Using Signal Processors
The Difference between Signal Processors and Effects
Unlike effects, which are creative in nature, signal processors are used to control and manipulate sounds to achieve the best audio quality performances and recordings. Effects and signal processors should never be confused.
Whereas effects are “mixed” with an input to provide a combined sound, signal processors alter an input, group or mix signal completely. The signal is actually taken out of the mixer entirely, “processed” and returned in its altered state, in series with the original audio signal.
For this reason signal processors should be connected using Insert Points and not the Auxiliary Send and Return Loop (effects loop).
NB: Effects can be connected to inserts if necessary, but then the proportion of the effect in the signal is governed solely by the effects unit mix control.
The Different Types of Signal Processors
Broadly speaking, there are 5 different types of signal processor in common use:
Graphic Equalisers
Graphic Equalisers work by splitting the sound spectrum into narrow, adjacent frequency bands and giving each band its own cut/boost slider. The term Graphic comes about because the position or ‘curve’ of the sliders gives a graphic representation of the way in which the settings affect the audio frequency range.
Graphic Equalisers are most often used to process the mix at live venues by notching out troublesome frequencies that may be causing feedback. They may also be used to enhance a mix at a poor sounding venue. In recording they are used to create "flat" listening environments.
For more detail on venue acoustics go to section 4 - PA Mixing.
Parametric Equalisers
These are similar to the EQ found on an input channel but may include more bands and additional bandwidth (Q) controls which define how many frequencies in the band are affected.
They are most often used to provide additional creative control over an input signal when a mixer’s EQ is not sufficient.
Gates
A gate is designed to shut down the audio signal path when the input signal falls below a threshold set by the user. It may be used to clean-up any signal that has pauses in it. For example gates are widely used to prevent ‘spill’ between adjacent mics on a multi-mic’d drum kit where, say, a tom-tom mic may pick up the snare drum.
Expanders
Expanders accomplish much the same task as gates, though they are more like compressors in reverse. Compressors affect the gain of signals exceeding the threshold, while expanders act on signals falling below the threshold. A gate will close completely when the signal falls below its threshold, but an expander works like an automatic mixing engineer who pulls down the signal when the signal falls below the threshold; the more it falls below the threshold -the more he pulls down the fader.
Expanders are most often use in Studio recording to provide the best mix signal to noise ratio when producing final masters.