What is a compressor?

A compressor reduces gain for signals above a user-settable threshold.

ie. It reduces the levels of peaks, opening up more headroom and allowing the overall signal level to be turned up.
This gives the signal a higher average level. Resulting in a sound that is subjectively louder and “punchier” than an uncompressed signal.

A compressor’s 2 most important parameters are the Threshold and the compression Ratio.


Threshold: the threshold slider sets where compression begins. Signals above this setting are controlled by the Ratio parameter.

Compression Ratio: Sets the ratio between the input and output signal.
Eg. With a compression ratio of 3:1 , if a signal above the threshold increases by 3db, the compressor output will increase by only 1db.
If a signal above the threshold increases by 6db, then the output will increase by only 2 db, and so forth.
A ratio of 1 means no compression, regardless of the threshold.

The orange Gain Reduction meter shows how much the gain is reduced at any given moment. The more reduction, the more audible the effect
Eg. a gain reduction above 6db or so might produce the desired loudness, but significantly alters the sound and is easily capable of destroying its dynamic structure.
NB: This is something that cannot be undone in later production steps.

Keep this in mind especially when using a compressor, limiter or sound loudness-maximizing tool on the master channel. Less is often more here.

Because compression reduces the volume signals and opens up headroom, you can use the output control so that the peaks once again hit the maximum available headroom.
Enabling the Makeup button automatically compensates the output level if the threshold and ratio settings change.

Dry/Wet adjusts the balance between the compressed and uncompressed signals.
At 100% only the compressed signal is heard, while at 0%, the device is effectively bypassed.

Attack and Release:

The Attack and Release controls are essential parameters for controlling the response time of the Compressor by defining how fast it reacts to signal input changes.

Attack: How long it takes to reach maximum compression once a signal exceeds the threshold.
Release: How long it takes for the compressor to return to normal operation once the signal falls below the threshold.

Auto release adjusts release time automatically based on the incoming audio.

We will look at Ableton’s native compressor as well as the glue compressor in more detail as well as a few tips and tricks, in another post.

12 June 2015 Audio Fundamentals , , , , , ,

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