[PD] jack periods 32 = no pd

[Miller Puckette]

OK... that's really quite strange indeed.  FWIW the 'mmap' alsa code, as
far as I know, is only selected for RME devices.  I don't have any of those
handy so have little way to check any of this on my end.  It was written by
Winfried Ritsch a decade or more ago :)

Miller

> 
> Made a latency test with pd's own latency testing patch 
> /usr/local/lib/pd/doc/7.stuff/tools/latency.pd
> 
> -alsa -rt -audiobuf 2 -channels 18 on an HDSPe card with Multiface and
> a loopback analogue cable gives 6.5ms, which I consider great!
> 
> Interestingly Pd gives this latency value regardless of setting
> -audiobuf to values 1-6, which I suppose is because of rounding this
> value to something usable by the dsp part. Pd also reports on startup
> "...buffer_time 2902 us opened"
> "using mmap audio interface"
> 
> Now what is weird, is that I can't get clean audio under alsa with any
> values larger than -audiobuf 6. The sound is very distorted.
> 
> Using the -oss emulation and -rt, clean audio is available for values larger
> than -audiobuf 2 such as:
> 
> -audiobuf 3     with measured latency of 7.9ms (Pd choses blocksze 56)
> -audiobuf 5     with measured latency of 9.4ms (Pd choses blocksze 56)
> -audiobuf 6     with measured latency of 10.9ms (Pd choses blocksze 56)
> and so on.
> 
> Oh this is on a Debian system running kernel 3.2.0-4-rt-amd64
> 
> Nice that Pd can do so low latencies, but that's a strange thing about alsa though...
> > 
> > best, P
> > 
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