Avoiding Feedback Loops
1212 I/O Website
Contents
Sound Manager programs (MacOS)
Feedback on startup, or when digital audio programs aren't running
General Information
In both analog and digital audio, high-pitched whines are usually due to the inadvertent creation of a feedback loop. We've all experienced the high-pitched squeals of microphone feedback, for instance.
Since the 1212 I/O has both inputs and outputs, and even has a small built-in monitor mixer, it's possible to create a feedback loop when using the 1212 I/O in conjunction with external devices. With just a little care, however, feedback loops can easily be avoided.
Common situations in which feedback loops can be created include:
- Recording to a DAT via S/PDIF
- Recording to an ADAT
- Using the 1212 I/O with a digital or analog mixer
So, how does feedback work? Let's say that you are recording to a DAT via the 1212 I/O's S/PDIF output. The 1212 I/O S/PDIF output is connected to the DAT's input, and the DAT's S/PDIF output is connected to the 1212 I/O's input. This is all fine so far.
If, however, the 1212 I/O is set to route its S/PDIF input to the S/PDIF output, a feedback loop will be created. In this case, the output of the 1212 I/O goes into the DAT, the DAT's S/PDIF output goes back into the 1212 I/O, which then goes back into the DAT again, and so on. This creates a loud, high-pitched whine.
(When working with DATs, feedback should only be an issue when recording. This is because most DAT machines ignore their inputs during playback, which prevents a feedback loop from being created.)
Feedback can conceivably happen whenever a digital or analog audio device is bi-directionally connected to the 1212 I/O. We'll use the term "bi-directionally connected" below; it means that the device's inputs and outputs are both connected to the 1212 I/O.
To prevent feedback, you need to make sure that the digital audio software is not routing an input back to the same output, such as S/PDIF In to S/PDIF Out.
The actual procedure for controlling input-to-output routing will vary depending on the digital audio software being used.
All Software
Record monitoring (also called Input Monitoring) routes audio from input to output, so make sure that a record-enabled channel's output setting does not create a feedback loop.
1212 I/O Utility
When recording to a bi-directionally connected device, make sure that the 1212 I/O's inputs are not routed back to the corresponding outputs. For a DAT, make sure that the 1212 I/O's S/PDIF input is not routed to the S/PDIF output.
Sound Manager programs (MacOS)
Make sure that Input Monitoring is disabled when recording to a bi-directionally connected DAT; consult your software's manual for more details.
Also, to avoid feedback in auto-routing mode, make sure that no feedback paths have been created in the 1212 I/O Utility. Simply pressing Mute All will make sure that no routing is active.
Program-Specific Information
For information on avoiding feedback with specific 1212 I/O compatible software, please click on the links below.
Avoiding Feedback with Cubase VST
Feedback on startup, or when digital audio programs aren't
running
Whenever digital audio programs aren't running - at startup, in the Finder, and so on - the 1212 I/O is in Auto-Routing mode. In this mode, the 1212 I/O will route audio directly from input to output. This is designed so that you can leave the 1212 I/O as part of the ADAT optical loop, and still copy audio from one ADAT to another.
The setup for the Auto-Routing Mode is controlled by the 1212 I/O Utility; you can set the sample rate and clock source, route any input to any output, and set the volume level for each input (or mute any or all of them, if desired).
Since this routes inputs to outputs, it's possible to create a feedback loop. This loop will only show up when the card is in Auto-Routing Mode - such as at startup.
To set the default auto-routing mode setup, which is always loaded at startup, use the 1212 I/O Utility's "Save As Defaults..." command, as described in the 1212 I/O manual.
After startup, the Auto-Routing Mode always uses the most recent settings from the 1212 I/O Utility.
If you are getting feedback in Auto-Routing Mode, the simplest way to stop it is to mute all of the inputs. Once the inputs are muted and the feedback is stopped, you can track down the actual cause of the feedback loop, and then set up Auto-Routing Mode again as desired.
Copyright 1998-2000 Korg Inc. FAQ Version: 11/29/00