Technical information

Apollo Software Manual Chapter 11: Latency & Apollo 181
Latency Basics
Latency (delay) is an inherent factor in digital audio systems because of A/D-D/A conver-
sion, I/O buffering in the DAW, plug-in signal processing, and other aspects.
Although there are ways to mitigate latency (such as delay compensation and/or low-la-
tency monitoring), it always exists to some degree when working with systems that com-
bine analog and digital audio. These concepts are explained in greater detail below.
Audio Interface Latency
Every audio interface that performs A/D and/or D/A conversion induces latency as a result
of the conversion process. This inherent A/D–D/A latency is essentially undetectable.
A/D–D/A latency usually depends on the sample rate, with higher sample rates inducing
less latency (higher rates = less time required for conversion).
An audio interface’s “analog I/O round-trip latency” specification refers to how long it
takes for an analog signal at an interface input to reappear at the same interface’s analog
output after both A/D and D/A conversion. Apollo’s audio interface analog I/O round-trip
latency is 1.1 milliseconds at a sample rate of 96 kHz.
Console Mixer Latency
Apollo’s Console Mixer is used for low-latency monitoring (cue mixing) of Apollo’s analog
and digital inputs. Using Console to monitor Apollo’s inputs may or may not add to the
inherent analog I/O round-trip latency, depending on how it is configured:
Console without UAD plug-ins – When Console is used without UAD plug-ins, monitor-
ing Apollo’s inputs via Console does not add any latency. In this configuration, Apollo’s
analog I/O round-trip latency is still 1.1 milliseconds at 96 kHz.
Console with Realtime UAD Processing – When Console is used for Realtime UAD Pro-
cessing with UAD Powered Plug-Ins that are not upsampled, monitoring Apollo’s inputs
via Console does not add any latency.
In this configuration, Apollo’s analog I/O round-trip latency is still 1.1 milliseconds at 96
kHz, even if up to four UAD (non-upsampled) plug-ins are serially “stacked” (chained) on
a single Apollo analog and/or digital input.
Multiple Apollo inputs can have up to four UAD (non-upsampled) plug-ins each (up to
the limit of available DSP resources); this configuration also does not add any latency.
Note: Upsampled UAD plug-ins add latency when used in Console or a DAW. See
Upsampled UAD plug-ins below for details.
Console Auxiliary Buses – The outputs of the auxiliary buses in Console have 32 samples
of additional latency. This is necessary to maintain the lowest possible input latency.