[Asterisk-Users] Woodpeckers

[Steve Underwood]

Greg Hill wrote:

>My first thought was an RC filter, too. But I'd suggest that 500 Hz is too
>high a cutoff, because a note like a middle C is 256 Hz. I don't think
>it's uncommon for a voice (especially a male voice) to be in that range
>frequently. Although (in English, at least) vowels generally have a low
>frequency and sharp consonants (like a t) have a high frequency. It's the
>consonants which do the most for understanding a word, so maybe having
>those low frequencies attenuated wouldn't be so bad after all.
>  
>
The telephony codecs all filter hard below 300Hz and above 3400Hz, so 
your middle C gets attenuated quite a lot on any normal phone line. The 
F0 (basic pitch contour) of my voice can go below 50Hz. However, 
filtering at 300Hz clearly doesn't screw that up, since all phones do 
that and voices still sound OK :-) The 3400Hz limit has more effect on 
voices, especially a trill woman's voice. 7kHz telephony makes 's', 'f' 
and other unvoiced sounds much easier to distinguish. That has 
suprisingly little effect on overall intelligibility, though.

Regards,
Steve