[PD] ipoke~ ?

Matt Barber brbrofsvl at gmail.com
Sun Jun 17 16:52:51 CEST 2012

On Sun, Jun 17, 2012 at 1:34 AM, Simon Wise <simonzwise at gmail.com> wrote:
> 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.

Yes, good points, and thanks. But it does make a fun "what if" -- I
guess my scenario is more literally like a write head moving toward a
read head faster than the speed of the tape. You're right that it's an
utterly different medium than air.


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