiasts. Some of the more important terms that have not been explained so far are summarized here.

Disc at once (DAO): A CD-R/RW writing mode that requires the whole of the data to be written in one uninterrupted session. Compare track at once, incremental writing.

Finalized disc: A CD-R disc that has had its overall lead-in and lead-out information written so that no further sessions can be recorded.

Fixation: The set of actions used at the end of a writing session on a CD-R drive. Fixation writes lead-in and lead-out information and creates a table of contents for the disc so that the disc can be read on a normal CD-ROM drive or audio CD player. If the option of fixation for append is used, further sessions can be added to the disc until it is full. See also finalized disc.

Incremental writing or packet writing: A method of writing data to a CD-R or CD-RW disc in which several sets of data can be written in each track. This reduces the effect of the overhead of 150 recorded blocks that are used for run-in, run-out and linking.

Lead-in: A section of all CD ROM or music discs, prerecorded, CD-R or CD-RW, that contains information on the data or music contents. The lead-in area immediately precedes the recorded area. For a fully recorded disc, the lead-in contains the table of contents.

Lead-out: A section of all pr-recorded compact discs that follows the recorded area (on the outer rim of a fully recorded disc). On the CD-R or CD-RW discs, the lead-out is not created until the disc is declared as fully recorded (preventing further recording). With no lead-out, the disc cannot be replayed on music players, and some older CD-ROM drives on computers may not accept it.

Multisession: Refers to a CD-ROM that can be recorded more than once, adding new material on the subsequent recording, until the disc is full. All computer CD-ROM drives and most hi-fi CD decks should be capable of playing CDs recorded in this way.

PCA: Program calibration area, the portion of a CD-R disc used for making a trial recording to calibrate the laser intensity needed for the disc that is being used. This allows for differences in disc materials, particularly between CD-R and CD-RW discs.

PMA: Program memory area, the portion of a CD-R or CD-RW disc that contains a table of track numbers along with start and stop data positions for each track.

Session: A recording made on CD-R or CD-RW that can consist of between 1 and 99 tracks. A session is preceded by a lead-in and ended by a lead-out, and a multisession disc is one that can be recorded at different times, writing a complete session on each occasion, with all data readable.

Table of contents: A table of track locations and extents prepared by the CD-R/RW software so that the player can locate each track and data it contains.

Track at once: A system for writing a CD-R or CD-RW disc that writes the session as a set of complete tracks. Compare disc at once.

21.3.1. Uses

The hi-fi version of the CD recorder is used much as you would use a cassette recorder to record music from any other sections of the equipment, such as tuner, cassette deck, vinyl-disc deck, and DAT deck. You may also, subject to the restrictions of equipment and copyright, be able to record from an existing CD player, and this type of transfer is much better if the CD player allows a direct digital output that can be connected to the recorder.

The computer type of CD-R/RW drive must be used along with a sound card that allows line and microphone analogue audio inputs. The quality of recording that you can obtain depends very much on the quality of the analogue-digital conversion in the sound card, and few provide anything like what we accept as CD sound quality. If you are using the system to copy sound tracks from a cassette recorder to a CD, however, the quality level of most cards is acceptable. The line input level of most sound cards is lower than we are accustomed to in hi-fi equipment, and you may need to use the microphone input. This, however, may be too sensitive, causing distortion at high sound levels, and an attenuator may be needed. Some cassette decks allow you to vary the output, which is an ideal way of tackling the problem.

The computer type of drive is well suited to CD copying and to making compilations from a variety of discs. This is not to say that these actions cannot be carried out on the hi-fi type of deck, but you can be certain that the computer type is using direct digital transfers, not converting the CD output into analogue and then converting back to digital in the recorder. The main advantage of using the computer drive is that you can add images, text, and other data into the same CD if you wish (and if you can cope with the mixture). This is particularly useful if you want to make multimedia shows of sound and images.

We shall look at audio and other file transfers for the computer CD-R/RW drives in more detail in the following sections, as many of the steps are almost identical. For the moment, a description of a popular hi-fi CD-recording deck will give you an idea of what is currently “state of the art” in this field.

The Philips CDR 770 (Figure 21.1) was launched in September 1999 and was initially marketed mainly in Germany, where the main demand for CD recorders seems to be at present (as an Internet search will confirm). The initial price in Germany was DM 699, roughly £233, which compares well with earlier models from other manufacturers. The CDR 770 uses the 43.5-cm width that is now standard for hi-fi components. Like any other recorders, the CDR 770 allows consumers to make their own recordings from digital sources, as well as from any analogue sources connected to their audio system.

Figure 21.1. The Philips CDR 770 CD recorder deck.

The CDR 770 performs analogue to digital conversion using the Philips system called DLR (Direct Line Recording). This uses the normal CD 44.1-kHz sampling frequency for bit-by-bit conversion, and for CD copying actions it ensures highly accurate recordings by matching the speed of the recording disc to that of the playing (source) disc. For work with other digital sources, different sampling rates are automatically detected, allowing the CDR 770 to deal with any sampling rate from 11 to 56 kHz.

DLR also allows full bit-by-bit recordings to be made of the new HDCD-encoded discs (see earlier, this chapter). The entire encoding of these discs is therefore reproduced on the copy and is available for playback on compatible CD players with a HDCD decoder.

Audio conversions from other analogue sources are also of high quality using the analogue inputs provided. This makes it easy for the user to transfer LP or older disc collections to CD, as well as to record from other analogue sources such as tapes, radio, or even live music (given suitable microphones).

The CDR 770 also incorporates a CD text function, allowing the consumer to put in text information such as album, artist, or track name. When you make a CD recording using the CDR 770 you can enter your own personal text for each disc, for each track, or for each artist. Each of these text items can contain up to 60 characters. The text is then shown on the display during playback. CD text that is present on prerecorded discs will also be displayed when playing the disc back in a Philips Audio CD-Recorder.

Conscious that the hi-fi user is less accustomed to setting up digital equipment than a computer user, Philips has redesigned the user interface of the CDR 770 so as to make the recording action easier and more intuitive. This uses clear messages at every stage to prevent errors and shows the user exactly what to do next. For example, the new Make CD function allows discs to be recorded and finalized quickly and conveniently, using a single command rather than a set of operations in sequence. Another useful feature is multitrack erase, allowing multiple tracks to be selected and erased at the same time. In addition, the CDR 770 features 99-track programming, easy recording start, an FTD display that gives a clear, at-a-glance indication of the set status, and a music calendar with track bar.

One common problem that users have with hi-fi CD recording is mistaken starts, starting the wrong piece for recording or starting in the wrong place. Because CD-R is a medium that does not allow erasing, this action either makes a set of tracks that you do not want to play or makes the whole disc unusable. This is no problem for the computer user who makes use of a CD-R/RW drive, because the digital files are stored and can be edited before recording, but this is not the way that the hi-fi type of CD recording deck works. Philips has included a buffer memory into the CDR 770, allowing storage of up to 3 s of music.

Table CDR 770 Technical Specifications

Number of channels: 2 (stereo)	Applicable supply: AC 230 V (50/60 Hz)
Power consumption: 15 w	Operating temperature: 5–35°C
Weight: 4 kg	Dimensions: 435×305×88 mm (w×d×h)

Table Audio, General

Frequency response (digital in): 20 Hz−22.05 kHz	Playback S/N: 100 dB
Playback dynamic range: 95 dB	Playback total harmonic distortion: 85 dB (0.0056%)
Recording S/N (analogue): 90 dB	Recording S/N (digital): recording quality equal to source
Recording dynamic range: 92 dB	Recording total harmonic distortion: 85 dB (0.0056%)
Headphones 0–5 V rms / 8–2000 Ω

Table Recording Values for Line Input/Output

Digital coaxial input (direct recording): 12–56 kHz ± 100 ppm

Digital optical input (direct recording): 12–56 kHz ± 100 ppm

Analogue input (level potentiometer): 700 mV rms/50 kΩ=0 dB

Line output voltage: 2 V rms ± 2 dB

Digital coaxial output: 0.5 Vpp/75 Ω

Table Recording Functions, CD-R and CD-RW Discs

Auto start recording per disc	Erase last track (CD-RW disc)
Erase disc (CD-RW disc)	Erase table of contents (for rerecording on finalized RW-disc)
Manual/auto track increment	Remaining recording time display
Autofinalize (make disc compatible to CD player)	SCMS (serial copy management system)
RID code (recorder unique identifier)

Table Playback Functions

Play

Pause

Stop

Direct track selection

Next/Previous track selection

Table Accessories

Search forward/reverse	Remote control (+batteries)
Repeat (all/per track)	Audio cable (×2)
Program play (30 tracks)	Digital coaxial cable (×1)
Time display switching	AC mains cord

The buffer allows a mistakenly started recording to be stopped within the first 3s, before the start of any disc writing actions, and it also ensures that recordings can be made without loss of music at the start of a track when using synchronized CD recording. Buffering also permits the use of synchronized starting from analogue sources. This is done by monitoring the incoming audio signal for the rise in level that indicates the start of play, after which the first few seconds of music are recovered from the buffer for recording.

The recorder incorporates a digital recording level and balance control that allows manual adjustments. This can be used to correct variations between individual discs, a valuable feature if you are making compilations, as it allows you to adjust the volume levels of all tracks. Digital recording level adjustments can be made easily using the Easy Jog control.

The CDR 770 has three sets of input sockets, allowing easy connection to a wide variety of audio sources. Both optical and coaxial digital inputs are provided for the highest quality connection to digital sources, along with standard stereo sockets for connection to virtually all analogue sources, as well as coaxial digital and analogue outputs.

Like its computer drive counterpart, the CDR 770 can make use of both CD-R and CD-RW blanks, and the CD-R discs can be played on any other CD player, either on audio equipment or in a computer system. The CD-RW discs can be replayed on the CDR 770 and on many of the most recent CD playing decks or drives. If your CD player is not of recent design, however, it will not be able to read the CD-RW discs.

21.4. MPEG Systems

When the CD system was launched, following the commercial failure (in the United Kingdom, but not elsewhere) of the earlier laser-disc moving picture system, there was no form of compression of data used. The whole system was designed with a view to recording an hour of music on a disc of reasonable size, and the laser scanning system that was developed from the earlier “silver disc” was quite capable of achieving tight packing of data, sufficient for the needs of audio.

Data compression was, by that time, fairly well developed, but only for computer data, and by the start of the 1980s several systems were in use. Any form of compression for audio use had to be standardized so that it would be as universal as the compact cassette and the CD, and in 1987 the standardizing institutes started to work on a project known as EUREKA, with the aim of developing an algorithm (a procedure for manipulating data) for video and audio compression. This has become the standard known as ISO MPEG Audio Layer-3. The letters MPEG stand for Moving Picture Expert Group, because the main aim of the project was to find a way of tightly compressing digital data that could eventually allow a moving picture to be contained in a CD, even though the CD as used for audio was not of adequate capacity (see 21.9 DVD).

As far as audio signals are concerned, the standard CD system uses 16-bit samples that are recorded at a sampling rate of more than twice the actual audio bandwidth, typically 44 kHz. Without any compression, this requires about 8.8 Mbytes of data per minute of playing time. The MPEG coding system for audio allows this to be compressed by a factor of 12, without losing perceptible sound quality. If a small reduction in quality is allowable, then factors of 24 or more can be used. Even with such high compression ratios the sound quality is still better than can be achieved by reducing either the sampling rate or the number of bits per sample. This is because MPEG operates by what are termed perceptual coding techniques, meaning that the system is based on how the human ear perceives sound.

The MPEG-1 Layer III algorithm is based on removing data relating to frequencies that the human ear cannot cope with. Taking away sounds that you cannot hear will greatly reduce the amount of data required, but the system is lossy, in the sense that the removed data cannot be reinstated. The compression systems used for computer programs, by contrast, cannot be lossy because every data bit is important; there is no unperceived data. Compressing other computer data, notably pictures, can be very lossy, so that the JPEG (Joint Photographic Expert Group) form of compression can achieve even higher compression ratios.

The two features of human hearing that MPEG exploits are its nonlinearity and the adaptive threshold of hearing. The threshold of hearing is defined as the level below which a sound is not heard. This is not a fixed level; it depends on the frequency of the sound and varies even more from one person to another. Maximum sensitivity occurs in the frequency range 2–5 kHz. Whether or not you hear a sound therefore depends on the frequency of the sound and the amplitude of the sound relative to the threshold level for that frequency.

The threshold of hearing adapts to the sounds that are heard, so that the threshold increases greatly, for example, when loud noises accompany soft music. The louder sound masks the softer, and the term masking is used of this effect. Note that this is in direct contradiction of the “cocktail-party effect,” which postulates the ability of the ear to focus on a wanted sound in the presence of a louder unwanted sound.

The masking effect is particularly important in orchestral music recording. When a full orchestra plays fortissimo then the instruments that contribute least to the sound are, according to many sources, not heard. A CD recording will contain all of this information, even if a large part of it is redundant because it cannot be perceived. By recording only what can be perceived, the amount of music that can be recorded on a medium such as a CD is increased greatly, which can be done without any perceptible loss of audio quality.

Musicians will feel uneasy about this argument because they and many others feel that every instrument makes a contribution. Can you imagine what an orchestra would sound like if the softer instruments were not played in any fortissimo passage? Would it still be fortissimo? Would we end up with a brass band, without strings or woodwinds? My own view is that the masking theory is not applicable to live music, but it may well apply to sound that we hear through the restricted channels of loudspeakers. In addition, how will a compressed recording sound when compared to a version using HCDC technology?

MPEG coding starts with circuitry described as a perceptual subband audio encoder. The action of this section is to analyze continually the input audio signal and, from this information, prepare data (the masking curve) that define the threshold level below which nothing will be heard. The input is then divided off in frequency bands, called subbands. Each subband is quantized separately, controlling the quantization so that the quantization noise will be below the masking curve level for that subband. Data on the quantization used for a subband are held along with the coded audio for that subband so that the decoder can reverse the process. Figure 21.2 shows the block diagram for the encoding process.

Figure 21.2. Block diagram for MPEG encoding.

21.4.1. Layers

MPEG1, as applied to audio signals, can be used in three modes, called layers I, II, and III. An ascending layer number means more compression and more complex encoding. Layer I is used in home recording systems and for solid-state audio (sound that has been recorded on chip memory, used for automated voices, etc.).

Layer II offers more compression than layer I and is used for digital audio broadcasting, television, telecommunications, and multimedia work. The bit rates that can be used range from 32 to 192 Kbit/s for mono and from 64 to 384 Kbit/s for stereo. The highest quality, approaching CD levels, is obtained using about 192–256 Kbit/s per stereo pair of channels. The precise figure depends on how complex an encoder is used. In general, the encoder is from two to four times more complex than the level I encoder, but the decoder need be only about 25% more complex. MPEG level II is used in applications such as CD-i full-motion video, video CD, solid state audio, disc storage and editing, DAB, DVD, cable and satellite radio, cable and satellite TV, ISDN links, and film sound tracks.

Layer III offers even more compression and is used for the most demanding applications for narrow band telecommunications and other specialized professional audio areas of audio work. It has found much more use as a compression system for MP3 files (see 21.5 MP3).

MPEG-1 is intended to be flexible in use, so that a wide range of bit rates from 32 to 320 Kbit/s can be used, with a low sampling frequency (LSF) of 8 Kbit/s added later. Layer III allows the use of a variable bit rate, with the figure in the header taken as the average. Decoders for layers I and II need not support this feature, but most do.

Table 21.1 shows the relative complexity of encoding and decoding for the three levels of MPEG-1. The encoding process is always more complex, but the relative complexity of the decoder is less.

Table 21.1. Comparing Complexity of Circuitry for MPEG-1 Levels

Complexity
Layer	Encoder	Decoder
I	1.5 to 3	1.0
II	2 to 4	1.25
III	7.5 or more	2.5

MPEG-1 coding can be applied to mono or stereo signals, and the stereo system makes use of joint stereo coding, a system that achieves further compression by seeking out redundancy between the two channels of a stereo signal. The system supports four modes:

mono stereo	joint stereo
(intensity stereo or mid/side stereo)	dual channel (two independent channels, e.g., for two languages)

When the digital signal has been encoded, it is divided into blocks of 384 samples (layer I) or 1152 samples (layers II and III) to form the unit MPEG-1 frame. A complete MPEG-1 audio stream consists of a set of consecutive frames, with each frame consisting of a header and encoded sound data. The header of a frame contains general information such as the MPEG layer, the sampling frequency, the number of channels, whether the frame is CRC protected, whether the sound is an original, and so on. Each audio frame uses a separate header so as to simplify synchronization and bit stream editing, even if much of the information is repeated and hence redundant. A layer III frame can achieve further compression by distributing its encoded sound data over several other consecutive frames if those frames do not require all of their bits.

One important point about all digital audio systems is that the analogue concept of S/N ratio is no longer relevant, and so far no replacement has been found. If we try to measure S/N in any of the ways that work perfectly well for analogue signals, the results are widely variable and have no correspondence with the signal as heard by the listener.

• Note that the MUSICAM algorithm is no longer used, it was developed into MPEG-1 Audio Layers I and II. The name MUSICAM is a trademark used by several companies.
• MPEG-1 is one of several (seven at the last count) MPEG standards, and we seem to be in danger of being buried under the weight of standards at a time when development is so rapid that each standard becomes out of date almost as soon as it has been adopted. Think, for example, how soon NICAM has become upstaged by digital TV sound.

21.5. MP3

MP3 is a high-compression coding and decoding system that is now used for transmitting audio signals over Internet links and for storing audio signals in compact computer file form. MP3 allows the construction of small players that store, typically, 40 min of music, but contain no moving parts. Because MP3 is a lossy form of compression, the MP3 deck for hi-fi systems has not emerged so far, but we should remember that the compact cassette was also considered unfit for hi-fi uses in its initial days. The Minidisk uses similar compression methods.

The name MP3 began as an extension to a filename, devised to distinguish sound files created using MPEG-1 Layer III encoding and decoding software. The PC type of computer makes use of these extension letters, up to three of them, placed following a dot and used to distinguish file types. For example, thoughts.txt would be a file called thoughts, consisting purely of text, and thoughts.doc would be a document called thoughts, which could contain illustrations and formatted text, even sounds. A file called thoughts.jpg would be a compressed image file, and thoughts.bmp would be an uncompressed image file. There are many such extensions, each used to identify a specific type of file.

The same MP3 extension is used for sound files that have used MPEG-2 Layer III with a reduced sampling rate, but there is no connection between MP3 and MPEG-3. MP3 files use a compression ratio of around 12:1, so that MP3 files stored on a recordable CD will provide about 12 h of sound. See later for a description of DAM-CD.

The main use of MP3, however, has been the portable MP3 player, which allows MP3 files to be recorded from downloads over the Internet. This has made MP3 very much of an audio system for the computer buff, but like all matters pertaining to computing, this use is likely to spread. MP3 is unlikely to appeal to those who seek perfection in orchestral music (let’s face it, what system does?) but for many other applications it offers a sound quality that is at least as good as anything that can be transmitted by FM radio or obtained from a high-quality cassette.

• The advantages are many. You can load the memory up with music that you like, deleting anything you don’t want to hear again. You can play tracks in any order, select tracks at random, and store other music on your PC until you want it on your MP3 player.

One other attraction is rather an illusion, that music is free. Many Internet sites offer MP3 files at no direct cost, but you have to pay for the large amount of telephone time you need for downloading them. Unless you want only fairly small-scale works you will need a fast Internet connection, such as you get with cable TV firms. The alternative is to spend a lot of your income paying for BT phone calls, although alternatives are appearing almost daily. If you really want to download a lot of music it makes sense to take out a fast line or use one of the offers of a fixed charge for unlimited Internet use. Either way, your music is not exactly free.

In addition, “free” music is often made by unknown artists in strange places. Sometimes you will find an excellent recording made by a Russian orchestra that is unable to raise the money to make CDs or to go on tour. Other recordings may have quite awful quality, and there is always the suspicion about some of the worst recordings that some tracks may even be acquired illegally, using miniature recorders taken to live concerts. Some may even be copied from existing CDs. However, the MP3 system is an excellent way for any person or group to make and record their own music and distribute it worldwide without the costs involved in making a CD.

• There is nothing illegal about possessing MP3 files, no matter how they were obtained originally, on your computer. If you make copies and distribute them, that’s another matter, and the usual laws of copyright apply. It is certainly illegal to convert CD tracks and distribute the music in MP3 format without the permission of the copyright holder.

21.6. Transcribing a Recording by Computer

The standard hi-fi methods of copying music for your own use include cassette recording, DAT, and now CD-R or CD-RW. With the help of a computer you can go considerably further by editing the music (cutting out scratches, for example, in old vinyl-disc recordings) or by recording to MP3. The following paragraphs summarize the methods used for computer manipulation of sound for any digital form of recording, mainly CD-R and MP3. The computer must contain a sound card with a A-D converter that is up to CD quality standards, and if you want to record your own CDs you will also need a CD writing drive with appropriate software such as Adaptec Easy CD Creator. For MP3 files you will need software such as Winamp.

This is not intended to be an exhaustive guide to using a computer for manipulating audio files, as space does not permit a thorough treatment of such a large topic. If you are an experienced user of a PC computer, this is a guide to its use for audio work, and if you do not use a computer, it is a guide to what you are missing.

The first step to the creation of either an MP3 file or a CD-R disc is to extract music tracks and digitize them in an uncompressed format using a type of file distinguished by the extension letters WAV, hence called a WAV file. Some software will carry out this action automatically, reading in the audio tracks and converting to MP3 or to CD-R without leaving a WAV file behind on the computer’s hard disc. As applied to a CD as source, this action is often termed CD ripping. Whether you are aware of it or not, WAV files are always created as an intermediary, and it’s an advantage if you can store them in the computer, check them, and possibly edit them before you save them in MP3 or CD-R format and delete the WAV versions.

You are not obliged to use a CD as a source, though, and many users of MP3 or CD-R are more concerned with taking tracks from old 78s, from LPs, or from cassettes, even from radio or private recordings. Remember, however, that no matter what source you use, working at CD quality will require disc space on your computer of around 700 Mbytes for a full CD.

If you are using a CD as your source, you must use the digital output from the CD drive or deck. It is certainly possible to connect the audio output of a CD deck to the line input of the sound card on your computer and to create WAV files in this way, but this sacrifices quality. Most computers fitted with a CD writer will also have a fast CD reader, allowing you to read digital data at 36 times (or more) the normal recording speed. This also ensures that the digital output of the CD is used.

• The normal setting on most CD copying software gives you a 2-s gap between tracks when you are working in “normal mode,” which is track-at-once. If you specify disc-at-once, you will not get any added gaps between the tracks, so if you want extra time between the tracks you have to edit the WAV files so as to include silent intervals. If your list of tracks shows separate files, the recording will always place track markers so that you can move to any track in the usual way.

You can also create WAV files using any other audio source, such as 78s, LPs, cassettes, and DAT tapes. The conversion quality will be lower, because these sources all provide analogue signals of varying quality and signal level. You will need to do a few experiments with connections and signal levels, and this is why it is such an advantage to make a separate conversion to WAV, because you can play back a WAV file that is stored in the computer without the need to waste space on CD-R with an unsatisfactory recording or to make a useless MP3 file. You must, incidentally, use a modern 16-bit sound card—do not try to work with analogue to digital conversions using the older 8-bit type of card. Any computer that is fast enough to cope with audio work will almost certainly be fitted with a 16-bit card. Remember, however, that the quality of A-D conversion may not be as good as you would like.

The usual advice is to connect the audio output from the source device to the line- in connector, usually a 3.5-mm stereo jack socket, on the sound card of the computer. Depending on the sound card that you are using, you may find that the line- in is much too insensitive and that you hear virtually nothing when you replay the WAV file. The only option, unless you have a spare preamp to connect between the signal source and the sound card, is to use the MIC input. This, by contrast, may be too sensitive, leading to overloading.

The important thing is to try this out with a short piece of music before you start making any recordings to CD-R or MP3. The typical software that you will be using for creating the WAV file is Creative Wave Studio, which permits you to make a short recording to test sound levels. Using the software control panel illustrated in Figure 21.3, you can adjust the level of the signal on its way to the WAV file, but this will not help if the input stage of the sound card is overloading.

Figure 21.3. A typical software mixer panel as seen on the computer screen.

You can then play this back, either through the loudspeakers of the computer or by way of a connection to a hi-fi system, using the output jack of the sound card. The same software, incidentally, allows you to edit a WAV file to remove gaps and, after some practice, unwanted sounds, such as scratches and thumps.

You may need to make some setting-up steps, and although some software will do this almost automatically you should check the following:

• Record options must be set to stereo, 8 or 16 bits, 44.1 kHz sampling rate. Use 16-bit data for CD or other high-quality sources.
• Type in the name that you want to use for the WAV file and a folder (directory) on the computer’s hard disc where you want to store the file. The usual pattern is to select a name that will describe the music, such as Beethoven 5 Symphony, and store it where you can accommodate a large file of up to 700 Mbytes.
• Check that you have set the recording levels correctly.
• Click the Record icon on the screen and start the source playing. The screen display will probably show the progress of the recording.

You can make your recording one track at a time, making a separate WAV file from each track, or you can make a single file of the whole input. A single file uses less space (because it eliminates the “overhead” involved in making a separate file for each track), but it makes finding individual tracks (if you need to) more difficult. Software products such as LP Ripper or Adaptek Spin Doctor will work on the WAV file and separate out the tracks for you, whereas others will edit the WAV files manually.

The topic of editing a WAV file is too specialized for this book, but the principles are not difficult, and some practice with a short file is more useful than any amount of text instruction.

21.7. WAV Onward

The WAV file is, however, an intermediary. It takes up a large amount of space on your hard disc because it is totally uncompressed, and its main purposes are to allow you to edit the sound and to provide a source for conversion to MP3 or CD-R. Conversion to CD-R is a critical process because the recording will be ruined if digital data are not available when the CD writer software needs it. By using the WAV intermediate you are assured of this, because this is a file that is already in digital form, and there is no need to wait for audio signals to be converted at the risk of not keeping up with the demand from the CD writer.

To record the WAV files in CD form, place a blank CD-R disc into the recorder and use a good piece of software such as Adaptek’s Easy CD Creator. This allows you to choose to make a Data or a Music CD, to select WAV files to record, and put them into the order you want. Once you have files ready, the software will test the files and then make the recording. The disc will be ejected once the recording has been made. You can use another option of the software to print front and back covers for the CD jewel case. A CD made in this way will play in any reasonably modern CD player. On test, a CD I prepared in this way worked even on a very old Philips CD deck (the first model sold in the United Kingdom) with no problems.

If you are preparing MP3 files you need no hardware, only software. All MP3 software is not equal, and some are concerned much more with tricks than with quality or speed of conversion. The software will usually allow a choice of bit rate, and the usual rates are 128 Kbits/s for files sent over the Internet and 198 Kbits/s for files to be stored on CD-R. At 128 Kbits/s, a 4-min piece of sound will need 3.8 Mbytes of storage space, as distinct from closer to 40 Mbytes for an uncompressed CD-quality file.

Recommended software includes MusicMatch JukeBox 4.1, AudioSoft Virtuosa Gold 3.1, and XingMP3.

21.8. DAM CD

DAM is an acronym for digital automatic music, and a DAM CD is one that can contain music both in MP3 format and in normal uncompressed CD format. The MP3 tracks can be copied into any MP3 player, and the normal CD tracks can be played using any normal CD player. It is equally possible to make a DAM CD that contains only MP3 tracks, so packing about 10 times more music on to the CD than would be possible using uncompressed CD methods. If you use the computer extensively as a music player, you can transfer your favorite music into this format for easy access and compact storage.

You can also buy DAM CDs over the Internet. They often feature unknown artists and are priced accordingly, although you should not expect a large selection of classical music to be available. The CD is usually offered on the Web page for the artist, and costs are kept low by using CD-R so that the music you want is transcribed to a CD when you place your order.

• Some older CD decks cannot cope with DAM CDs that inevitably use multisession methods.

21.9. DVD and Audio

The CD format was standardized at a time when digital recording of sound on disc was still an uncharted realm, full of possibilities and surprises, and CD technology strained at the limits of what was possible, particularly A-D and D-A conversion methods. The use of lasers to write the master discs, although not new because of the Philips “silver discs” used for video recordings, was unfamiliar to many recording companies, and the extent of the packing of bits on the CD stretched the pressing capabilities of all but a few users. Now, at least two decades on, we can see that the potential of the little CD is much greater than we could have hoped for.

DVD, originally the acronym of digital video disc, is now taken to mean digital versatile disc and refers to a more recent development of CD technology. This was originally directed to recording full-length films on CD, hence the “video” in the original title, but the idea has been extended to a universal type of disc that can be used for films, audio, or computer data interchangeably. The main difference, at present, is that there are very few DVD writing drives available, and these few are expensive by computing (although not by hi-fi) standards.

• An important feature of a modern DVD computer or TV drive unit is that it will accept conventional CDs as well as DVD discs.

The DVD holds much more data, can transfer it faster, but is as easy to reproduce by stamping processes as the older CDs (which, alas, does not mean that it will be sold at reasonable prices in the United Kingdom, even if a DVD costs so much less to produce than a videotape). Eventually, DVD will be the one uniform recording format, replacing cassettes, DAT, videotape, and CD-ROM. A DVD drive is already virtually a standard item on computers, and the manufacturers claim that in a time of 3 years it has become the most successful electronics product of all time for home use (Figure 21.4).

Figure 21.4. The rear of an APEX AD 600A DVD player that also plays CDs and MP3 files, priced in the United States at about $150.

Computers are the main end use of DVD at present, but DVD drives to replace videocassette players are already widely available. The spread of DVD as a replacement for VCR, however, is not likely to spread widely until the recording version reaches an acceptable price level. Surveys have shown repeatedly that the most common use for VCRs in the United Kingdom is to record TV programs either when the viewer is not at home or when two interesting programs are being broadcast at the same time. Use of DVD simply to play prerecorded discs is very restrictive—I cannot think of more than a handful of films I would ever want to see again, and some of my own videotapes have not been played since the day I recorded them. This is mainly a United Kingdom attitude, and the laser disc that was rejected in the United Kingdom has survived up until now in other countries.

• With the primary markets of computers and film viewing now being supplied, we are waiting for a standardized DVD format for audio that reportedly will allow up to 17 h of CD quality to be stored on a single disc.

DVD offers so much more storage space than CD that the options it allows are more than most users can cope with at first. A single-layer disc can store just over 2 h of digital video signals at a higher quality than is possible using VCR (which relies on considerable bandwidth reduction). More than one layer of CD recording can be placed on a disc, however, because the layers are transparent, and by altering the focus of the reading laser, it is not technically difficult to read either of two superimposed layers that are only a fraction of a millimeter apart.

By making two-layer DVDs the recording time can be doubled, and by adding double-sided recording it can be doubled again to 8 h of video. The discs can contain up to eight audio tracks, each using up to eight channels, so that films can contain soundtracks in more than one language and cater for surround sound systems.

The DVD can also end the concept of a film as a single story because, unlike tape, it can switch from one set of tracks to another very quickly, allowing films to be recorded with several options endings, for example. Different camera angles can also be selected by the viewer from the set recorded on the disc, and displays of text, in more than one language, can be used for audio and video tracks. Like CD and so unlike VCR, winding and rewinding are obsolete concepts, and a DVD can be searched at a very high speed that seems instantaneous compared to VCR. The disc is also smaller than a videocassette, does not wear out from being played many times, and resists damage from magnets or heat.

• DVD for video uses MPEG-2 coding and decoding, but there is nothing to prevent cut-price producers from coding with MPEG-1, producing the same video quality as a VCR. Even MPEG-2, however, is a lossy compression method, which sometimes shows in video quality as shimmering, fuzzy detail, and other effects.
• In contrast, DVD audio quality is excellent. DVD audio can optionally use CD methods (PCM) with higher sampling rates for even better quality than CD. Other options, used mainly in connections with films, are Dolby Digital or DTS-compressed audio.

21.9.1. Regionalization

Unlike audio CD, DVD is more regionalized than we would wish. Taking a cynical view, this is done to prevent European users from flying over to the United States to stock up with DVDs at bargain prices. Film studios have taken the same attitude to DVD as the record companies did to DAT—if you can’t ban it, cripple it. The official reasons are that regionalization prevents premature release of a file in another country and protects the distribution rights of suppliers in different countries. Regionalization does not apply to DVDs that consist purely of audio signals.

Apart from regional codes, DVDs must be designed to work with the type of color TV coding that different countries use, so that DVDs have to be manufactured in NTSC, PAL, and SECAM versions.

The DVD standard includes regional codes, and each DVD drive or deck is allocated a code for the region in which it is marketed. A disc bought in one region will not play on a deck/drive bought in another region, because the codes will not match. Several DVD users in the United Kingdom have countered this by buying their DVD equipment in the United States and then also buying the discs in the United States.

The established regions are:

1. United States, Canada, U.S. territories
2. Japan, Europe, South Africa, Middle East (including Egypt)
3. Southeast Asia, East Asia (including Hong Kong)
4. Australia, New Zealand, Pacific Islands, Central America, Mexico, South America, Caribbean
5. Eastern Europe (Former Soviet Union), Indian Subcontinent, Africa (also North Korea, Mongolia)
6. China
7. Reserved
8. Special international venues, such as airliners and cruise ships

The manufacturers of discs are not obliged to use these codes, and if they do not do so the discs can be used on any drive/deck anywhere in the world. Some types of drives/decks can be modified so that they will play DVDs irrespective of regional coding.

• DVD-ROM discs that are used for computer software are not subject to region codes, nor are audio DVDs.

21.9.2. Copy Protection

DVDs can use four different methods of copy protection systems. The Macrovision system includes signals that will cause a VCR to record incorrectly by feeding incorrect information to the synchronization and automatic level control circuits. CGMS is designed to prevent serial copying (making copies of copies). CSS (Content Scrambling System) is a form of data coding supported by film studios, but the coding algorithm has been cracked and posted in the Internet (along with methods for defeating other protection systems), casting doubt on the future of this method. Finally, the DCPS (Digital Copy Protection System) is designed to prevent perfect digital copying between devices that incorporate this coding system.

21.9.3. DVD-Audio

The first DVD drives started to appear around 1996, but at that time there was no agreed format for DVD-Audio, despite the obvious advantages of DVD for audio recording. Considerable effort has gone into defining standards, but the final specification was approved in February 1999. Any delays were caused by the introduction of copy-protection codes as demanded by the music industry.

The situation now is that it is possible to design universal DVD players that will deal with both DVD-Video and DVD-Audio, but decks intended for DVD-Audio only will not play DVD-Video. As a further complication, because DVD-Audio is a rather different format, some DVD-Audio discs will not be fully usable in any DVD-Video player other than a universal type, which at the moment is not in production or even planned. With some cooperation from manufacturers it would be possible to turn out DVD-Audio discs that would operate on all DVD decks or drives. As usual, it is unwise to be a pioneer consumer, just as it was in the Beta/VHS days.

The protection system that has been adopted uses what the manufacturers call a digital watermark. This adds signals that appear as low-level noise, and the recording companies claim that this is completely inaudible. If enough audiophiles can hear the difference, then it is a distinct possibility that two separate audio markets could develop, one using the older CD format for music acceptable to enthusiasts, with DVD used for all other recordings. However, we may feel that the golden-eared brigade can always detect the inaudible, even on discs that have not had the coding added, but most users will not be affected.

• Sony and Philips, who developed the CD standards, have joined forces again to make their Super Audio CD format that competes directly with DVD-Audio. This takes us all back to the VCR battles of VHS and Beta, but manufacturers are likely to respond by making playing decks that will allow the use of either type of disc. At the moment, neither players nor discs are in plentiful supply.

Although DVD drives will read CDs, they will not in general read CD-R discs, and since recordable DVD is still rather distant, this might be a stumbling block to anyone who is contemplating transferring a treasured collection of tracks to CD-R. However, most DVD players can read CD-RW discs. This difference arises because DVDs use a laser whose light color is not the same as is used for CD players, and this light does not match that used for CD-R, although it is better adapted to CD-RW.

At present, I would not urge anyone to rush out and buy DVD-Audio, even if equipment becomes available on the United Kingdom market. The list of incompatibilities already suffered by DVD-Video (films that will not play on specific players) is very long, and we simply can’t guess how many problems of the same type we might see with DVD-Audio. For the long term, however, the medium must be the future of audio and video distribution. In the United Kingdom, much depends on making recordable DVD at a price that is not too much out of line with VCR, which is a tall order even when all TV is digital. As to DVD-Audio, its day will come when all record companies start to distribute on DVD rather than on CD.