Side-Chain - what it is and what it isn’t, Part 2

  • 09/24/2013
  • Michael Krusch
  • Story
  • Basics
  • Compression

What you think it is

Despite the broadly spread opinion, we are plainly referring to the separate side-chain input of the compressor, and only such compressors do have a side-chain, this building-group is to be found in all compressors.

What it really is

The term comes from the internal signal-flow of the compressor and terms what led to the actual main-signal-way the paralleled signal-way for the creation of the control-signal.

Merely the input signal of this building-group is selectable with the devices with separate side-chain input and does not necessarily need to be the signal that is to be worked on.
It is theoretically possible to inject every signal, to define the control of the control amplifier, as long as it lies within the right level-reach. The main function of the side-chain is to gain a control-signal from the input signal for the control amplifier. As a general rule the audio-signal itself, which is to be processes, is used. Through the level-progression of this signal, there is a voltage created, which directs the amplification of the main signal-way-the control voltage.

How it works

The processing is not always identical, because the building-group that is used to influence the signal-level is not always identical. The way of the control amplifier is principally giving the direction on which lead-signal is used, thereby determining its processing.

The provided illustration is therefore only providing the general principle. The side-chain can vary depending if it is aimed at a tube, photoconductive resistors, field-effect transistor or a VCA. The function-building-group, however, can be found almost everywhere.

PAs a principle one can divide the side-chain into an amplifier, rectifier and Integrator. Often one also finds a more or less variable filter for the interjection of the frequency of the lead-signal (mostly at the entry) in the side-chain. Through the entry-amplification of the side-chain, the degree of compression- the ratio is set. The misalignment of the voltage is added to the amplified signal. This leads to it setting the threshold at which the compression starts.

The rectifier that follows after ensures that the AC signal is turned into a unipolar signal. Attack and release are set via a resistor and capacitor network mostly in combination with the operational amplifier. The shifted and equalized voltage is used for the charging and discharging of the condenser.

With a set size of the condenser the variable resistances (attack and release potentiometer) determine through which the charge- and discharge-streams flows, the time that passes, up until a certain condensation-voltage is set. She kind of rushes behind the entry-voltage-progression and is responsible for the deformation, more precisely the “straightening” of the lead-signal.

The thereby created signal is finally added to the control amplifier in the main-signal and guides the whole amplification-process.
Falls du Teil 1 und Teil 3 unseres Side-Chain-Spezials noch nicht gelesen hast, hole es unbedingt nach.
Side-Chain - what it is and what it isn’t, Part 1
Side-Chain - what it is and what it isn’t, Part 2
Side-Chain - what it is and what it isn’t, Part 3