[PD] Weird issue: need to increase Pd latency in FFT patches, otherwise Pd sound output glitches and clocks are slowing down!!!

Christof Ressi christof.ressi at gmx.at
Mon Oct 31 14:38:16 CET 2016


I have the following issue with Pd 0.47.1 on Win 7 (onboard soundcard + ASIO4ALL and also Focusrite Scarlett 6i6 + Focusrite ASIO Driver):

When I use more than just a few FFTs anywhere in my patch, I get a staggering sound output + clicks from Pd unless I increase the Pd latency... Apparently, it's only the playback because I couldn't hear it in a recording I made with [writesf~]. Therefore I made a recording in Reaper to show you what I'm hearing.

The more FFTs and the larger the FFT blocksize, the larger I have to set the latency. This even happens if the CPU load is as little as 5% (where 25% would be the maximum for one hardware thread on my laptop). 

In my test patch, I put a couple of FFT subpatches and a single sine wave with a volume control to check the sound output. Usually, I can play a sine wave without artifacts as long as the CPU load is not peeking. But here, the FFTs seem to magically disturb the audio output of the whole patch...

I think there's something going wrong with the scheduler because also objects like [metro] and [line] start to go slower - sometimes up to 50%!

What is going on!?

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