[PD] [delwrite~], or "what Pd operations are/should be realtime?"

Jonathan Wilkes jancsika at yahoo.com
Wed Nov 23 20:12:03 CET 2016

> I don't know about average, but I have heard "longest delay I use is maybe 30-60 seconds" a few times.
In a case where the user wants a "clear" method that works in realtime without dropouts?

> The bass piece I presented at PdCon has up to 30 seconds of delay for a complex mensuration/transposition canon, and it would be very useful to be able to clear it for rehearsal purposes.
When the performer stops, do you want the DSP graph to continue unabated?  Or could you ramp down and duck out of dsp computation to trigger the "clear" method?

On Wed, Nov 23, 2016 at 12:35 PM, Jonathan Wilkes <jancsika at yahoo.com> wrote:

> In this case, I'd probably rather see a hybrid approach where a second buffer is already waiting. Then you could give "clear 300", and it would switch to the empty buffer immediately while guaranteeing that the other one is clear in 300ms. But this is maybe too complicated for the user, and uses too much memory?

Matt,In the user reports, what is the average size of the buffer?  Are we really talking about buffers greater than, say, 1000ms?
This sounds like premature optimization to me.

On Tue, Nov 22, 2016 at 7:32 AM, Ivica Bukvic <ico at vt.edu> wrote:

For clear, I can imagine having a second empty memory buffer being created while delay continues to use the populated one until the memory allocation is complete. At that point a simple change in the pointer should suffice, after which the old buffer gets trashed. This would break determinacy, so perhaps a separate argument could be used to enable this option in which case the object could get another outlet that sends a bang when the procedure is complete.Best,-- 
Ivica Ico Bukvic, D.M.A.
Associate Professor
Computer Music
ICAT Senior Fellow
Director -- DISIS, L2Ork
Virginia Tech
School of Performing Arts – 0141
Blacksburg, VA 24061
(540) 231-6139
ico at vt.edu
On Nov 22, 2016 00:07, "Matt Barber" <brbrofsvl at gmail.com> wrote:

Hi list; thanks for a wonderful PdCon (to Stevens and NYU people especially).
I had a quick chat with Miller after the "future of Pd" discussion. I told him there is one feature I've heard Pd users ask for many times: a "clear" method for [delwrite~]. A [delwrite~] resize method is something I've heard brought up a number of times as well, but I didn't mention it.
Each of these has a runtime cost that could disrupt the realtime dsp calculation. Clearing a [delwrite~] is a linear-time operation, and for long delay lines it could cause audio dropouts; resizing is more problematic because it's not clear what to do with samples already in the delay line – probably it would need to be cleared as well, which would take even more time (although there is already an indirect resize function when sample rate is changed).
On the other hand, Pd arrays can be resized and cleared (const 0) ad libitum, which is more or less the same operation. We usually tell users 'do this at your own risk when computing audio.'
So what is the main difference? I think it's that [delwrite~] is a tilde object that is supposed not to cause dropouts on its own. If clearing it could cause a dropout, there are reasons for thinking of that as a bug rather than simply a risk.
Is there a compromise procedure? We could add an option to spread the clearing out over time. For instance "clear 5000" would mean "clear the delay line over the next 5000 ms." A second argument would let the user choose whether to preferentially preserve the most recent samples or the oldest samples. Given only a time argument, default would be to preserve oldest samples (less work has to be done overall since the write pointer would also be filling the line with zeroes). Without a time argument (i.e. "clear" with no arguments), the default would be to clear it immediately with the understanding that there could be a possible dropout.
A broader topic for another time would be "what Pd operations are/should be realtime, and which are best at load time?"
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