Date: Thu, 21 Dec 2006 23:14:37 -0500 (EST)
From: "Keith F. Lynch" <kfl at KeithLynch.net>
To: WSFA members <WSFAlist at KeithLynch.net>
Subject: [WSFA] Re: Modems, and O.J. Simpson
Reply-To: WSFA members <WSFAlist at KeithLynch.net>

Ron Kean wrote:
> Keith F. Lynch wrote:
>> ... Just don't try to store modem signals as MP3s.  That trick
>> never works.

> To contrive a counterexample, I would think that 128 kbps MP3 mono
> could successfully replicate a Bell 103 (0-300 bps async FSK) signal,
> given the more than two orders of magnitude data rate overhead.

Just because there's enough room for an elephant in your living room
doesn't mean there's one there, or even that one would fit through
the door.

MP3 and competing standards are designed to compress sounds by
discarding subtleties that human ears don't notice.  Given that there
are no proven cases of anyone being able to read arbitrary 300 bps
modem signals by ear, I suspect those signals may exceed human
physiological limits, in which case MP3 and competing standards may
not capture enough information to uniquely reconstruct the signal.

I have heard of people who can read 75 bps modem signals by ear, so
presumably if you crank down the speed enough, it would work.  But why
bother?  That's not what MP3 is for.  There's a much, much better way
to compress audio if it happens to consist of modem signals:  Turn it
back into the bits the modem was conveying.

Either way, it should be simple enough to test.

> 8 MB for three hours works out to 5926 bps, so that is an
> impressively low encoded rate, considering that the slowest mono MP3
> rate for speech I have ever seen in use was 16 kbps.  And one does
> perceive a sound quality degradation at 16 kbps MP3 relative to,
> say, 128 kbps MP3.  At 5926 kbps, 375 hours of speech would fit on a
> 1 GB memory module.  I think that might be enough for one O.J. trial.

Bite your tongue!  Immensely long audio files where I can understand
what is being said only if I listen several times to each phrase while
concentrating really hard, having to get up and walk around every few
minutes to clear my head, is not my idea of fun.

At the moment I'm listening to some Bing Crosby Christmas music that
recorded maybe 70 years ago.  Its quality is incomparably better than
that DSS file.

The MP3 I had to work with today was much clearer.  At one point I
could clearly make out the lawyer whispering to his client, "watch me
make shit out of shinola."  I obviously wasn't meant to hear that.