Hi team
I have begun my research into FFT processing in PD and have encountered a fairly simple problem I cannot yet solve, can you help? Using [delread4~] I am filtering [noise~] with delay times <10ms and I can hear the expected effect, but cannot SEE it. I suspect there is a naiive error in either my fft or in my array proerties. many thanks

plotting spectrum of FIR lowpass delay line

A few things:
the comb filtering only happens when you add delayed and nondelayed signals. However, you only have the delayed version going into the fft.Secondly, I didn't know why the biquad filter was there so I removed it, and scaled the graph so the peaks were at the top of the graph.
Thirdly, the array size has to match the block size of the fft. Since the real fft only does half a block, it's only necessary to have the graph go to 2048 in this case
After doing those things you should be able to see it (at relatively high frequencies anyways).

Thank you very much; I look forward to learning from this
Cheers