Newsgroups: comp.speech
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From: tjrob@iexist.att.com (Tom Roberts)
Subject: Re: Recording telephone speech input
Message-ID: <D80DMp.80o@ssbunews.ih.att.com>
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Organization: AT&T Bell Laboratories
References: <3o6lb2$iuo@netaxs.com>
Date: Wed, 3 May 1995 15:28:01 GMT
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In article iuo@netaxs.com, nickm@netaxs.com (nickm) writes:
> [...]
>The Rhetorex cards are capable of recording linear 16-bit samples
>at 8KHz  bit PCM. The best the Dialogic cards can do is 8KHz mu-law PCM 
>(a companding algorithm which writes the data as 8-bit samples).
> [...]

Don't knock Mu-Law recording. In most parts of the U.S.A., your telephone call
will have been transported as Mu-Law PCM for at least part of its trip, if not
most of it. For example, if your call traverses either AT&T, MCI, or Sprint,
the odds are >99% that Mu-Law conversions will have been applied. I don't
know about the local carriers, but in most cities the vast majority of calls
will traverse some Mu-Law system as well.

Once Mu-Law conversions have been applied, recording with higher quality (e.g.
16-bit linear) will not give better quality recording. Note, however, that
multiple Mu-Law conversions should be avoided, if at all possible. This
means you really want a digital phone line (ISDN or direct T1/E1) connected
to a digital interface on your recording system.

Tom Roberts	tjrob@iexist.att.com
AT&T Bell Laboratories
