Side FX

From de-essing to complex drum processing, side-chain access in Studio One opens up many new possibilities.

Many software dynamics plug-ins, not to mention a great many hardware processors, allow manipulation of the side-chain signal. This is the portion of the control signal path that feeds the level detector, which controls the gain element, triggering compression, gating or what have you. Probably the most familiar example of side-chain processing is de-essing, in which an EQ is inserted in the side-chain of a compressor to emphasise energy in the sibilance frequency range, making the compressor more reactive to sibilant words. However, there are many other applications for side-chaining, including cross-gating (where a kick drum can gate the notes on a bass guitar, for instance) and ducking. This month, I'm going to show you a few side-chain applications using Studio One's bundled Compressor, Gate and Expander plug-ins.

Reduce LF Pumping

Where the signal fed to a compressor contains a lot of low-frequency content, this can produce exaggerated gain changes in the wide-band audio, a sound described as 'pumping'. This can be particularly annoying on synthesized sounds with a lot of low-frequency content. One simple remedy is to flip de-essing on its head: instead of making the compressor more sensitive to high-frequency content, we insert an EQ with a low-frequency roll-off or dip to make the compressor less sensitive to low frequencies, thus reducing pumping. Figure 1b shows how this works. The easiest way to set this up is to use the side-chain filtering built into plug-ins such as Studio One's Compressor; however, it is also possible to route a signal bound for a side-chain through a bus channel with an EQ plug-in inserted on it. Figure 1: a) Basic de-essing setup, b) pumping caused by low-frequency energy can be reduced with a high-pass EQ in the side-chain, c) the Compressor plug-in's onboard side-chain EQ section.

Ducking School

'Ducking' is the name given to a technique where a compressor across one signal is triggered from another, thus diminishing its level only when the second signal is playing. Radio and TV ads often use pretty brutal ducking to get music out of the way of the announcer's voice, for instance. Ducking also has a role in music mixing, albeit usually with much smaller amounts of gain reduction. For example, having the lead vocal duck a reverb or delay tail just 1 or 2 dB can impart much more clarity to the vocal without sacrificing the effect of the reverb or delay. Figure 2 shows the Compressor plug-in set up to duck a heavy guitar track a tad when the lead vocalist is singing.Figure 2: a) Basic ducking for music: a lead vocal channel feeds the side-chain of a compressor on a guitar submix, b) a typical Compressor setting for music ducking. Note that the Expander plug-in can also be used for ducking when the Duck button is selected.

For somewhat more sophisticated ducking application, let's consider a band where each musician takes a solo in turn, and at the mix, we want each soloist to duck some or all of the other instruments. Accomplishing this requires two things: sending each soloist's signal to the side-chain at the appropriate time, and keeping the soloist from being one of the ducked tracks. Both goals can be attained if we use a bus channel to feed the side-chain, and have submixes of the instruments we want to duck. Let's say we want to bring out a guitar solo that is being supported by keyboards, a rhythm guitar, background vocalists, bass and drums, and which is followed by a keyboard solo.

• Make a bus channel through which we will route the soloists. Name it 'Solos' and route it to the main output.
• Make another bus channel, name it something like 'Instrument submix' and route the keyboards, lead guitar and rhythm guitar through it.
• Do the same again to create a submix for the background vocals.
• Insert the Compressor plug-in on each of the two submix channels. Now our gain elements are set up. (We probably don't want to mess with the groove, so we are not going to worry about ducking bass and drums.)
• Go to the Solos channel and create a send. As its destination, move the cursor down the destination menu to the word 'Sidechains', click it, and select the Compressor on the 'Instrument submix' channel.
• Repeat the previous step to create another send, but this time choose the vocal submix as the destination. Now, our Solos channel will feed both compressor side-chains and trigger ducking.
• Finally, go to the lead guitar channel and create a send to the Solos channel. Click the button to make the send pre-fader, and click the send on/off button to disable the send. Repeat this step for the keyboards channel.
• When the lead guitar solo comes in, automate the lead guitar channel to mute, and the send on that channel to unmute. Since the send is pre-fader, the signal goes through the send to the Solos channel, while it is removed from its normal routing through the rhythm submix channel. The Solos channel feeds the main output directly, so the solo is heard, and the sends from the Solos channel cause ducking to happen.
• Adjust the Solos channel fader and send levels, and the Compressor settings to produce a good mix of the solo and a dB or two of ducking of the submixes.
• Repeat the previous step for the keyboard solo. Adjust send levels from the lead guitar and keyboard channels to get appropriate levels through the Solos channel.Figure 3: Signal flow for solo-triggered ducking. When the lead guitar solo starts, the lead guitar channel is automated to mute, while its send to the Solos bus is automated to unmute. Thus, the lead guitar solo triggers ducking, but is itself removed from the ducked submix. These settings are reversed at the end of the solo.>

At the mix, you'll sometimes want to use effects on solo sections that aren't used on the same instrument in the rest of the song, and there are several ways effects can be handled here. One is that they can be inserted on the solo instrument's channel and bypassed, then automated to kick out of bypass just for the solo. That way, the sound being sent to the Solos channel is always the complete sound for the instrument. Alternatively, effects can be inserted on the Solos channel and automated in and out. Yet another method is to use sends from the solo instrument channels to bus channels on which the effects are inserted, with the bus channel outputs routed to the Solos channel or directly to Main Out.

Cross-gating

I've already mentioned the basic 'kick triggers gate on bass' application for cross-gating, so now I'm going to give you something a little more interesting to chew on: an intriguing mashup of cross-gating and drum replacement intended to enhance an existing track. It's kind of like velocity layering in samplers, adapted for recorded tracks. First, pick a recorded track to enhance. For the purposes of learning this trick, try something transient and dynamic, like a snare drum.Figure 4: Signal flow for volume-triggered enhancement.The submix at the end is not required, but makes things easy.

• Make a new bus channel in the mixer and create a send to it from the snare channel in the mixer. Set the send on the snare to pre-fader, so that the signal is not affected if you adjust the snare level. Name the bus channel something like 'Snare enhance trigger'.
• Insert the Gate plug-in on the bus channel and click the Active button in the Trigger section. Every time the gate is opened by the signal, a note will be generated with the note and velocity values set here.
• Play the track and adjust the Threshold Open knob until the gate is triggering. You can tell the gate is opening by watching the gain-reduction meter, and you'll see a note being triggered by the flashing of a note icon in the Trigger section. Set the threshold so that triggers are being generated with some regularity — fine-tuning comes later!
• Since the channel inserts precede the channel fader and mute button in the signal path, you can mute the bus channel (or lower the fader) to remove its audio from the mix without affecting the triggering.
• Set up an instrument track with a virtual instrument playing a sound you want to use to enhance the snare. For my example (go to /sos/jan14/articles/studioonemedia.htm) I instantiated PreSonus's SampleOne sampler, put a synthesized snare sample into it, and then added some flanging for tonal variation on the SampleOne channel in the mixer.
• In the the SampleOne track, choose Gate as the Instrument input and enable input monitoring for the track.
• Play the song. You should now hear SampleOne being triggered by the snare track. Adjust the gate threshold parameters until only hits above a certain volume result in triggers. Now, the loudest hits get enhanced by the sample, but the rest do not. Record-enable the instrument track and press Record, and it will capture the triggers. (If you do not do this, you will always need to have input monitoring enabled to hear the effect.)
• There are additional benefits from this arrangement. For example, you can make the bus channel do double-duty for parallel compression by leaving it unmuted and inserting a compressor after the gate. Note that the compressed signal doesn't even have to be gated if you don't want it to be, even though it is passing through a gate. Simply set the Range control on the Gate plug-in to its maximum (0dB). Note triggers are generated only by the signal exceeding the gate threshold; the range of gain reduction is irrelevant to this.

Comparisons

Figure 5: The Pro EQ and Spectrum Meter plug-ins can provide side-by-side spectral analyses for comparing two signals. One signal is the channel on which the EQ is instantiated, the other enters through the side-chain input.

I will leave you this month with one last interesting side-chain application Studio One offers. If you send a signal from a channel to the side-chain of a Pro EQ or Spectrum Meter plug-in instantiated on another channel, the plug-in will display spectral analyses of both signals, one above the other, making comparisons a snap. (Pro EQ must have its Spectrum mode set to FFT Curve to see both analyses.)