Path: utzoo!attcan!uunet!nancy!wsrcc!wolfgang
From: wolfgang@wsrcc.uucp (Wolfgang S. Rupprecht)
Newsgroups: sci.electronics
Subject: Re: ..but what about _output_ filtering for D/A's?
Message-ID: <1990Oct20.180310.6506@wsrcc.uucp>
Date: 20 Oct 90 18:03:10 GMT
References: <1319@beguine.UUCP>
Organization: Wolfgang S Rupprecht Computer Consulting, Washington DC.
Lines: 22

>And  I've always wondered: can two ultrasonic sounds or an ultrasonic
>and audible sound beat to create an audible tone?

An some people have pointed out, the whole trick to getting the beats
is a non-linear addition of the two sine waves.

The ear is fairly linear in that respect.  You won't hear the beats.

Electronics on the other hand are hard pressed to be called linear.
You will definitely get sum and difference products.

This is actually the basis for some bug-foilers.  Just activate
several powerful ultrasonic sources.  Human ears won't hear the
beats, but the electronics sure will!  

It usually best to have totally separate oscillators for this, since
you don't want the sinusoids mixing in your electronics.

-wolfgang
-- 
Wolfgang Rupprecht    uunet!{nancy,usaos,media!ka3ovk}!wsrcc!wolfgang
Snail Mail Address:   Box 6524, Alexandria, VA 22306-0524