[PD] Audio latency on linux

[Christof Ressi]

Hi,

> I found it: The delay setting in the audio settings is the culprit:
> It was set at 25 ms and setting
If you want to reduce latency even more, try to enable "callbacks" in 
the audio settings (or start Pd with the "-callback" option). Generally, 
this is not recommend, unless you really need the lowest possible latency.
> I even tried to compile pd with a lower blocksize
To anyone reading: don't try this at home!

Christof

On 10.05.2023 19:04, Orm Finnendahl wrote:
> Hi,
>
>   for a project involving controlled and tuned feedback through the
> Audio Interface, we need very low latency (~ 9-10 ms roundtrip through
> the analog ins/outs) for it to work properly. We did some tests using
> OSX and linux based systems with different audio interfaces.
>
> On OSX I can get down to 16 ms with pd (44.1 kHz sr); using Max/MSP we
> can get below 10ms with a vector size of 32.
>
> On Linux the lowest I can get with pd is 29.33 ms with 48k samplerate
> (this is using alsa; jack is ~34 ms).
>
> jack_delay reports a 9.6 ms roundtrip delay through the analog outputs
> with a vector size of 64, so it is not the driver and in principle
> should be possible to get a lower latency in linux. I don't know if
> jack_delay is implemented with additional i/o buffers but even if pd
> adds an extra period in both directions that should be well below 30ms
> (64 samples are 1.33 ms at 48k). The added 20ms in comparison to
> jack_delay appear quite large to me.
>
> I even tried to compile pd with a lower blocksize (I changed
> DEFDACBLKSIZE in s_stuff.h and DEFSENDVS in d_global.c and can get
> down to a vectorsize of 32 without distortion at the audio interface),
> but that doesn't change the i/o latency at all. I didn't yet study the
> alsa/jack related code.
>
> Can anyone shed a light on this? It'd be much nicer to use pd for this
> than writing a dedicated app doing all the dsp (or using Max/MSP on
> OSX :-(
>
> --
> Orm
>
>
>
>
>
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