plugdata sets its reported latency to 64 samples by default and appears to tell REAPER about it. REAPER then tries to correct for this latency using its plugin delay compensation scheme. 64 seems reasonable, right? That's what one might expect as overhead just to get signal into plugdata and back out again (e.g. it takes at least one buffer for Pd vanilla to shuttle signal to/from its own [pd~] subprocess).

But that's not what I'm seeing! I made a track that is silent except for a single 1 in the 2nd or 3rd sample, and have inserted a plugdata plugin that connects [adc~] directly to [dac~]. At 64 samples of latency, if I render the track, the output is completely silent. If I change plugdata's reported latency to 0, the output matches the track.

<spooky music/> Um ... wh-wha-what's going on?

What do you see on your DAW? impulse.wav passSignal.pd

I don't have an answer to this question (and can't report other results, since I also use Reaper), but I have to admit that I'd expect extremely low impact on any actual projects where I'd be using Plugdata. Typically one would export a bit of silence at the beginning -- that first empty block from Pd is technically incorrect, but unlikely to be noticed in practice.

Maybe log a bug for it? But if I were Timothy, I wouldn't treat it as a critical bug. (Now, if there were a 64-sample shift throughout, that would be critical.)

hjh

@ddw_music Oh OK, well I redid the test using a 1033.6 Hz sine wave (1.5 cycles/64 sample block) and the result is consistent with a 64 sample shift (i.e. 180 degrees out of phase), plus it goes away when I set plugdata's latency to 0. I'm gonna check on the REAPER forum to see what they say about PDC--maybe the issue is that REAPER assumes a base 64 sample latency for all plugins so plugdata doesn't need to report that portion.

It would still be interesting to see if other DAWs behave similarly. Maybe I have to dig out my old laptop and struggle with Cubase again. 1033.6 Hz sine.wav

BTW, is there a way to set plugdata's reported latency to the host programmatically? I have an FFT resynthesis patch that uses different block sizes. Camomile has that facility.

Update: I think I'm seeing the same behavior in Audacity, but my understanding of Audacity is weak. I also tested an FFT resynthesis patch in REAPER using a 16384 block size and set plugdata's latency to 16320 (16384 - 64) ; that produced the alignment I was expecting. So I'm provisionally declaring that you should set plugdata's latency to the latency of your patch as measured between adc~ and dac~. In retrospect that seems completely obvious, but I was thrown by plugdata's default of 64.