Yep, this should not be a patent..It's a trivial solution to the problem that could be devised by any sound engineer!

If you have any evidence of prior work to that patent (I really hope you do), then you can topple that patent. If your code to do what you said isn't free software I'd recommend you release it as free software now.

I can't check right now, but it's possible that the patent predates my use of the technique. Even if not, I don't know how I could prove it.

By the way, it wasn't done in code; I did it manually in Ardour [0].

[0] <https://ardour.org/>