[PD] maximum "control rate" in Pd
Alexandre Torres Porres
porres at gmail.com
Sat Mar 14 07:26:33 CET 2015
2015-03-12 19:36 GMT-03:00 Alexandre Torres Porres <porres at gmail.com>:
> since it was mentioned here, what's the behaviour and deal with
> [vnsapshot~]? Cause there's no help file for ir yet.
Made a few tests and saw how snapshot~ only outputs the last saple from an
audio block, and also how vsnapshot~ can output each audio sample...
> 2015-03-12 19:14 GMT-03:00 Charles Z Henry <czhenry at gmail.com>:
> On Thu, Mar 12, 2015 at 5:01 PM, David Medine <dmedine at ucsd.edu> wrote:
>> > @Charles: None of those five sentences is a misconception. When I said
>> > functions' I meant the functions of the form 'whatever_tilde_perform',
>> > the dsp tick function. I see how this might lead to a misunderstanding.
>> Sorry if I was unclear as well. We *are* trying to split hairs here,
>> of course, just to have an accurate description.
>> It's not *all* of the dsp functions. I thought this was unclear and
>> tried to clarify: rather than scheduling them more often, it actually
>> just loops over the sub-graphs multiple times when the block size is
>> low. There is always a parent function which is being run once every
>> 64 samples (the default).
>> > Also, I see that suseconds_t (which is the type of now.tv_usec) is an
>> > integer, as I had previously thought, so I am really perplexed as to how
>> > [delay] can apparently deliver bangs within less than 1us. I would love
>> > someone to explain this to me. It is a small detail and it doesn't
>> > matter in practice, but I am annoyed when my inferences are not correct
>> > especially when I send them to the Pd list!
>> > On 3/12/2015 1:58 PM, Charles Z Henry wrote:
>> >> On Thu, Mar 12, 2015 at 3:18 PM, David Medine <dmedine at ucsd.edu>
>> >>> Yeah, of course. Block size 1 and high sampling rate will make the
>> >>> between control and audio super tight (ChucK does this, for example).
>> >>> will also eat the hell out of your CPU. It's a trade off. This is
>> >>> you start calling all the DSP functions once every 1/192k seconds
>> >>> of
>> >>> once every 1.45ms.
>> >> This last sentence is also a misconception--the dsp tick function is
>> >> called every 64 samples, as commonly defined.
>> >> sys_time_per_dsp_tick = (TIMEUNITPERSECOND) *
>> >> ((double)sys_schedblocksize) / sys_dacsr;
>> >> sys_schedblocksize gets set from DEFDACBLKSIZE
>> >> So, the dsp_tick gets called, and when there is a sub-patch with
>> >> [block~ 1], it loops over the graph generated from the sub-patch 64
>> >> times.
>> >> You'd find this behavior coded with the block prologue and epilogue
>> >> functions.
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