[PD] [PD]spatialization : filter problems

julien.breval at tremplin-utc.net julien.breval at tremplin-utc.net
Thu Oct 30 00:22:55 CET 2003

Selon e skogen <eskogen at usfamily.net>:

> > this latter problem was solved using this technique : adding +~ 1 to the
> signal 
> > before processing and -~ 1 after processing
> > therefore all the sound processing is done with positive-value signals, so
> it's 
> > easy to add or substract some frequencies to the signal    

> i guess i'm not following this, could you send an example perhaps?

Tomorrow it will be possible (currently I don't have any access the Internet
from my home)

Sorry I wasn't very clear saying "adding / removing" frequencies --- I should
have said "modifying the level of some frequencies" of the signal and leave the
other frequencies unchanged (of course the best way is to use FFT filters)

Low shelving (for example) boosts or attenuates the low frequencies without
changing the rest of the signal (on the contrary, a lowpass filter clears all
high frequencies and leave the low frequencies unchanged)   

If you want to attenuate all the frequencies below 340 Hz, for example,
substracting the output of a lop~ filter to the original signal (with "-~")
won't work -- unless you pre-offset and post-offset the original signal so that
all signal will have strictly positive values during filtering.
I don't know it this is the good method, anyway it works ...

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