so really the patch is more complex than it needs to be (imo), as it allows a bit of tuning, the essence of the patch is...
the way the patch works is, it sends the audio out and back in, and writes to a delay line,
then the incoming audio is subtracted from the delayed audio.. so theorectically if the delay time is the same as the physical delay, it will result in zero i.e. a flat line.
the first complication is, this only works if the gain level is identical, below I posted it a bit, and then used a *c to reduce it a bit.
(if the gain is wrong, you'll see a copy of the waveform or inverse, as the negation is not complete)
in practice, you'll notice the negation doesn't quite result in zero, there is still some signal left, id assumed this was noise but I'm nnow ot convinced of this.
the frequency of the oscillator theoretically shouldn't matter, but in practice it does, you can see we start getting an offset at higher frequency, my assumption is this is because the sensitivity of either the ADC or DAC changes with frequency