Avoiding Feedback Loops
OASYS PCI Website
Contents
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 OASYS PCI has inputs, outputs, and a submixer, it's possible to create a feedback loop when using the OASYS PCI 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 OASYS PCI with a digital or analog mixer
So, how does feedback work? Let's say that you are recording to a DAT via the OASYS PCI's S/PDIF output. The OASYS PCI S/PDIF output is connected to the DAT's input, and the DAT's S/PDIF output is connected to the OASYS PCI's input. This is all fine so far.
If, however, the OASYS PCI 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 OASYS PCI goes into the DAT, the DAT's S/PDIF output goes back into the OASYS PCI, 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 OASYS PCI. We'll use the term "bi-directionally connected" below; it means that the device's inputs and outputs are both connected to the OASYS PCI.
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.
Monitor Mixer
The zero-latency monitor mixer routes audio from input to output, so make sure that channel output settings do not create a feedback loop.
If you are getting feedback in the monitor mixer, 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 monitoring again as desired.
OASYS PCI Editor
When bi-directionally connected to a device, make sure that the OASYS PCI's outputs are not routed back to the corresponding inputs. When using a DAT, make sure that the OASYS PCI's S/PDIF input is not routed back to the S/PDIF output.
Copyright 1999-2002 Korg Inc. FAQ Version: 8/19/02