The Primary Source Expander (PSE) plugin operates in four modes, each designed for a different kind of scenario. This article explains the differences between these four modes and when to use each in order to make the most of the plugin and get the best results.
Mode 1 – Source INT, Ducking OFF
This is PSE’s default mode, in which the plugin is set to an internal sidechain source (INT), without ducking. In this mode, PSE will reduce gain whenever the input signal drops below the selected threshold. The gain will be reduced by the amount set by the Range control.
Problem: An electric guitar amplifier makes noise even when the guitar is not playing.
Solution: Insert PSE on the guitar channel to reduce noise whenever the guitar is not playing and the amp is idle.
Mode 2 – Source INT, Ducking ON
You can improve the internal sidechain behavior by using this mode, with ducking on. This is especially useful in situations where the environmental noise is inconsistent and thus prevents PSE from reducing gain in a smooth way.
When in INT Side Chain mode, ducking adds DC (direct current) to the sidechain detector. This effectively raises the sidechain’s noise floor and makes low-level detection smoother.
Increasing ducking gain improves PSE’s stability when lowering gain between phrases and contributes to consistent gain reduction. Adjust the ducking gain manually until you achieve sufficient gain reduction between phrases. Try to avoid too much ducking gain, since this can truncate the beginnings and endings of musical phrases. Use the Ducking On/Off toggle to quickly assess the results.
Problem: The vocal microphone picks up a lot of stage noise when it’s idle or when the performer tries to sing in front of the PA speakers.
Solution: Insert PSE on the vocal channel, adjust the Threshold and Range as you desire, then gently add ducking gain for consistency.
Mode 3 – Source EXT, Ducking OFF
When the sidechain is set to an external source (EXT), PSE still attenuates the gain of the channel on which it is inserted by the amount of gain reduction set by the Range control. However, in this mode, PSE is triggered by the external source (a different channel), such that attenuation occurs only when the external sidechain input level is below a certain threshold that you’ve set. When the external sidechain input level rises above that threshold, PSE will not attenuate. (In this mode the input meter behind the Threshold control represents the EXT sidechain input level.)
Problem: You’re mixing a choir, where all the members are singing together. Usually choirs are amplified by very sensitive condenser microphones, and we want to make sure that when the choir is not singing the idle mics will be attenuated to avoid stage noise leakage.
Solution: Use a “trigger” mic, as follows. Give the most powerful singer a lavaliere microphone. That microphone will not be amplified in the PA: instead, it will be used only as a trigger. Route the choir microphones to a group, insert PSE on this group, set it to EXT Side Chain, and then choose the "trigger" lavaliere microphone as the external sidechain input. Whenever the “trigger" singer is not singing, the choir mics will be attenuated by PSE; whenever the “trigger" singer does sing, there will be no attenuation.
Mode 4 – Source EXT, Ducking ON
This is a mixed mode. As in the first mode (Source INT, Ducking OFF) PSE attenuates gain when the input signal drops below the selected threshold. The gain is attenuated by an amount set by the Range control.
But in addition, whenever a loud stage source prevents PSE from attenuating consistently, this mode uses a sidechain input that triggers added attenuation, in order to help PSE attenuate between phrases. The amount of added attenuation depends on the amount of ducking gain you set. Higher ducking gain values will result in increased gain reduction. Avoid excessive ducking gain, as this might truncate the beginnings and endings of musical phrases. Use the Ducking On/Off toggle to quickly assess the results.
Problem: PSE is inserted on a vocal channel, but a snare drum is bleeding into the vocal mic, preventing PSE from lowering the vocal gain between sung phrases.
Solution: To prevent this interference, route the snare channel into PSE’s external sidechain input. Switch to EXT Source and turn Ducking on. Adjust the delay settings so that the direct sound arrives at the same time as the sound bleeding into the vocal mic. Delay units can be displayed in meters, feet, or time (in milliseconds). If, for example, the snare is located six feet away from the vocal microphone, set Delay Units to FEET and adjust Ducking Delay to “6.”
When routing multiple sources to the PSE sidechain input, set Ducking Delay according to the closest source. For example, if the electric guitar and the snare are bleeding prominently into the vocal mic, route both instrument channels into PSE’s Side Chain Input. If the electric guitar is physically closer to the vocal mic, set Ducking Delay to the distance between the guitar amp and the vocal microphone. If the snare is closer, set Ducking Delay to the distance between the snare and the vocal mic.