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From: ark@alice.UucP (Andrew Koenig)
Newsgroups: net.med,net.info-terms,net.audio
Subject: Re: "Ultrasonic" hearing
Message-ID: <4778@alice.UUCP>
Date: Tue, 7-Jan-86 11:47:04 EST
Article-I.D.: alice.4778
Posted: Tue Jan  7 11:47:04 1986
Date-Received: Wed, 8-Jan-86 08:35:43 EST
References: <590@harvard.UUCP>
Organization: Bell Labs, Murray Hill
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Xref: watmath net.med:3066 net.info-terms:783 net.audio:7022

> I don't know anything about so-called "Ultrasonic" hearing, but
> I do know that the flyback transformers on most monitors emit a
> buzz around 17-19 khz; the exact frequency escapes me right now.  
> This is "ultrasonic" only for most people over 30 or 35 years of age.

I think it's 15,750 Hz: 525 lines on the screen times 60 Hz refresh rate,
divided by 2 because of alternate scanning.  People's ability to hear
it seem to vary greatly by individual, even among children.