[PD] Zen Garden re-implementing the wheel in C++?

Tim Blechmann tim at klingt.org
Sat Apr 17 15:04:00 CEST 2010

unfortunately, this is not a trivial issue.

dynamically changing the signal graph is possible (actually, i had an 
implementation of that in nova). do the topological sorting in the 
background and you are fine.

the tricky part are implicit dependencies. see this trivial patch:
|send~ foo|

|receive~ foo|

it execution order is ambiguous. either (a) adc-send-receive-dac or
(b) receive-dac-adc-send. the actual execution order depends on the 
implementation. the case (b) introduces one sample block of latency between 
send and receive, (a) doesn't introduce any latency.
without the loss of generality, lets assume that the actual order of the dsp 
graph is (b). now you add a connection between adc~ and dac~. the 
topological sorting of the dsp graph may come to the execution order (a). 
adding the connection, you change the layout of the signal graph, changing 
the order of send~ and receive~ and therefore its semantics. you actually 
loose one sample block and therefore have an audio dropout.

if there are any possibilities to circumvent this issue, i haven't found 
any. for special cases, it works, but whenever implicit dependencies have to 
be taken into account, things are getting very messy. if you want to have 
dynamically changing signal graphs, don't use max-like languages. it is not 
a problem of the implementation, it is a problem of the programming model in 
general! if you need dynamically changing signal graphs, you should use a 
system, that is designed for this use case.

cheers, tim

> Yes. This was a design goal from early on.
> A dynamically rewritable signal graph is
> quite essential to advanced procedural audio.
> On Sat, 17 Apr 2010 12:04:09 +0200
> Tim Blechmann <tim at klingt.org> wrote:
>> > I'm excited about the idea of a more object-oriented approach, and
>> > especially with the idea of ditching all the Tk/Tcl garbage, but I
>> > don't really see the utility of re-implementing all the DSP graph
>> > code.
>> depending on their implementation, it may be possible to do click-free
>> changes of the dsp graph, which is the weakest part of the dsp engine of
>> pd. from my understanding impossible to fully eliminate audio dropouts
>> when changing max-like signal graph, since the implicit resource access
>> order may change, depending on the use case.
>> tim

tim at klingt.org

Happiness is a byproduct of function, purpose, and conflict; those who
seek happiness for itself seek victory without war.
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