User Manual

CHAPTER 21. LIVE AUDIO EFFECT REFERENCE 286
cise, and so works well for limiting tasks where you need to ensure that there are absolutely
no signals over the set threshold. RMS is closer to how people actually perceive loudness
and is usually considered more musical. Opto mode, because of its non-linear release
time is often considered smooth and natural sounding. Opto compressors are commonly
used on vocals, bass and electric guitar. But as always, when it comes to compression, trust
your ears and not the meters!
In addition to the EF modes, Compressor offers three Model types that offer further options
for how the device measures and responds to signal levels. FF1 and FF2 are both feed-
forward models, which analyze the loudness of the incoming signal. These are the models
used in the former Compressor I and Compressor II devices, respectively. FB is a feedback
model, which analyzes the output of the device and then self-adjusts its compression be-
havior. Because feedback compressors analyze signals that have already been compressed,
their Attack and Release parameters are a bit less precise, and act more like suggestions to
the compressor. But feedback compression generally results in a much smoother sound,
with less overall gain reduction but also less potential for distortion artifacts. The classic
analog compressor models that are so highly sought after in hardware-based studios are
generally all feedback models. Note that, for reasons of quantum physics, Lookahead and
external sidechaining are disabled when using the FB model; Ableton's engineers are hard
at work developing code that will allow our software to predict the future, but we don't
anticipate having this available until at least the next major release.
21.5.1 Sidechain Parameters
The Compressor Device
With Sidechain Section.
Normally, the signal being compressed and the input source that triggers the compressor