[PD] dance controllers...

Johannes Taelman johannes.taelman at rug.ac.be
Thu Apr 4 17:16:53 CEST 2002

about doppler-sonar~ ...

> >I was rather thinking about transmitting small-band noise to combine
> >motion-sensing with position-sensing.
> yes, that should do it, too.
> one thing I noticed though is that US receivers can be confused by
> loud audio signals. Just clap your hands, and it might take it for a
> returned US pulse. Has wrecked many performances that worked
> perfectly at home, but couldn't handle the louder stage conditions.

Yup. There are several sound sources that produce interfering US: ringing
keys, speech (eg. ssss), clapping hands. I'll try adding a guard-band in the
analysis so that interfering US sounds interrupts the analysis rather than
disturbing it.

Transmitting very "loud" US helps. And this is far easier with sine-waves
than pulses, because a piezo US transmitter resonates a lot.

> >  > my biggest problem with reflective US was always the amount of energy
> >>  I got back from soft objects (like dancers or people in general...)
> >>  which was never enough to make it work reliably for larger distances
> >
> >Try calculating differences between successive echoes.
> I don't see how this helps when the signal is burried in noise.

No, it does not help against noise, but it elimantes reflections from fixed
objects. Maybe averaging the differences between successive echoes does, but
the output will react slower.

> I would be interested over what distance you receive information from
> moving people.

4 meters in lab-conditions is no problem with my current design.

> And are you using the Polaroid transducers, the smaller stuff from
> RS/Farnell, or something else ?

I used a Monacor MCE-2500 electret capsule interfaced to a P48 phantom
powered preamp for the receiver. It serves as a microphone as well. Maybe a
piezo US receiver works better. I don't have the type number of the US piezo
transmitter I use at hand. It's designed for 40kHz US.


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