Problems with delays and feedback loops (FV-1/SpinCAD)

Started by Digital Larry, March 31, 2021, 11:17:02 AM

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Digital Larry

I started using SpinCAD again for the first time in years and stumbled across a common problem.

Sometimes when you have a delay with a feedback loop, the sound will disappear suddenly or gradually.  This happens with either the simulator or the actual chip.  I haven't put it on a scope to see what is happening but I believe this is due to DC offset building up and then the output gets slammed into one of the rails and can't recover.

A simple way to avoid this is to put a 1-pole high pass filter into the feedback loop.  That blocks DC and prevents the problem and only costs two instructions.  Four if you don't optimize the inter-block connection.
Digital Larry
Want to quickly design your own effects patches for the Spin FV-1 DSP chip?