Stereo and Mono Sidechain Compressors for Tracktion

OUTPUT LEVEL dB

The Contour Edit Screen

 

Threshold

0

 

 

 

 

 

 

 

 

 

 

 

The level at which the compressor starts work-

 

 

 

 

 

 

 

 

 

 

 

ing is called the threshold. The compressor will

 

 

 

 

 

 

 

 

 

 

-6

 

 

 

 

 

 

 

 

 

 

 

reduce the level of signals above the threshold

 

 

 

 

 

 

 

 

 

 

 

volume level and not affect lower-level signals.

 

 

 

 

 

 

 

 

 

 

-12

 

 

 

 

 

 

 

 

 

 

 

You can adjust the threshold by grabbing the T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

node on the graph, or by adjusting the slider.

-18

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-24

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-30

 

 

 

 

 

 

 

 

 

 

 

The threshold has been set here to –30 dB, so

 

 

 

 

 

 

 

 

 

 

 

-36

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-42

 

 

 

 

 

 

 

 

 

 

 

any input levels lower than –30 dB are not af-

 

 

 

 

 

 

 

 

 

 

 

fected by the compressor. For example, an input

 

 

 

 

 

 

 

 

 

 

-48

 

 

 

 

 

 

 

 

 

 

 

signal of –42 dB has an output of –42 dB, (as-

 

 

 

 

 

 

 

 

 

 

 

suming no Makeup gain has been added).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-48 -42 -36 -30 -24 -18 -12 -6

0 End Point

INPUT LEVEL dB

This interactive graph does not show the actual input or output signals dancing across the screen. It shows the contour we can apply to the compressor to make it work as we want it to. It's a bit like a Jello mold, it's shape affects the shape of the Jello.

You can adjust the End Point by grabbing the E node on the graph, or by adjusting the slider.

The End Point shown here, is set to an output level of –18 dB.

The input signal level in dB is the horizontal axis, and the output level is the vertical axis, with 0 dBfs at the top, and –48 dBfs at the bottom (dBfs = dB full scale).

If the compressor did nothing to your signal, then the contour curve would just be a straight diagonal line, going from bottom left to top right (input=output).

The example above shows a simple set up, with just the Threshold (T) and End Point (E) in place. Further nodes can be added between the threshold and end point, to really make things fly. See the Node Editing section on page 19.

Any input signals higher than the threshold will be attenuated by an amount determined by the slope of the graph. For example, if the input level is –12 dB, follow the –12 dB line vertically until it hits the line joining the T and E nodes. From there, follow horizontally to the left, and read the output level (approx –23 dB).

As a test, sit up straight, get a 2B pencil and fill in the output levels for the following input lev- els, from the graph:

Input Level dB

Output Level dB

0

–6

–12–23

–18

OK, sorry about the test there.

User’s Guide

17