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From: caf@cdi.UUCP
Newsgroups: net.audio
Subject: Which audio gadgets work (for me)
Message-ID: <204@cdi.UUCP>
Date: Sat, 11-Jun-83 00:05:32 EDT
Article-I.D.: cdi.204
Posted: Sat Jun 11 00:05:32 1983
Date-Received: Tue, 7-Jun-83 18:02:57 EDT
Lines: 122

The recent articles about equalizers has tempted me to post
my 2 cents' worth about various audio gadgets.

EQUALIZER:  Get (borrow?) a unit with a spectrum display and microphone.  Use the
microphone and the noise source to equalize your system by moving the
speakers, not by equalizing the audio.  If you can't get the response
reasonably flat by moving the speakers around, you should have spent
the money on better speakers or a different room.  The usefulness of an
equalizer is "directly" proportional to the variability of your audio
sources.  Most (not all!) movies and concerts on videodisc are
especially amenable to improvement, if only because some engineer has
munged the sound with HIS equalizer.  Recent, HIGH QUALITY "mainstream"
audio recordings rarely need correction with an equalizer.  Your
equalizer should be located where you can hear the speakers fairly
well.  For greatest enjoyment, the RTA display should be visible from
the listening position.  Read the article in June 83 High Fidelity.

SONIC HOLOGRAPHY:  In many of Carver's products, the invention lies as
much in the sophisticated name as in the actual circuit itself.  I have
found the holography effect to be convincing on but a small number of
records, primarily small groups.  Placement of speakers is critical for
sonic holography.  Proper (for holography) speaker placement may by
itself improve the stereo imaging sufficiently to make the exercise
worthwhile.  Sometimes recordings sound muddy with the holography
switched in.  Be sure to read the article on holography in the May 83
Audio.  Unfortunately, proper speaker placement (for best imaging) may render
the room useless for other activities.

AUTOCORRELATION NOISE REDUCTION:  The word correlation had me confused
about how this circuit works; I had been thinking of multipliers in
signal detection.  Actually, autocorrelation is merely an evolution of
the 1950's Scott Dynaural noise filter.  To my ears, autocorrelation does
NOT reduce hiss without affecting instrumental timbers as the
advertising suggests.  I find the noise reduction that results from a
slight (1.15 or 1.2 to 1 linear expansion) to be somewhat more musical
in most cases.  Sometimes, (with particularly noisy sources) autocorrelation in auto threshold
mode is useful in conjunction with expansion to reduce swishing.  The
low frequency correlation filtering is ofen effective in cleaning up
record rumble without undue side effects.  On the Carver preamp, the
"correlation threshold" can be set so that only the low frequency
filtering is effective.

LINEAR EXPANSION:  On many program sources, a linear expansion of from
1.1 to 1.3 to 1 will simultaneuosly reduce background noise and
add/restore emotional "punch" to the program.  Sometimes I can use
expansion and equalization to make a 10 year old record sound almost
as good as a CD. (Well, good enough to put off buying the CD until
prices come down ...)  I use a DBX 128 which was on sale at $200 off
(discontinued model?) an am quite happy with it.

DBX RECORDS:  To my ears, DBX records are almost as musical as CD's on
most material.  The main problem is limited selection.

CX NOISE REDUCTION:  CX encoding was CBS's "answer" to DBX.  CX
sacrifices some of the awesome noise reduction potental and relative
freedom from side effects that characterize DBX for a measure of
compatibility with undecoded playback.  There are two distinctly
different CX systems.  The original used compansion mainly controlled
by frequencies above 500 Hz., and this version is used on Laser
videodiscs.  For records (and, I think, CED discs) this cutoff
frequency was changed to 100 Hz, resulting in stronger compansion at
the expense of audible swishing accompanying low frequency sounds.
Although this cutoff frequency is even lower with DBX, swishing is
usually inaudible because the greater compansion keeps signal levels
well above record hiss.  To date, there has been bloody little
classical music (the only kind I really care about) on CX'ed records.
Fortunately, it is easy to modify early CX disc decoders for use with
old laser viseodisc players.  A recent Billboard article casts doubt on
the future of CX records.

STEREO DOLBY VHS:  At the two hour speed, the JVC 2650 gives passable
frequency response and s/n ratio for much material.  Just don't try to
record a harpsichord recital.  The dynamic range can be improved by
using DBX tape encoding in place of the Dolby B that is built in to the
2650.  Chrome tapes seem to sound better with DBX because of less
modulation noise (asperity).  Most tapes have unberable drouputs except
for T-160's, but this may be a problem with my particular VCR.  Since
the 2650 has no manual record level controls, I use an old preamp to
set the recording level.  Before spending money for a stereo VCR, I suggest you
listen carefully to the sound quality of simulcasts available in your
area.  Beta HI-FI or the VHS equivalent (if it ever appears) would be an
improvement because of the improved sound at the > 2 hour speeds
(assuming you have something to record that justifies the better
sound).

GROUND LOOPS:  Ground loops are more troublesome in combined
audio-visual setups.  Amplifiers with SCR power supplies (such as the
Carver M400) exacerbate the situation.  Look for video gear with pseudo
differential video inputs (shield not connected directly to chassis)
for help.

LASER VIDEODISC PLAYER:  The sound quality of Laserdiscs has been
improving to the point that the best (with possibly some help from DBX
and/or an equalizer) sound nearly as good as any record, almost as good
as DBX or CD.  Unfortunately, the mechanical noise from the player can
be a nusiance.  The original Pioneer player is not so great at driving
long, high capacity audio cables.

PROJECTION TV:  The large screen of a projection TV will affect room
acoustics to some degree, especially stereo imaging or holography
effect.  The best location (sonically) for the speakers may be a few
feet behind and to the sides of the screen.

DOLBY STEREO:  The background channel in Dolby Stereo encoded movies
may be recovered with a speaker or pair of speakers driven by the
sifference signal between the left and right channels.  I have not
heard a true Dolby Stereo decoder yet; I would appreciate comments
about how this compares with the Hafler type connection.

SYNERGISM:  Although a LaserDisc feeding a Kloss projection TV is no
visual match for 70 millimeter film, a fine home audio system can
easily provide sound better than that heard in almost all theatres.
The home setup is effective for programs with a strong emphasis on
sound, such as operas and movies with great music and/or sound
effects.

Chuck Forsberg cdi!caf
-- 

	Chuck Forsberg, Chief Engr, Computer Development Inc.
	6700 S. W. 105th, Beaverton OR 97005   (503) 646-1599
	cdi!caf