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@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@fastmail.fm

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