SSL Mixer Manual - Absolute Professional Audio

Automatic Delay Compensation (ADC)
In a digital mixing system, any processing of an audio signal takes a certain amount of time, known as a processing delay.
When several signals are processed in parallel (for instance a kick drum going through a compressor in a mixer column and a
bass going through a compressor, an EQ and a chorus in an other mixer column), the cumulated processing delay for each
signal may be different, resulting in "misaligned" audio signals. Phase problems may also be created.
These problems can be solved by introducing compensating delays in some of the signal paths as necessary to get the output
audio signals perfectly aligned. However, this introduces another problem: since all the signals must be aligned with the
"slowest" one (i.e., the one that sustains the highest cumulated processing delay), any signal going through the system is
delayed, either by a processing delay or by a compensating delay.
Therefore, a performer cannot monitor his/her performance in real-time through that system The overall delay is perceived as
the inherent "latency" of the system.
A benefit of DSP-powered systems such as MX4 and Mixpander is that the processing delays are in most cases negligible,
comparable to those of hardware digital mixers and effects units.
In fact, MX4 and Mixpander are indeed hardware systems, controlled via a software interface.
On the other hand, native systems that use the CPU of the host PC are subject to higher processing delays inherent to the PC
environment, which requires the use of buffers for reliable audio processing, even for the most basic effect plug-in.
VST compatibility offers SSL Mixer users a very wide choice of plug-ins. However, since VST plug-ins inserted in the SSL Mixer
run on the CPU of the host PC, buffers must be used. The Automatic Delay Compensation takes care of the resulting alignment
and phase problems.
Note that in recording situations, when real-time monitoring of the input signals is required, it may be preferable to use only
DSP-powered plug-ins, with or without Automatic Delay Compensation.
VST plug-ins can then be used when mixing, preferably with Automatic Delay Compensation active.
The Automatic Delay Compensation (ADC) function can introduce compensating delays in the Mixer in order to counter the
effects of any mixer element and bus delays.
The ADC compensates for all bus and output delays. This means that the audio paths leading to common points are "lined
up" (i.e., they present the same overall amount of delay). However, all buses and outputs are not necessarily lined up relative
to each other.
For instance, the following output pairs…:
• MADI1-2 U1, used by the "Output (Stereo)" element in mixer column 1
• MADI3-4 U1, used by the "Output (Stereo)" element in mixer column 2
…are not lined up by default if they have completely isolated audio paths in the Mixer. They will only be lined up relative to
each other if they are referenced by the same send or output element.
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