Apogee Symphony 32 User Manual page 13

Symphony 32 PCI card – User's Guide
Maestro Mixer
An Overview
Before describing the functions of Maestro's Mixer pane, a bit of background information concerning latency
and computer-based digital recording setups will help to better understand these Mixer functions.
When recording with most computer-based digital audio applications, the delay between the input and output
of the recording system often disturbs the timing of the musicians who are performing. This delay, known at
latency, means that the musician hears the notes he produces a few milliseconds after having produced them.
As anyone who has spoken on a phone call with echo knows, relatively short delays can confuse the timing of
any conversation, spoken or musical.
To illustrate the effect of latency, figure A depicts the typical signal path of a vocal overdub session. A vocalist
sings into a microphone, which is routed to an analog to digital converter, then to the audio software applica-
tion for recording. In the software application, the vocalist's live signal is mixed with the playback of previously
recorded tracks, routed to a digital to analog converter, and finally to the vocalist's headphones. A slight delay
accumulates at each conversion stage, while a much greater amount of delay occurs through the software ap-
plication, resulting in the vocalist hearing his performance in the headphones a few milliseconds later.
Figure 1
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Figure A
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Symphony 32 PCI card – User's Guide
Maestro Mixer
An Overview
By routing the hardware input directly to the hardware output and mixing in playback as shown in Figure B,
it's possible to provide the vocalist a headphone monitoring signal with a much shorter delay.
First, the signal being recorded (in this case, a vocal mic) is split just after the A/D stage and routed to both
the software applicaton for recording and directly back to the hardware outputs without going through the
latency-inducing software; this creates a low latency path from mic to headphones. Next, a stereo mix of play-
back tracks is routed to the low latency mixer and combined with the hardware input(s). This allows the per-
former to hear himself without a confusing delay while listening to playback tracks in order to record overdubs.
Note that the software application's mixer is used to set a stereo mix of playback tracks while the low latency
mixer is used to set the balance between the stereo playback mix and the hardware inputs.
Figure 2
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Figure B
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