[PD] Delay circuit feedback DSP error-- only when signal path leaves abstraction

William Huston williamahuston at gmail.com
Tue Feb 25 23:40:36 CET 2020


On Tue, Feb 25, 2020 at 6:14 AM Christof Ressi <info at christofressi.com>
wrote:

> @Dan
>
> As far as I recall, going between abstraction to parent patch via
> inlet~/outlet~ introduces a block delay, hence no error
>
> Dan, correction-- that is the exact circumstance where I *am* getting the
error.
So now I think you are beginning to see why I think it's unexpected,
especially because of additional potential delay of inlet~/outlet~.

Dan also wrote:
> As the error says, you shouldn't create a direct feedback loop with
signal cords.

Let me try to explain again:

*I have taken a WORKING CIRCUIT--*
(a simple stereo delay circuit, with cris-cross L/R feedback
implemented with [delwrite~] + [vd~])

*-- which DOES NOT produce a "DSP Loop Error", *

*pulled a Null (straight-wire) Filter *

*(which had been installed in the feedback path)*
*and moved it externally to the abstraction*
*(up to the parent patch), via outlet~/inlet~,*

*which, if anything ADDS additional block delays, *

*yet this produces "DSP Loop Error". *


*Clearly (the way I see it) *

*the logic behind detecting "DSP Loop Error" condition*
*has a bug.*

*I believe this is a false error,*
*because as I have stated--*
*the circuit HAD been working!*

*All I did was add the potential for additional*

*blocks of delay on the feedback path. *

But you're using [r~] and [s~] which is not the same as direct signal
> connections. The former can act like a short delay line. Please read
> "3.audio.examples/G05.execution.order".
>

Christof, Yes! Exactly!
Added delay should REDUCE the chance of a "DSP Loop Detected"!

Also, believe me, r~/s~ has nothing to do with it.
My original patch was extremely ugly, due to criss-crossed feedback.
I only implemented with r~/s~ to clean up the patch to share.

Thanks everyone!
BH














Christof
> On 25.02.2020 11:42, Dan Wilcox wrote:
>
> As far as I recall, going between abstraction to parent patch via
> inlet~/outlet~ introduces a block delay, hence no error
>
> Third patch is like the second, only the effect has been moved out of the
> abstraction, and into the parent patch. ONLY HERE do I get the DSP loop
> error.
>
>
> Signal loop in a single patch without abstractions = error. Pd has no way
> to read and write to the same signal buffer in the patch at the same time
> *without* some tiny delay.
>
> *The point is the last two patches have (or should have) an identical
> graph! *
>
>
> At the lower level, they don't. What happens if you put part of the path
> inside a subpath which uses inlet~/outlet~?
>
> On Feb 25, 2020, at 11:36 AM, William Huston <williamahuston at gmail.com>
> wrote:
>
> First abstraction, simple stereo delay:  2 delay lines, variable feedback
> L->R, R->L.
>  This *works*, no DSP loop error.
>
> Second abstraction contains an effect in the feedback path. (in my simple
> example, it's just a null wire: In-L passes to Out-L, etc). Again this
> *works*, no DSP error.
>
> Third patch is like the second, only the effect has been moved out of the
> abstraction, and into the parent patch. ONLY HERE do I get the DSP loop
> error.
>
> *The point is the last two patches have (or should have) an identical
> graph! *
>
> It really seems like a bug to me.
>
> I'll upload a test patch a little later.
>
> Thanks,
> BH
>
>
> --------
> Dan Wilcox
> @danomatika <http://twitter.com/danomatika>
> danomatika.com
> robotcowboy.com
>
>
>
>
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