Thanks for the suggestion, Cyrille. I've been playing around with median filters in a different context (spectral processing), but completely forgot about them.
With the variometer, the problem is to isolate very low frequencies (the pressure gradient you want to detect) from DC (constant atmospheric pressure at certain height) and sensor noise frequencies. And you want to see results with accuracy and little delay. In fact it needs a very sharp minimum-phase filter. Maybe a median filter can 'preprocess' the signal in some way. Anyway it gives a new perspective.
Katja
On Fri, Dec 14, 2012 at 1:27 PM, Cyrille Henry ch@chnry.net wrote:
for sensors data, depending of the noise, it can be useful to begin with a median filter. a median on the 7 last sample add 3 sample delay, but often remove lot's of noise.
you can find them in mapping or puremapping libs. cheers cyrille
Le 14/12/2012 11:38, katja a écrit :
Patrick, the barometer sensor samplerate is ~50 Hz and I did the butterworth filter with regular Pd objects, not as external (see attached).
In the Pd patch I modeled sensor noise (resolution 3 Pascal according to datasheet) and pressure gradient, simulating vertical speed through the air. The aim is to get 0.1 m/s accuracy in vertical speed reading. Theoretically, this would be almost possible with the butterworth. But our real sensor has much more noise than 3 Pascal resolution. Therefore I'm still interested in better filters.
Katja
On Wed, Dec 12, 2012 at 6:29 PM, patrick puredata@11h11.com wrote:
hi Katja,
did you ported this filter: https://github.com/lebipbip/le-BipBip/blob/master/filter.c
to an pd external? if yes could you share it? not sure if it would help my situation (noisy accelerometer 1 axis), but i would like to give it a shot.
thx
Pd-list@iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
Pd-list@iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list