[RossBencina]

Nice. To the folks saying "nothing to see here" this appears to be a variation of filter-bank spectral analysis where each band varies in frequency to track "the" in-band sinusoid. Somewhat like a bank of PLLs each with its own tracking bandpass filter. By using IIR filters rather than FFTs you avoid the latency of buffering up a full frame of data before you can run the FFT analysis. I am curious how this handles input containing broadband transients. It might be interesting to use CIC filters rather than an IIR lowpass to get better time selectivity, but maybe that's already been addressed, I didn't read the papers.

[arjf]

I used the Exponentially Weighted Moving Average (aka low-pass filter) because it has a very nice iterative form and is very computationally efficient. My objective was low-latency for real-time systems (so no looking into the future either). I haven't looked into using other types of filters because I haven't felt the need for my own applications.

Also my primary objective was tonal analysis so that's where I focused my limited time and resources.

I haven't had time to explore what to do with broadband transients much. A tracking resonator bank will certainly capture the energy (either in tracking mode or not). To me the synthesis examples I have posted on the project site sounds very comparable to traditional vocoder results; not bad but not great, especially with transients (as expected...)

From an analysis point of view, I anticipate that a Novelty measure computed from a tracking resonator bank would be quite usable...

[RossBencina]

CIC filters also use a simple efficient recursive algorithm: just an accumulator and a delay line. No built-in frequency selectivity. https://www.dsprelated.com/showarticle/1337.php

Agree re transients. I think Miller Puckette's "bonk" object did transient detection using filter bank. Can't find the paper right now. In general I think detecting rapid changes in phase performs better than changes in amplitude for transient detection.

I believe that the good sounding phase vocoder algorithms do transient detection and instantaneously reset the phase of the spectral peaks associated with the transient (effectively passing through the original transient without smearing it).

[arjf]

Thanks - adding all of that to my to read / to do list :-)