Audio Mixing Anomalies


I’ve got a audiograph containing AudioSources (adapted to AudioProcessors) feeding into external effects chains as well as midi channels driving VST instruments that can also be fed into external effects chains. The audio coming out of multiple AudioSources effect chains can be directly attached to an audio output node without mixing, but if a VST instrument is attached, a horrible noise, apparently a positive feedback artifact, is produced. The solution is to add a mixer to sum all the sources, but why is necessary to mix a VST instrument, but audio coming purely through VST effects can be connected without mixing?

Note the behavior can be reproduced in Juce’s demo plug in host with 3rd party VST instruments: just add two VST instruments and connect their outputs to the audio output. You must keep the stereo connections, I was able to attach just two lefts or two rights, but two lefts plus two rights cause the noise mentioned in the first paragraph.


Sound like a bug, probably somewhere in the horribly complicated AudioProcessorGraph routing code…


I’ve been wiring together some stuff in the AudioProcessorGraph, and was having trouble getting the sound out, and so I did some patching in the Audio Host.
I have been using my own home made AudioSource/Processor with a midi generating processor where as in these images I am using Sawer (from IL) and the JuceDemoPlugin (JDP)

  1. What I was trying to do in my own graph. If the source generated its own midi, it played.
  2. Right Channel only came through
  3. This worked fine until I fed the left JDP back into the right JDP
  4. If I had the sawer connected to the output with the right channel, then I only got that through (of course) but if I connected any of the other output pins to the right channel, I got the right channel data out of both channels. Weird.

I’m not too bothered at the moment because I’m not keen on doing a patching thing, but a heads up for those who will be interested in doing so. It might be a little tricky!
I’ve only used AudioMulch that can do these sorts of whacked out things (and it was only with audio chains, not midi). I dunno if tracktion will do it, as I haven’t found out.

keep on rockin’!