[PD] 3d sound with 2 speaker

[julien.breval at tremplin-utc.net]

hello

I'm not a specialist of the Doppler question (last month I experimented a lot 
around the idea of suppressing it in delay lines or when changing audio chunk 
sizes in realtime), but some time ago I had to make a stereo-version of a 4-
track tune for putting it on a normal CD.

The final solution I chose was very simple :
* the left / right panoramic repreasents the X-axis as usual
* for the Z-axis ("depth") I used two crossfading filters (lowpass and highpass 
with a weak quality factor)
This doesn't apply any Doppler effect but at least you *may* feel like in a 2D 
space.
Before doing this, I tried to use the Doppler effect, so here is my report 
about this.

The actual Doppler effect can be produced by a variable time delay line (use 
[vd~] in Pure Data). When the delay time decreases, the pitch raises ; on the 
contrary, when you increase the delay time, the pitch falls down. This works 
basically the same way in the everyday life, like when a car comes from the 
distance, then passes in front of you and finally and disappears in the 
(opposite) distance. On a computer, you can also add some feedback for 
exaggerating this (tunnel-like effect ?).

This is a solution I implemented (quite simplist I admit) :

* the left/right pan is still controlled by the displacement of the source over 
the X-axis ("width")

* the delay time is controlled by the displacement of the source over the Z-
axis ("depth"). Actually, Z had its range between 0 (the closest) to 1 (the 
furthest). I added a (Max)[scale]-like function to set the lowest delay time 
limit (when the source is "close"), the highest time (when the source is "far") 
and the curve of this scale conversion (linear, exp, etc). THe properties of 
the "space" in which your sound moves are only determined by these three latter 
parameters.

It's not very realistic, but 
-> at least you get a similar Doppler effect
-> computers don't have to be stuck into reality like this
-> you can consider it as an abstract space that you define yourself

Normally, the Doppler effect is related to the speed of displacement and to the 
distance from which you hear it. If you find the right equations, you can 
implement it with [expr] or something similar.


Some other solutions :
* using phase inversion (multiply the signal by -1 for example)
* using the Doppler VST plug-in from GRM Tools


I don't know if it helps, but good luck with this

-j

Selon pun chik <punchik at fastmail.fm>:

> 
> 
> hi, do anybody have tried creating doppler effects with pd? i was
> wondering if there is any external or abstraction, etc to  create a
> surrounding effect within a stereo field. id like to create a patch
> using 2 speakers where a sound (an insect) flyes around you. any
> hint????
> 
> 
> bye
> 
> punchik
> -- 
>   pun chik
>   punchik at fastmail.fm
> 
> 
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