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From: sjc@angband.UUCP (Steve Correll)
Newsgroups: net.audio
Subject: Re: equalizers
Message-ID: <71@angband.UUCP>
Date: Fri, 26-Jul-85 14:46:51 EDT
Article-I.D.: angband.71
Posted: Fri Jul 26 14:46:51 1985
Date-Received: Sun, 28-Jul-85 06:27:21 EDT
References: <7351@watdaisy.UUCP>
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Organization: S-1 Project, LLNL
Lines: 48

> It is my impression that almost all differences between reasonable
> quality stereo components can be attributed to differences in
> frequency response across the audio spectrum.  Therefore, I have 
> decided that I should buy a multi-band equalizer.

> Second, I don't see how one could possibly calibrate the system by
> ear.  It seems to me that one would want to measure the SPL generated
> by a known source.  The source is (relatively) easy to come by; one
> can buy or build a tone generator.  Once upon a time, I saw a test
> record with a number of tones on it as well.  One can also build a
> SPL meter with a microphone and a volt meter, but that would measure
> the frequency response of the microphone more than anything else.
> Do there exist such meters at reasonable price?  If so, where can they
> be obtained?  Alternatively,  if I had a known source, I could 
> calibrate my own.

Equalizers are controversial because they introduce phase shifts and
small anomalies in the process of correcting for big ones, but I'll
avoid taking a position on that topic. You're right that calibration by
ear is dicey. Radio Shack used to sell a sound pressure level meter,
but I can't find it in the latest catalog; you might ask your local
store manager if it's still available. Supposedly pink noise is a
better source than pure tones, since the latter may excite narrow-band
room resonances and bias the results.  You can build a pink noise
generator plus multi-band equalizer for yourself from plans in the
National Semiconductor Audio-Radio Handbook, about $10 (for information
on buying it, call National at 408 737-5000).

Stereo Review used to sell for less than $10 an audio test record called the
SRT 14-A with a number useful signals, including 29 narrow bands of pink
noise spanning the audio spectrum. I haven't seen an ad for it lately, but
you might contact them for information:

   Stereo Review
   One Park Avenue
   New York, NY 10016
   (212) 503-4000

CBS labs also makes a number of test records, including "STR140: RIAA Pink
Noise Acoustical Test Record", which used to be available (again, I haven't
seen an ad lately) for $15 from:

   Old Colony Sound Lab
   PO Box 243
   Peterborough, NH 03458
-- 
                                                           --Steve Correll
sjc@s1-b.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc