5
Audio Editing

Fortunately, time has a wonderfully leavening effect on our memories. I can still vividly remember my early attempts to record the many and varied sounds at a family theme park in Vermont on a bulky Telefunken tape recorder, while simultaneously filming the different exhibits on my trusty Bauer cinecamera. After waiting impatiently for the film to be developed, the 3-minute reel finally arrived in the post and the projector and tape recorder were set up, side by side, the projection screen was placed in position and all the appropriate switches were pressed. Suddenly the room was filled with sound and light and we were transported, albeit only for 3 minutes, back in time to relive a unique experience. No matter the fact that sound and vision were hopelessly out of sync! No matter that I tripped over the tangle of wires in the room, dragging the projector off the table and breaking the case. Forgotten also was the sheer physical effort of lugging the Telefunken kit around the theme park for a couple of hours just to record 3 minutes of sound. What mattered was that it had all come together and a precious family experience – with all its sight and sounds – had been captured for the family archives!

The memory of that first success in bringing sound and vision together (well, almost) came back to me when I bought my first camcorder. How life had changed since these pioneering days. Now I had 90 minutes of synchronised sound and vision available at the press of a button and all in a package small enough to slip into a pocket (well, OK, a small carry bag).

Driven by the growing demands of the music industry, as well as by film and television, audio technology has kept pace with the rapid shift of video processing from the analogue to the digital domain. The demise of the LP – fast becoming a curiosity to be found only at car boot sales – is being followed by that of the analogue audio cassette, as it gives way to the CD ROM and digital tape.

In the professional arena, as in the case of digital video editing, the process of digital audio editing provides the editor with incredible control and flexibility in the manipulation of audio material. Once digitised, audio tracks can be cut, copied, pasted and manipulated at will, without loss of quality and all within the comfort of the editor’s own hard drive!

Audio Sources

Audio material which can be edited on the desktop is available from a wide range of sources:

  Audio captured with video on video tape

  Material recorded on analogue and digital audio tape which can be digitised via the Line In socket on a sound digitising card

  A rapidly growing range of audio CD ROMs (Capturing sound from a CD ROM requires an internal audio cable linking the CD ROM drive output socket to the audio card’s input socket)

  Speech or music recorded directly to disk via a microphone and the audio digitising card’s Mic In socket

  Midi-compatible instruments like keyboards which can connect directly to the joystick/Midi socket on a PC sound card

  Audio clips recorded on CD ROM in midi format

  Audio clips recorded on CD ROM in wav format

  Royalty free sound clips downloaded from the Internet

Material from any or all of these sources can be imported and placed on the audio tracks of any of the host videoediting applications we have been examining, where it can be edited and synchronised with video clips placed on the video tracks.

Editing in the Host Applications

All three of our videoediting applications offer facilities for importing and editing audio clips. Most commonly this involves downloading and working with audio which has been recorded simultaneously with video on to videotape. By connecting the audio output from the videocamera to the audio input of a suitable audio digitising card and by enabling Capture Audio in the capture utility (Figure 5.1), the audio track can be digitised and saved to disk with the video signal in AVI (audio video interleaved) format. When the saved file is imported, e.g. to Media Studio, then the audio clip appears in the first of Media Studio’s audio tracks (see Figure 3.10). When imported in this way, the video and audio tracks are linked to maintain synchronisation (if one is moved horizontally along the timeline, the other moves with it), but they can be separated by selecting Split from the Clip menu. As we saw in Chapter 2, recording high quality sound (44 kHz, 16 bit, stereo) involves a data rate of 172 kB/ sec, putting extra demands on the processor during capture, so it is often better to record video and sound separately and then synchronise them within the videoediting application.

While the videocamera offers the benefit of simultaneous sound and video recording, it effectively provides only one ‘take’ to get the sound right! Fortunately the audio editors provided with host applications provide a second chance, fulfilling several purposes:

  Correcting problems (e.g. amplifying sound which is too quiet or deleting that unfortunate expletive when the subject tripped over a kerb)

  Replacing or adding material such as a voice-over or musical background

  Adding special effects, such as Reverb, to modify the sound as originally recorded

When a sound clip is loaded into Media Studio’s timeline, the volume is automatically set to 100 % – the level at which it was recorded. A straight line running through the centre of the clip represents the volume setting. Changing the volume involves clicking a point on the line (Figure 5.2) and dragging up to increase, or down to decrease the sound level. A common use for this feature is adjusting the start of a sound clip to fade in and the end to fade out. Double-clicking on a clip opens an audio controller for setting Punch In and Punch Out points and playing the clip (Figure 5.3 shows Premiere’s controller).

Media Studio provides a useful Silence Clip button insert a block of silence into an audio track in the timeline – helpful for creating audio place-holders. Speed or duration of a whole clip can also be altered by using controls from the Clip menu (Figure 5.4).

Mixing tracks is simplicity itself. Adding a musical background behind, for example, a voice-over clip simply involves placing the music track on a new audio track vertically beneath the voiceover clip and adjusting its level as described above.

Audio Filters

More creative audio effects are provided in the form of audio filters. Applying a filter simply involves selecting the audio clip and then selecting Audio filters from the Clip menu. Filters offered by our three host applications include the following:

  Amplify – raises or lowers the amplitude of the audio clip so that it plays louder or quieter

  Echo – adds a simulated echo effect to the clip

  Fade – provides control over the rate at which the amplitude changes at the beginning and end of the clip

  Flange – creates a simple delay-based effect which produces a ‘whooshing’ sound

  Graphic Equaliser – allows manipulation of the tone of a clip

  Long Echo – applies a predefined echo which decays quickly after a long delay

  Long Repeat – applies a predefined echo which decays slowly after a long delay

  Normalize – resets the highest peak in the clip to 100% and then adjusts the rest of the clip in proportion

  Pan – fades from one channel to the other when applied to a stereo clip

  Pitch – changes the pitch of the clip to make it sound deeper or more shrill

  Pop Removal – removes the highest and lowest values from a window of samples

  Quantize – reduces the number of bits for the audio clip, resulting in a lower quality sound

  Remove Noise – filters out low amplitude background noise

  Resonance – an echo effect which causes the sound to vibrate

  Reverse – swops the ends of the clip so that it plays backwards

  Stadium – applies an echo effect which simulates that heard in a stadium

Editing controls vary from filter to filter. Figure 5.5 shows an example from Premiere, which provides both presets and good controls for a wide range of effects.

Audio Editing in Studio 200

Sound effects, MIDI music and CD audio can be added to Studio 200 clips during the recording process. The sound to be added is mixed with the audio from the source deck before being recorded to the record deck. The Audio out from the source deck is first connected to the Audio in of the sound card and then the Audio out of the sound card is connected to the Audio in of the record deck. Sound can be recorded on to the finished video tape from any of three different sources – WAV or MIDI files stored on the PC hard drive or sound recorded from an audio CD. When an audio effect is encountered during recording to the output tape, Studio 200 automatically plays back the desired sound at the appropriate time.

To add, for example, background music from a music CD to a video clip, the clip is first selected by clicking on it in Studio 200’s EDL window (Figures 3.47 and 3.56) and the CD option is selected from the Add Effect window (Figure 5.6). This opens the Define CD Effect dialog box shown in Figure 5.7.After entering the Disk Name and Effect Name, a time is entered in the Clip Offset box (setting the time at which the background music will start to play, relative to the start time of the clip). Play back, Play, Stop, Previous Track and Next Track buttons are provided for selecting the track required and positioning a sound cue. Range Start and Range End controls are used to play a selected range of sound within the selected clip. The duration time appears in the Duration box alongside the selected range values.

The source deck can also be positioned exactly at the frame where the sound is to begin playing and then the start time for the music can be synchronised with this frame by clicking on the Current button. The amount of delay necessary to start the effect at the current point in the clip is automatically entered in the Offset field.

After the settings are complete, clicking OK adds the effect to the event list ready for recording.

Audio Utility Applications

So far, in this chapter, we have looked mainly at the manipulation and editing of audio material from within host applications like Premiere or Studio 200, but in many cases it is first necessary to capture audio from a live source or to retrieve stored material from disk for editing, before importing it to the host application. Before importing can take place, a sound clip also has to be in a format recognised by the application, such as WAV or AIF. Some examples of the many utility applications which are useful for such work are described below.

Multimedia Decks from Creative Labs (Figure 5.8) is a collection of players which can be used independently or concurrently to control multimedia devices such as a CD-ROM drive and a Midi device. It includes players called Creative CD, Creative WAVE and Creative MIDI. When Creative CD is used to play an audio CD, with Record activated in Sound ‘LE (Figure 3.8), then part or all of the CD sound track can be recorded and then saved in WAV format. Similarly, when Creative MIDI is used to play Midi either from a live Midi instrument attached to the sound card, or from a Midi file stored on disk, with Sound ‘LE activated, then the Midi track can be saved as a WAV file.

Sound ‘LE, or a similar recording utility, can also be used to record speech from a microphone connected to the Mic In socket of a sound card or sound from an audio tape deck connected to the card’s Line In socket.

Creative Mixer (Figure 5.9) is a simple audio mixer which can be used to combine and manipulate sound from various audio sources. With such a mixer, it is possible select and mix different audio sources during playback and recording.

Creative Wave Studio (Figure 5.10) can be used to combine the data contained in any number of previously recorded Wave files. Mixing the data from two Wave files adds the data from one file to that the other, creating a new file, using the following procedure:

  The first (source) file is opened and the portion of the data to be mixed is selected

  Clicking Copy places the selected data on the clipboard

  Next the second (target) file is opened and the location for mixing of the copied data is specified

  On the Edit menu, clicking Paste Mix opens the dialog box shown in Figure 5.11. This dialog box is used to specify the channel data to be mixed

  Under From Buffer Use, click the channels from which data is to be copied from the source file and under Mix With Wave click the channels for mixing data to the target file

  Clicking the OK button adds the data selected from the first file to the data in the second file at a position indicated by the cursor, or, if a portion of the target file is selected, with the portion selected

WaveStudio also provides a range of audio filters – invoked by selecting from the Special menu shown in Figure 5.12.

Even without access to a Midi instrument, applications are available which provide a further whole category of creative desktop sound effects. An example of such an application is Creative Labs’ AWE64 MIDI Synth (Figure 5.13) which provides a virtual keyboard for the addition and control of Midi effects. MIDI Synth uses wavetable synthesis to create musical notes using high quality, digitally recorded sound samples. Clicking on the Instrument menu lists a wide range of instruments and sound effects. The Controller value slider applies to the Midi Controllers menu which includes Volume, Pan position, Expression controller, Sustain pedal, Reverb depth and Chorus depth. Using the virtual keyboard in combination with these instrument and controllers, an astonishing range of effects can be created and recorded for inclusion in video projects.

For the user with musical talents, Recording Session from Midisoft (Figure 5.14) is a simple sequencer offering standard Midi sequencing features, as well as an editable musical notation display. Three windows are used to record, play, and edit musical compositions. The Score view displays the music in standard musical notation. As recording takes place, notes appear on the screen. When the composition is played back the notes highlighted as they play. The Midi List view (not shown) displays the music as Midi events, affording minute adjustments to the shape of each note. The Mixer view is used to control recording and playback of Midi files. This window contains transport controls, as well as a tempo control, song location display, and controls for adjusting velocity and volume. The Toolbox contains five icons, rep-resenting tools for working with the onscreen notation.

Corel bundles a simple to use audio utility called SmartSound Wizard with Premiere for creating custom audio clips. The utility, selected from the File/New menu offers a choice from several categor-ies of music or sound effects (Figure 5.15). Within each category, there are several styles which offer variations of the original sound track.

Using the Custom setting in the first window, a Wave file can be created which matches the running time of a specific video clip.

The process for creating a custom audio clip involves the following steps:

  In the first window, the button for either Music or a Sound Effect is selected

  A running time is then selected for the clip

  To create a music clip, in the next window a Category is selected from the list on offer (clicking on the Preview button plays a few seconds of the selected clip)

  A Style is then selected from the style list

  To create a sound effects clip, in the lower window a Category is selected

  A Style is then selected from the style list

  The default path and name of the audio file to be created is displayed. A new path and name can be entered before saving the file to disk

  Clicking Finish creates the audio file and automatically loads it into Corel’s Media Catalog

Specialised Audio Editing Applications

In the same way that digital video has extended the video editor’s image control down to every pixel on every video frame, the advent of digital audio brings a previously unimaginable level of precision and flexibility to the production and editing of sound. Each sample of the 44,000 which make up just 1 second of a digital audio track can, in principle, be accessed independently of the others for the purposes of editing; sound elements from different sources can be combined and manipulated to create exciting new hybrid effects and totally new and unique sounds can be synthesised and mixed with sounds from a wide range of natural sources.

Not surprisingly, as well as the simple applications we have looked at already, a growing range of sophisticated audio editing applications have been developed to provide sound editors with the means of working creatively with this new technology in the music, film and television industries. The cost of many of these applications can run into hundreds of pounds, but fortunately others are available as shareware, with only a modest registration cost. Some examples are briefly described below.

Goldwave

GoldWave is a versatile sound editor, player, recorder, and audio file converter (it can open and convert audio files of many different formats – wav, voc, au, snd, raw, mat, aif afc, iff, vox, dwd smp and sds).

GoldWave displays its wares in three windows (Figure 5.16) – the Main window the Device Controls window and the Sound windows. The Main window groups together and manages all the Sound windows which display open files. The status bars show attributes of the Sound window, including the sampling rate, length, selected region, channels, and general file format information. By clicking the mouse pointer over any status item that shows time, the unit or format for that status item can be changed. Clicking over the length item, for example, opens a menu showing length in terms of storage size, time and samples.

The Device Controls window interacts directly with the sound card, providing buttons to play and record sounds as well as controls for volume, balance and playback speed. LED meters and oscilloscopes graphically display audio data whenever a sound clip is played or recorded. The oscilloscopes can be configured to display graphs in several different formats

Goldwave offers the following range of features:

  An Expression Evaluator to generate sounds from simple dial tones to bandpass filters. It supports more than 20 common functions and operations. Expressions can be stored in groups for quick retrieval. Expressions for dial tones, waves, and effects are included

  A multiple document interface which allows many files to be opened at one time, simplifying file-to-file editing

  Intelligent editing operations, such as paste and mix – clipboard audio data is automatically converted to a compatible format before the data is used. This simplifies the editing process when working with files with different sampling rates, bit resolution or number of channels

  Large files can be edited using hard disk editing. Small files can be edited quickly using RAM-based editing

  Sounds are displayed graphically and the level of detail can be changed by zooming in or out. Samples can be edited directly with the mouse when zoomed in to a sub-sample level (the level at which individual samples are easily visible)

  Many audio effects (see the Effects menu in Figure 5.17) allow enhancement, distortion, or alteration of sounds in various ways

GoldWave supports both direct-to-disk editing and RAM editing. In direct-to-disk editing, the entire sound clip is stored in a temporary file where it can be modified. This allows editing of very large files of up to about a gigabyte in size, provided the required disk space is available. Only a small amount of RAM is required for each opened sound clip. In RAM editing, the entire sound is stored in RAM. This allows very quick editing and processing of files, but is of course limited by the RAM available.

Cool Edit

Cool Edit (Figure 5.18) claims to be a complete recording studio. Sounds can be generated from scratch with Generate Tones, Generate Noise, and Generate DTMF Signals. Audio clips can be ‘touched up’ with features like FFTFilter, Quick Filter, Amplify, Compress, Envelope, Stretch, Channel Mixer, and Noise Reduction. A menu of special effects includes Reverb, Delay, Echo, 3D Echo Chamber, Flanging, and Distortion. The pitch or tempo of a clip or part of a clip can be altered with the Stretch function. Newly created effects can be saved as Presets for later recall and Scripts and Batch Processing features can be used to automate many activities.

Cool Edit also offers powerful data analysis features. The Spectral View provides a multicolour map of the sounds in files. A Frequency Analysis (Figure 5.19) can be generated to see which frequencies predominate at a point or in a region of a waveform. A Statistics feature provides information on peak amplitude and minimum and maximum RMS power levels. The application even claims to create Brainwave files to induce states of deep sleep, theta meditation, or alpha relaxation!

Cool Edit can also be used to create two types of sound effect – Noise based or Tone based. Using the Generate functions, a clip of noise or tones is first created as a base for the effect, using either the Generate Noise function (Figure 5.20) or the Generate Tones function (Figure 5.21). Next the transformation functions are manipulated to create the desired effect. The kind of effects which can be created include:

  Waterfall, wind, and rain

  Thunder, snare drum, cymbals and jet engines

  Fantasy sounds such as time warp

  Siren, pipe organ, piano and other musical instruments

  Space ship sounds, whining and whistles

Using the Reverse function and the features in the Mix Paste dialog box (Figure 5.22) like Crossfade and Loop Paste, more complex sound effects can be built up.

Using Cool Edit, the process of mixing of sound clips, of different formats or specifications – e.g. mixing a mono 8-bit 11 KHz file with a stereo 16-bit 22 KHz file – is very simple. First, a new instance of the program is opened by selecting File/New Instance, then the clip to be mixed is opened in the new instance. Using Edit/Copy, the portion of the file to be mixed from the first instance is copied and then mixed with the clip in the second instance using the Edit/Mix Paste command, with the Overlap box checked. More new instances can be created to mix additional clips.

Cool Edit also provides a noise reduction feature (Transform/Noise Reduction) to remove background noise and general broad band noise with minimal reduction in signal quality. The amount of noise reduction depends upon the type of background noise, and the allowable loss in the quality of the retained signal. Increases in signal to noise ratios of 5 dB to 20 dB are claimed. The function can be used to remove tape hiss, microphone background noise, 50 cycle hum, or any noise which is constant throughout the duration of the waveform. The Noise Reduction function can also be used to create special effects by setting the noise level to some valid signal component in a sound clip waveform, rather than the background noise. Whatever frequencies are present in the highlighted selection are removed, modifying the original sound.

Multiquence

Multiquence is a multitrack audio processor with multimedia extensions for sequencing digital audio, CD audio, Midi, and video. Figure 5.23 shows the workspace, in which the various files to be used in a composition can be assembled and edited

To the left of the timeline is a master volume slider which controls the final mixing and playback volume level for all of the tracks. Just below the master volume slider is a meter which indicates the output volume level of all the tracks combined. If the maximum level is exceeded a red warning light appears in the small box to the right of the meter. The track volume sliders control the volume of individual digital audio tracks. A mute button is provided with each track to disable the track so that it is not mixed or played. The solo button does the opposite, selecting just one track for playback.

From the Edit menu a number of effects can be added to a selected audio track section (Figures 5.24 to 5.26). Flange adds a flange effect, Equalizer applies a parametric equalizer to the selected audio section, Pan sets the left/right balance and Speed sets the playback speed of the selected section. The Edit/Volumes command can be used to crossfade between two sections (fading out one section as the other fades in – Figure 5.27). Sound clips placed within the workspace can also be selected and edited using an audio editor, such as Goldwave, which has been specified in the application’s Options dialog box.

When placed on tracks, clips are colour coded for easy visual recognition – e.g. CD audio tracks are green and video tracks are magenta. Each track may contain a series of clips – called sections – which are played sequentially. From the Edit menu, Split divides the selected section at the vertical marker’s position. A new section can then be inserted at the split point or part of the original section can be dragged and dropped to another track. Trim Beginning removes the beginning of the selected section up to the marker’s position. Trim End removes the end of the selected section beyond the marker’s position. When a recording section is added to a track (e.g. Track 5 in Figure 5.23) digital audio can be recorded from a sound card input source such as line-in or a microphone. If the recording section is set to Record, the section will be recorded when the project is played. If Play is selected, the section will just be played when the project is played – useful to test how a recording sounds when combined with all the other tracks.

Unless any mute buttons are activated, all tracks play concurrently. This feature allows experimental mixing and playback of various file types, as well as adjustment of individual track volumes and relative positions along the timeline, before saving as a composite file. When a project is saved, the MPQ project file saves pointers to the clips in all the sections in each track. Up to 5 hours of material can be saved in a single project file. A project typically contains a combination of tracks and sections to create such things as music, audio CDs, radio programmes and multimedia presentations.

The File/Save As command mixes all the digital audio sections and tracks into a single Wave file for use in other applications. Only digital audio sections are mixed to the file. Midi, CD audio and video soundtrack sections must be converted to WAV format if they are to be included in the mix.

Summary

While video editing applications provide a useful range of video features for adding titles, transitions and optical filters, as we saw in the last chapter, their audio editing capabilities are generally quite limited. Audio utility applications – like Creative Labs Multimedia Decks described in this chapter – are often bundled with sound cards and provide the means of recording audio from a variety of sources in a format suitable for mixing with video. They also provide simple access to a growing range of prerecorded sounds – the audio equivalent of clipart – which can be imported for use in multimedia projects.

For more serious audio editing, a range of sophisticated (and expensive) specialised applications have appeared on the market, but fortunately low cost alternatives like Goldwave, Cool Edit and Multiquence featured in this chapter, although lacking some of the features of their expensive counterparts, provide impressive capabilities which will meet the needs of many users.