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

Dan Wilcox danomatika at gmail.com
Tue Feb 25 11:22:25 CET 2020

As the error says, you shouldn't create a direct feedback loop with signal cords.

I usually use [throw~] and [catch~] for send/receive busses via the rjlib [c_bus], [c_tobus], & [c_frombus] wrappers: https://github.com/rjdj/rjlib <https://github.com/rjdj/rjlib>

Additionally, I've made stereo versions ([c_bus2], [c_tobus2], [c_frombus2]) in my own rc-patches: https://github.com/danomatika/rc-patches <https://github.com/danomatika/rc-patches>

I suppose we are introducing (tiny) relays with every step, but in practice I have never perceived it. Then again, most of what I do does not relay on "sub-2ms" latency. For a large project at work, we have a signal path with 64 channels using throw~/catch~ like: input/soundfile channel -> spatialization -> virtual speaker -> output.

> On Feb 25, 2020, at 9:50 AM, pd-list-request at lists.iem.at wrote:
> Message: 2
> Date: Tue, 25 Feb 2020 03:50:18 -0500
> From: William Huston <williamahuston at gmail.com <mailto:williamahuston at gmail.com>>
> To: Pd-List <pd-list at lists.iem.at <mailto:pd-list at lists.iem.at>>
> Subject: [PD] Delay circuit feedback DSP error-- only when signal path
> 	leaves abstraction
> Message-ID:
> 	<CAAV8_8=Ui0oV-Hi8jBoxM4MDp_+u8atbZ+uQqNQh9R1BODzczQ at mail.gmail.com <mailto:CAAV8_8=Ui0oV-Hi8jBoxM4MDp_+u8atbZ+uQqNQh9R1BODzczQ at mail.gmail.com>>
> Content-Type: text/plain; charset="utf-8"
> Hi, I've built a classic stereo delay using [delwrite~] and [vd~], and L/R
> crossed feedback. This works!
> Now, I want to insert an effect into the feedback path. (many possibilities
> here: add some bitcrush, so each repeat gradually becomes more
> distorted.... or a [hilbert~] type pitch shift, which might create
> something like Shepard tones, etc).
> *This works when everything is within a single patch or abstraction. *
> However, when I try to allow the effect to be external to the abstraction
> (like a SEND/RETURN insert on a mixer), when I try to complete the circuit,
> I get "DSP loop detected".

Dan Wilcox
@danomatika <http://twitter.com/danomatika>
danomatika.com <http://danomatika.com/>
robotcowboy.com <http://robotcowboy.com/>

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