[CM] telephone noise spectrum

[Robert Komar]

On Mon, 9 Feb 2004, Bill Schottstaedt wrote:

> I was goofing around lately trying to clean up a
> recorded telephone conversation (see sndscm.html,
> the last section), and was wondering if anyone
> knows the source/characteristics of the loud
> background tone -- it's not 60 cycle hum harmonics
> as far as I can tell; sounds like a high-voltage
> tranformer.  I tried to notch it out, but I'm
> not really having great success so far.
>
> I tried to check the net, and wasted a lot of time...

I was cleaning out my Inbox and came across a message I wanted to
respond to when it first came out...

Have you figured out what the frequency is?  I was wondering if
it was just a quiet version of the dial tone, which is a 440 Hz
signal.  I didn't make the suggestion right away because I thought
that you would have tried notching that right away, it being
fairly common knowledge that you can use the dial tone to tune
a guitar.

Rob Komar