[sdiy] 440Hz Reference Oscillator.

[Magnus Danielson]

From: Ian Fritz <ijfritz at earthlink.net>
Subject: Re: [sdiy] 440Hz Reference Oscillator.
Date: Tue, 06 Jun 2006 15:33:03 -0600
Message-ID: <6.2.1.2.2.20060606153008.02c1ffa8 at mail.earthlink.net>

Ian,

> The "A" you get from the telephone co is accurate.  You could probably run 
> it through a filter to get a sine.

Ehm... only if they actually "play" A. Not all do you know. ;O)

Infact, chances are that they not necessarilly have a musical note frequency.

Just look in ETSI EN 300 001 (go ahead and download it if you like, you need to
get the password, but it's free) and be amazed over the variation, and I am
sure that things have shifted away from that one. Sigh.

Whatever frequency synthesis they do, it may be any form of approximation
(consider the ration 8000 / 440 which becomes 18.181818... samples/wawe).
What you can count on is the stability, which should be sufficient for musical
applications, even with them new VoIP phones you should at least have a lousy
+/- 100 ppm crystal.

So, not without proper verification. Hmm. I haven't done that test yeat!

Telephone is a degrading service... sigh!

Cheers,
Magnus