On Sun, Jun 17, 2012 at 1:34 AM, Simon Wise <[email protected]> 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. Matt _______________________________________________ [email protected] mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
