[PD] ipoke~ ?

Simon Wise simonzwise at gmail.com
Sun Jun 17 07:34:38 CEST 2012

On 17/06/12 12:37, Matt Barber wrote:
>>> As far as mixing vs. overwriting is concerned, that actually depends
>>> on what it's trying to model. Overwriting is probably right for a
>>> looper, but mixing is right for a recording of a moving sound source -
>>> and because [poke~] doesn't interpolate it's not an issue (it wouldn't
>>> be useful to model a moving sound source).
>> But 'approach B' condenses 4 read samples into 1 write sample, so
>> basically it does the same as [poke]: writing one sample at a time.
>> There is no need for mixing internally. If you want to mix, it can be
>> done externally. In my view, a Pd object need not internalize
>> functions that can be done externally, unless there is a huge
>> performance penalty involved.
> Here is one use case where mixing as part of the function would be
> useful. Imagine you're trying to model a sound source moving at mach+
> speeds -- let's say it starts 500 meters away from the microphone and
> plays for 3 seconds, and then it moves toward the microphone at twice
> the speed of sound until it gets two meters away, and then (against
> any sensible law of inertia) it turns on a dime and moves away from
> the mic again at .25 the speed of sound.
> Much of the sound it generates after it makes the turn will reach the
> microphone before the sound it was making when it started its approach
> toward the microphone reaches the mic (since the source overtakes its
> own previous sound).

Not so sure that mixing makes sense in this example if you are trying to model 
something physical ... something moving that fast (for your example a bullet 
which is shot out of a rifle then bounces back off something very substantial 
and hard to produce the trajectory you described) would create a sonic boom (a 
conical wave front) rather than a sound reversed in time while it was travelling 
supersonically. You get a kind of 3D bow-wave produced, like a boat in water, 
rather than neat sound ripples following slowly along behind the source in some 
kind of overlapping spherical wave front pattern. So you would not want to mix, 
but rather would need to model the boom followed by the sound produced after the 
slowdown. I don't know how one would model the sound behind/inside the cone 
while the object was still travelling supersonically, but might guess it was 
turbulent and noisy, probably something a bit like the wake of a boat. Also not 
sure what model you would use to deal with sound produced just before the fast 
travel, but where the projectile caught up and the sonic boom disrupted the nice 
spherical wave fronts.

But you might want to do a mix for other reasons.


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