User guide

Chapter 5: Using Pro Tools | Duet 25
Do I need the Pro Tools IO Control Mixer?
The Pro Tools IO Control mixer serves to provide a low latency monitoring mix while recording. Therefore if you’re using Pro Tools
| Duet to listen to iTunes or audio from another program, there’s no need to use the mixer. It’s possible that the latency of your partic-
ular recording system is low enough to be unnoticed. The system latency is determined by the recording software’s buffer setting; if
your computer is powerful enough, it’s possible to set the buffer to a lower value (shorter latency) without encountering clicks and
pops in the audio output. If the latency doesn’t pose a problem while recording, there’s no need to employ the low latency mixer.
To illustrate the effect of latency, Figure 1 depicts the typical signal path of a vocal overdub session. A vocalist sings into a micro-
phone, which is routed to an analog to digital converter, then to the audio software application for recording. In the software applica-
tion, the vocalist’s live signal is mixed with the playback of previously recorded tracks, routed to a digital to analog converter, and fi-
nally to the vocalist’s headphones. A slight delay accumulates at each conversion stage, while a much greater amount of delay occurs
through the software application, resulting in the vocalist hearing his performance in headphones delayed by several milliseconds.
By routing the hardware input directly to the hardware output and mixing in playback as shown in Figure 2, 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 application
for recording and directly back to the hardware outputs without going through the latency-inducing software. This creates a low la-
tency path from mic to headphones. Next, a stereo mix of playback tracks is routed to the low latency mixer and combined with the
hardware input(s). This allows the performer to hear while listening to playback tracks without a confusing delay to comfortably
record overdubs.
Note that the software application’s mixer sets a stereo mix of playback tracks while the low latency mixer sets the balance between
the stereo playback mix and the hardware inputs.
Figure 1. Calculating latency
Figure 2. Lowering the latency