From: Jim Peters (jim_at_uazu.net)
Date: 2001-12-23 12:04:43
JimmyB_101 wrote:
> --- In buildcheapeeg_at_yahoogroups.com, Jim Peters <jim_at_uazu.net> wrote:
>
> >
> > What I'm finding so far is that what I want to do, e.g. shift a
> 256Hz
> > sampled signal up 8 octaves, has been implemented in theory many
> > times, but the detail makes these solutions completely inappropriate
> > for our particular application.
> >
> > (An 8-octave shift (256x) would map 0.2Hz to 51Hz, and 40Hz to
> 10kHz.
> > This seems a fairly good mapping of interesting brain-wave
> frequencies
> > to the audible range, although other shifts than 8-octave should
> also
> > be possible from the same code. I'd like to keep with whole
> octaves,
> > so that the frequencies have a clear relation to the original
> > frequencies, in case that matters).
> >
>
> for one thing, this would seem to bring the possibility of using
> a sound card for A>D back into the picture.
Actually, I was planning on running this on the host computer, not on
the EEG board. You'd need a fairly powerful processor to do this on
the board (206MHz StrongARM?), unless someone can find a *much* more
efficient algorithm.
Also, there are much better ways of getting the data from the EEG to
the computer via the sound card line-in than this, for instance using
amplitude-modulation of a carrier. Because of the nature of a
pitch-shifter, this isn't a nice simple operation, so there will
always be some level of compromise and error. For recording the data,
I would personally prefer a more direct and unprocessed input, such as
a serial, IRDA or USB connection, or an amplitude-modulated carrier to
the soundcard line-in.
Jim
-- Jim Peters (_)/=\~/_(_) Uazú (_) /=\ ~/_ (_) jim@ (_) /=\ ~/_ (_) www. uazu.net (_) ____ /=\ ____ ~/_ ____ (_) uazu.net
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