In article 4a53c6a2.2006077968@localhost, Don Pearce
wrote:
On Mon, 06 Jul 2009 10:39:03 +0100, JohnT wrote:


Thanks for the comments. What I am trying to do is to optimise a voice
signal in the presence of high background noise levels, so I need a
fairly sharp bandpass filter. I have of course tried simple RC sections
for HPF and LPF but this is not sufficiently sharp for the purpose.


The just make a multiple pole filter using op-amps. There are plenty of
cook book style recipes to do this. The usual way to maximise speech
intelligibility would be, as you say, a pass band of 300Hz to 3kHz
(approx), but between those extremes, you should have a 6dB per octave
rise to accentuate the top end.

That is so. I use cookbooks for such purposes. FWIW I've put some of the
simpler design rules on the web at

http://www.st-andrews.ac.uk/~www_pa/...rt3/page2.html

The snag is that we still don't know the signal levels, impedances, etc,
that would suit John's requirements.

Slainte,

Jim

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