Side-Chain Processing

Within the VST 3 specification, the ability to apply side-chain signals to plug-ins directly has been added. With VST 2 plug-ins, convoluted workarounds were employed to get similar results with limited success. Now, using side-chain inputs is as simple as assigning an output for a send or a channel directly to a side-chain input.

VST 3 plug-ins that are capable of having a side-chain input now have a new button in the GUI. Enabling this button adds the side-chain input as another available destination in the output routings for channels and sends. With the compressor plug-in inserted into an audio channel and the side-chain activated, a side-chain input is now available as a destination for other channels and sends. (See Figure 14.13.)

Figure 14.13 Side-chain input as routing destination.

Side-Chain Inputs Side-chain signals are primarily used by dynamics processors: compressors, gates, expanders, etc. They allow signals to trigger the action of the plug-in without the same signal running through the plug-in and being processed.

For example, let’s say you insert a compressor on a bass track and activate its side-chain input. You can then route a send from the kick drum channel to the side-chain input of that compressor. The result is that the bass will be compressed by the kick drum signal. In other words, when the kick attacks, it will cause the compressor to act upon the bass signal, pumping it along with the kick drum. The result can be a feeling of the bass and kick drum locking in more, tightening up.

Bob Clearmountain Console De-Essing Technique

A more sophisticated application of the side-chain signal can be found in veteran mixer Bob Clearmountain’s de-essing technique that he performs on an SSL console. The basic idea is that he uses a second channel strip to both equalize and set the level of the side-chain input on a lead vocal channel. He then automates the side-chain channel to control the amount of de-essing throughout the song.

Here’s how to set up this technique in Nuendo:

1. Duplicate the lead vocal track and name it De-Ess Signal or something similar. (See Figure 14.14.)

Figure 14.14 Copy and rename the vocal track.

2. On the lead vocal track, insert a VST 3-compatible compressor plug-in and activate the side-chain input.

3. Route the De-Ess Signal channel to the side-chain input of the compressor. This has, in essence, created the same result as if the compressor plug-in did not have its side-chain activated. The normal lead vocal signal will trigger the compressor as usual. (See Figure 14.15.)

Figure 14.15 Mixer with lead vocal and De-Ess Signal tracks.

4. Equalize the De-Ess Signal to emphasize the offending ess frequencies. These typically lie in the 3-11 kHz range but are completely dependent on the individual voice. You may Listen-enable this channel to closely EQ the signal to isolate just the strongest ess sounds. (See Figure 14.16.)

Figure 14.16 EQ of De-Ess Signal to isolate ess sounds.

5. Adjust the level of the De-Ess track so that it triggers the compressor only on the strong ess sounds. It may be necessary to adjust the threshold and ratio of the compressor to achieve the desired result. Try to set it up so that normal ess sounds get compressed with the De-Ess Sig fader down a bit, -6 dB or so. This will give you more room to adjust in different sections of the song.

6. Get a feel for how adjusting the level of the De-Ess track affects the reduction of esses in the vocal. Run the track and play with the level of this channel to see how it affects different sections of the music.

7. When you are ready, use automation to record changes in the De-Ess level to achieve just the right amount of de-essing for each phrase of the vocal. In softer sections you might lower the level to let more detail through, while during loud passages, more de-essing could be needed. Simply turn up the fader to get as much de-essing as you need. (See Figure 14.17.)

Figure 14.17 Automation curve of de-essing track.

8. You can go back and edit the automation data to get more precise timing of the de-essing process. Also, the EQ can be tweaked to refine how the compressor reacts to the De-Ess Signal.

Note Automation will be covered in Chapter 15, “Automation.”

This method allows an amazing amount of control while also making a painful and tedious process quick and intuitive using fader automation. This is another example of how parallel paths can create complex routing schemes to help streamline the mixing process. With side-chain signals, more options are on the table for signals to interact in creative and surprising ways.