MOTM

The switching from the carrier to the NS is performed
on the HP channel only, correct?  Just want to make
sure I am not missing anything.

Is the 12 kHz cut-off based on designs you have seen
or is based on linguist analysis?  IOW, how arbitrary
is that point?

--Shemp

> One easy way to extract voiced/unvoiced information
> (as I recall) is 
> to use a high-pass filter with a cutoff at 12 kHz or
> so.  Plosive and 
> fricative sounds have more energy in the higher
> regions of the 
> spectrum, so when an S or F or P or whatever is
> spoken, the HP filter 
> passes the high spectra which is rectified and used
> to trip a Schmidt 
> trigger (threshold detector).  This is used to
> control an electronic 
> switch, which switches from the default carrier to a
> noise source.  
> As soon as the unvoiced sound is over, the switch
> reverts back.


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