From: rjn@hpfcso.FC.HP.COM (Bob Niland)
Subject: LD#03: Intro to Surround Sound
Date: 14 Nov 91 18:06:38 GMT

re: #03 The soundtrack comes after you...                  Revised: 12 Nov 91

Surround sound is available from VHS/UHV/IRD broadcast TV, video tape, laser
video disc and a few audio CDs.  The topic is included in my LD article
series because surround is frequently the next enhancement sought after
obtaining an LD player.

There has been a fair amount of discussion over the years in rec.video,
rec.audio and rec.arts.movies on the subject of surround sound.  Much of it
has concentrated on theory; why recovery of 3 or 4 channels of sound from 2
channels of data is [im]possible, what artifacts are introduced, etc.

The objectives of this article are to address the questions:  
 - Why should you care about surround?
 - What is the "return on investment"? 
 - Is it worthwhile upgrade, or just a distracting acoustical gimmick that
   will quickly grow tiresome?
 - How important is it compared to other system upgrades?
 - What else do you need to know that the salesperson and literature won't
   tell you?


Some History:

Surround sound is not new.  Disney's "Fantasia" (1940) had discrete
6-channel sound, as did the Cinerama series of movies in the 50s.  Surround
sound in the home is not new either.  15 years ago it was called
"quadraphonic".  Indeed, the "Dolby Surround" system of today is not much
different from the CBS "SQ" matrix system of a decade ago.

"Dolby Stereo" = "Dolby Surround" = "Dolby MP", for home purposes.

Many of the "stereo" soundtracks on your laser video discs and VHS tapes
have long been encoded for surround.  This is because the encoding for
"Dolby Stereo" (Dolby Motion Picture matrix, or simply Dolby MP) is the same
as for home "Dolby Surround".  It is easier to simply transfer the encoded
signal from the theatrical audio master (or release print) to the video
master, than to decode to simple stereo or go back to the pre-encoded audio
elements and remix.

Unfortunately, most of the press coverage of surround has focused on
technical specifications, and none that I have seen attempts to give you any
idea of what surround actually *sounds* like.  Let me start with that...


The Experience of Surround:

  * It may be a very long time before we have convincing 3-D video, but
    effective 3-D audio is here today.  The audio portion of a surround
    presentation fills the entire listening space.

  * The difference between surround sound and conventional stereo can be as
    dramatic as the difference between stereo and mono.

  * To demonstrate this, during a sequence when the surround channel is
    active, try switching "effects OFF" on the processor.  The consequence
    is that the sound collapses to the front of the room.  Switch it on, and
    sound floods the room.

  * Observation:  you can notice the *difference*, but on a tastefully
    mastered surround program, you often don't consciously notice the
    presence.  The program is simply more involving.  The psychological
    distance between you and the program is reduced.  The image may still be
    at arm's length, but the sound joins you in the room.

  * Of course, on a tastelessly mastered work, herds of objects noisily
    zooming out into the room can become an irritation, but films like that
    are apt to be infested with myriad artistic defects of other kinds.

The surround effect is almost subtle.  Unless you have been informed that
you are listening to a surround-encoded program on a surround system, you
are likely to simply have a more engrossing viewing experience, without
necessarily knowing why.  You quickly get accustomed to hearing "rear"
sounds from behind, after all, in real life(TM) that's where they come from.

However, the general public is not clamoring for surround, 70mm, wide aspect
ratios or 60 frames/sec., because they are not consciously aware of the
contributions made by these technologies.  None, including surround, is
quite as profound and easily identifiable as the difference between, for
example, silent-vs-sound or B&W-vs-color.

Surround may not be getting the public attention it deserves, but then, the
lack of technology awareness is desirable in art.  You don't want the medium
to overshadow the message.

Putting Surround in Perspective:

It is possible to create a home surround theatre whose sound exceeds that of
your local 35mm "Dolby Stereo" movie hall.  You will not be able to exactly
duplicate the directionality of a 70mm Dolby hall, but at least the audio
fidelity of the home laserdisc setup can equal or exceed that of 6-channel
magsound film.

However, surround sound is NOT the first step in a home theatre.  If you are
watching VHS tapes on a 13-inch dime-store TV and listening to the audio
through the TV, or even the 5-inch speakers of a $100 discount store "rack"
system, then begin your upgrade elsewhere.  Don't get surround until you
have high quality in the following other areas...

 * Signal source: The absolute minimum for tape is VHS linear (analog)
		  stereo.  VHS linear mono is incapable of surround, and you
		  may not be satisfied with linear stereo.

		  I suggest a LaserDisc player, Satellite IRD, quality
		  stereo from cableTV or reliable local stereo VHF/UHF
		  broadcast.  Since there is not much surround broadcasting,
		  and quality cableTV is so rare, making the jump to laser
		  lightspeed will do more for your viewing pleasure than
		  adding surround to an analog VHS setup.  If LD is
		  inappropriate for you, then a VHS HiFi deck is indicated.

 * Monitor:       I suggest at least a 23-inch display (whether direct-view,
		  front- or rear-projected) with at least 350 lines of real
		  horizontal resolution, composite video input, and capable
		  of correct setup for geometry, size (overscan), black
		  level, white level and chroma.  View at distances of
		  between 4 and 8 picture heights.

 * Audio:         The main (front) channels need to have speakers with
		  fairly flat on- and off-axis response, with no resonances,
		  no breakup or distortion at moderately loud listening
		  levels, and backed by an amplifier of adequate power that
		  adds no problems of its own.  The treble response needs to
		  be flat to 7KHz or more, and the bass response needs to
		  reach down to at least 100Hz - the lower the better, since
		  film/video programming has much more deep bass than music.

		  If, for example, you can't tell the difference between CD
		  and pre-recorded audio cassettes on your system, you
		  probably need a complete audio upgrade.

Note on MTS:  VHF/UHV broadcasts encoded for NTSC-MTS stereo can carry
surround, but the stereo signal is often trashed by the local broadcaster or
cable operator, leaving you with a mono, [re]simulated stereo or highly
distorted stereo signal.  Don't get surround just for MTS programs unless
you are certain that you have reliable access to solid stereo programming,
and you have decent MTS decoder in your TV (many MTS decoders are junk, even
in "hi end" sets).

Note on Mono:  If you play a surround-encoded signal on a mono VCR or TV, or
through a mono audio system, mixing the left & right together, any sound
intended for the "surround" channel will be cancelled out altogether and
will be inaudible.  For this reason, some stereo surround material is
labelled "non-mono compatible".  In fact the surround channel component of
ALL surround program material is non-mono-compatible.


Some surround titles:

If you get an opportunity to demo surround, make sure you are using source
material that is worthy of the system.  Be advised that:

  a. Many video sources with surround sound aren't so identified on the
     media jacket.  Sometimes your ears or the "Dolby Stereo in Selected
     Theatres" that appears in the trailing credits are your only clues.

  b. Conversely, the appearance of "Dolby" in the trailing credits is no
     guarantee that a Dolby-ized stereo master was used for the video
     release (although it is rare that this is not the case).

  c. Even if "Dolby" or "surround" appears on the jacket, the effect may
     be less than dramatic, and may be largely ambience and echo.

The following laser video disc (LD), from the IMAX movie, is what I use for
surround demos:

The Dream is Alive {CAV}              (Ferguson, 1985) Lumivision  LVD9019

The following two laser disc titles also have very effective surround
programs.  I cannot vouch for the non-Criterion pressings of "Ghostbusters".
I also cannot tell you anything about tape editions.

Empire of the Sun {CAV}              (Spielberg, 1988) WB         11844
Empire of the Sun {CLV}              (Spielberg, 1988) WB         W11573
  (P-51 attack scene)
Ghostbusters {CAV}                     (Reitman, 1984) Criterion  CC1181L
Ghostbusters {CLV}                     (Reitman, 1984) Criterion  CC1182L
  ("Slimer" scene in hotel)

There are several test discs available for calibrating systems (and
verifying that your dealer's demo system is correctly set up).  The most
easily available is:

A Video Standard                          (Kane, 1989) RR         LD-101

The following LDs also have surround programs.  Although they are somewhat
less dramatic than those above, they are more pronounced than several other
"surround" discs I have examined.

Ben-Hur {the current letterbox edition}  (Wyler, 1959) MGM        ML101525
Die Hard                             (McTiernan, 1988) CBS/Fox    1666-80
Dragonslayer                           (Robbins, 1981) Bandai     LA098L14046
Dragonslayer {Cropped}                 (Robbins, 1981) Paramount  LV1367
LadyHawke                               (Donner, 1985) WB         11464LV
Ruthless People                (Abrahams,Zucker, 1986) Touchstone 485AS
Star Trek III - The Search for Spock     (Nimoy, 1984) Paramount  LV1621
Star Trek III - The Search for Spock[WS] (Nimoy, 1984) Paramount  LV12954
Star Wars                                (Lucas, 1977) CBS/Fox    1130-85*
The Witches of Eastwick                 (Miller, 1987) WB         11741A/B

One title to avoid:
Dolby Technologies: How They Work                      Pioneer    05458
Although a useful tutorial, it contains NO demo material.

Many of the articles referenced below also list demo titles.

* This is the new letterbox CLV edition with digital sound.  1130-80 (CLV)
  and 1130-84 (CAV) are cropped, although probably still surround.
 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

How does surround work?

[Over]simply stated, sound intended for the "surround" channel is recorded
in the normal left & right stereo channels, but out of phase with respect to
each other.  Anti-phase is "rear" (surround).  In-phase balanced in both
left and right is "center" or "dialog".  Other sounds are left, right or
some blend.

Some hall-dependent delay may be added (by the playback processor) to the
signal sent to the surround channel so that listeners far back in the
theatre won't hear the surround signal (esp. simulated echo) prior to the
original front channel sound.  In the Dolby system, the surround channel
also employs mild (5 dB) Dolby B noise reduction.

Depending on the decoder, other signal processing and channel amplitude
manipulation (steering) may be applied to attempt to cancel various signals
out of channels where they aren't "supposed" to be.  Normally the effect is
subtle and effective.  To hear the steering in action (and struggling), play
a dual-audio program, such as a laserdisc with a monophonic soundtrack on
analog channel 1/L and a commentary on 2/R.  With Pro Logic, the sound will
jump all over the place.  (Of course, a really smart unit may just give up
in the face of such mistreatment, and shut down decoding.)

If you listen to an un-decoded surround program on an ordinary stereo setup,
you may detect the out-of-phaseness of surround signals (particularly on
headphones - see postscipt).  The soundstage may appear to be wider than
your speakers, or you may actually have a psycho-acoustic experience of
sound from behind you (I noticed this on the "LadyHawke" LD, prior to having
a surround processor.)

Technically stated, the "Dolby Stereo" MP Matrix ENCODING looks like:

 Source Sounds                                                    As Encoded
                                                                       Lt
  Left ----> + -------------------------------------------------+---> Left
 Source      ^                                                  ^     Total  
             |                                         5 dB     |
             |                              100-7K     Dolby  +90 deg
  Ctr ---> -3 dB     Surround ---> -3dB ---> band ---> B NR --->|
 Source      |       Source                  pass      Encode -90 deg
             |                                                  |
             v                                                  v      Rt
  Right ---> + -------------------------------------------------+---> Right
 Source                                                               Total  

Pre-recorded "surround" programs have Lt and Rt in the left and right stereo
channels.  To extract the left/center/right/surround, you need a DECODER.

A primitive decoder merely passes Lt to left, Rt to right, then isolates and
subtracts the Lt and Rt, sending the Lt-Rt result to the surround speakers.
Yes, you can simply wire the surround speakers and a potentiometer across
the (+) terminals of the left and right front speakers.  Don't expect
wonderful results.  If you want to try this, see the June 1991 issue of
Audio magazine for tips.

A branded "Dolby Surround" decoder sends Lt-Rt thru a delay line (typically
20 mSec), then thru a 7 KHz low-pass filter (to keep natural and azimuth
error caused left/right source phase noise from being heard as surround) and
a 5 db (vs 10 on audio cassette) Dolby B-type noise reduction decoder.  A
master volume control and input balance controls are also provided.  Lt and
Rt may also be isolated, summed (Lt+Rt) and sent to the Center output.  In
any case, a maximum of 3 dB of separation is achieved between each adjacent
pair of:  left-center-right-surround-left.

A "Dolby Surround:  Pro Logic" decoder replaces the simple Lt-Rt (surround)
and Lt+Rt (center) extractions with an active adaptive matrix decode step.
For signals intended for one output, this circuit attempts to cancel them in
the others.  It also analyses the soundfield for signal dominance, and
focuses the sound toward those outputs.  The net result is that 30 dB of
separation is possible between any two channels.  Dolby Labs publishes a
"Principles of Operation" pamphlet that goes into more detail.

Incidentally, don't bother looking for any "Pro Logic" recordings.  Pro
Logic is used only in the playback processing.  The encoding (recording) of
Dolby Surround always uses the "Dolby Stereo" (aka "Dolby MP") matrix
described above.

Other moviesound and home surround terms:

"Ultra Stereo", "Chace Surround" and "matrix surround" are DolbyMP/Surround-
compatible anti-phase encoding schemes that do not bear the Dolby logo.  You
may encounter these terms on program material.  They will work on your Dolby
decoder.

"SRS" and "Q-sound" are not, as far as I know, Dolby-compatible.  They are
2-channel schemes that process the signal on playback (SRS) or prior to
recording (Q) and attempt to simulate 3-D sound placement with only the
normal two front stereo speakers.  The effect may be limited to a small
"sweet spot", and I don't recommend additional Dolby Surround processing.  I
have SRS on my Sony XBR TV, and with or without my external Pro Logic
decoder switched in, SRS-on is principally a "hum enhancer" and "listener
phase torture device".  SRS is no substitute for Dolby, as far as I'm
concerned.  Q-sound I have not heard extensively.

Dolby A, B, C, S and SR are noise reduction processes that have nothing to
do with surround except that Dolby Surround uses a modified Dolby-B on the
surround signal, and VHS linear stereo uses normal Dolby-B on both channels.
Dolby HX-Pro is a variable-bias technique for analog tape recording and has
nothing to do with playback, much less surround.

Dolby SR-D and Cinema Digital Sound (CDS) are digital sound encoding formats
for 35 and 70mm filmstock.  SR-D uses the vertical film area between the
sprocket holes.  CDS replaces the existing optical tracks.  Although 35mm
SR-D and CDS will motivate producers to create cleaner original sound
tracks, the LD digital sound format is already superior to both.

"THX" is a LucasFilm trademark for several things, two of which are related
to home surround:

 1. "THX Theatre" - THX is a certification process.  Theatres bearing the
    logo are periodically tested to ensure that they meet LucasFilm
    standards for audio environment and playback of surround-encoded film.

 2. "Re-recorded in a THX theatre" - THX logos on films and recordings
    indicate that the final mixdown was done with the recording console and
    engineer located in an actual THX-certified theatre.  This is intended
    to ensure that the film audio will playback in a consistent and
    predictable manner in all THX theatres.

 3. THX crossover - LucasFilm lists recommended audio components for THX
    theatres.  They also make a crossover, bearing the THX brand, which is
    only used in actual motion picture theatres.

 4. Home THX - LucasFilm has a testing and certification process for home
    audio equipment.  Those models which are submitted by the maker, and
    pass the tests, may exhibit the branding.  For example, in the Lexicon
    product line, only the CP-3 decoder is THX branded (probably due to the
    cost of re-submitting the CP-1 and CP-2).  THX branded equipment
    provides the promise of effective home theatre, but can still sound
    hideous if improperly set up and calibrated.  THX-branded equipment does
    NOT usually include dealer installation and adjustment.

 5. Surround channel de-correlation - Future THX-certified decoders are
    likely to be required to provide a small amount of digital pitch shift
    between the [two] surround speaker channels.  This is supposed to
    eliminate "imaging" and provide a more defocused surround sound.


The Equipment:

Here is what a largish Dolby surround setup looks like in the home.  You can
easily get by with only four speakers/channels (I do).


                        ============== Screen
            _             ....._.....              _
           | |            :   | |   :             | |
          /___\           :  /___\  :            /___\
        Left Front        :  Center :          Right Front
                          :.........:
                           Subwoofer
                               |
                               :
      __/|                     |                      |\__
     |__ |                     :                      | __|
        \|                     |                      |/
     Surround               Audience                 Surround
                               :
                               |
                               :
                  _____        |         _____
                  \   /        :         \   /
                   |_|         |          |_|
                 Surround      :       Surround


Room:  Any size room is acceptable if the decoder has adjustable rear delay.
    With fixed delay, you must get the surround speakers properly located
    with respect to the front speakers and the delay value.  See "surround"
    speakers below.

Center:  In both the theatre and the home, only a small portion of the
    audience is sitting near the centerline.  Those near the sides might
    hear front channel sound (sounds equal in both left & right speakers) as
    coming from the front speaker nearest their side.  If the processor has
    a "center" output, it attempts to isolate in-phase, balanced sound,
    usually dialog, which it thinks should be "front center".  It sends it
    to the center output and attempts to cancel it from the other outputs.
    That way, everyone hears "dialog" from the screen center speaker.

    Further, if you rely on the "center" sound to consist of an equal-and-
    in-phase signal emitted from both left/right front speakers, the sound
    waves will not arrive in-phase at all listening positions.  For example,
    a 6-inch difference in distances to L/R speakers results in a 180-degree
    group delay (and total cancellation of the direct wavefront) at 1000Hz.
    LucasFilm reports that center-channel dialog is easier to understand if
    it comes from a single speaker.  I am not yet using a center speaker,
    and can't contribute further comment.

Subwoofer:  Although film sound has much more bass energy than music, due to
    sound effects, the case for a subwoofer in a surround setup little
    different than for a normal stereo setup.  If your front speakers have
    wimpy bass, and you don't want to upgrade them, and you have lots of
    money, get a subwoofer (and maybe an amp to drive it).  If your system
    can reproduce cleanly down to 40Hz, you are probably OK as is.

    Pay attention to where the low-pass crossover is.  Having a filtered
    subwoofer output in the surround process *plus* a filter or crossover in
    the subwoof itself is not a "sound" idea.

Surround:  Notice that the side and rear speakers are *all* labelled
    "surround".  In a textbook Dolby theatre setup, there are a number of
    them and they all emit the same signal.  The point of having multiples
    is that each thus runs at a lower volume, the surround field is more
    uniform, and listeners near an individual surround speaker won't have
    their attention drawn to it.  Theatres use multiple surround speakers to
    achieve coverage.

    The LucasFilm-recommended number of home surround speakers is two,
    located to the SIDE, and not behind the audience.

    Dolby recommends that the surround speakers be located 5 feet closer to
    the average listener than the front speakers, and that the "surround"
    signal be electronically delayed by 20 milliseconds (for a net arrival
    delay of 15 mSec compared to "front" sound).  The Dolby publications "a
    listener's guide" and "Pro Logic Principles of Operation" both include
    distance-time nomographs.

Surround speakers:  You may be able to get by with modest surround speakers.
   In the Dolby mode of your decoder, the sound sent to these speakers is
   rolled off above 7 KHz, and although rolled off below 100 Hz during
   ENcode, it is NOT rolled off below 100 Hz during DEcode.  Any deep bass
   naturally out of phase in the original left and right sources will appear
   in in the surround channel (particularly if the processor has a subwoofer
   output).

   A case can be made for matching the speakers all around.  Several people
   have reported significant bass energy from their surround speakers, and
   some processors send full-range material to the surround speakers when in
   proprietary (non-Dolby) surround, ambience or venue simulation modes.

   A newly emerging LucasFilm/THX recommendation is that the home surround
   speakers NOT be pointed at the audience.  The new THX-certified speaker
   from Cambridge Soundworks, for example, has its bass cone pointed at the
   audience, but has two mid/high cones per unit, wired out of phase
   (dipole) and pointing sideways.  Furthermore, LucasFilm is suggesting
   that the sound sent to each of the surround speakers be slightly
   different ("de-correlated"), and they are leaning toward digital pitch
   shifting for this (not yet available in home surround processors, THX or
   other brands).

   You typically don't need a 14-inch woofer or thermonuclear tweeter for
   the surround speakers, or much amp power for that matter.  Any decent
   bookshelf speakers will do.  If I were looking for surround speakers
   today, I would seriously consider the Cambridge Soundworks "Ambiance"
   model, at ~$300/pair or the THX-certified model, "The Surround"
   ($400/pair).  Both feature an acoustic suspension mini with 6.5-inch
   woofer and 1-inch dome tweeter (2 tweeters in push-pull dipole on "The
   Surround").

   Any old amp that is well mated to the surround speakers will do.  I'm
   using a retired 55 W/ch receiver, driving a pair of Cambridge
   "Ensemble-I" units.

   Further note:  If the speakers and amps are not all identical, it will
   not be trivial to ensure that they are all in phase and balanced.  For
   phasing, I suggest testing one pair (each non-identical) in a simple
   stereo setup (with a mono signal), and correlating the polarity markings
   on the binding posts.  Be sure to use the eventual amp channels for this,
   as some amps invert the signal.


How to select a processor:

Step 1: Is your system ready for a decoder?

You may need (or want) a new main receiver or amplifier.  The surround
process requires exporting the raw stereo-matrix signal at the pre-amp
(line) level in the receiver/amp, then feeding the decoded front signals
back in at that point.  The input stages of the receiver/amp handle the
matrix signal; the main output stages handle only the decoded "front"
signal.
                      Receiver or Amp
 __________          _________________
| Surround |---Lt---|  Pre  :: Power  |---L---|Spkr<
| Source   |        |       ::        |
| e.g. LD  |---Rt---|       ::        |---R---|Spkr<
| VCR,CD   |        |  Ext Proc Loop  |
`----------'        `--Out------In----'
                       |  |    ^  ^
                       v  v    |  |
                    .------------------.   .------.
                    |   In   Front-Out |-->| Rear |---|Spkr<
                    | Surround Decoder |   |      |
                    | Center   SubWoof |-->| Amp  |---|Spkr<
                    |  Out       Out   |   `------' 
                    `------------------'
                        |         |
                        v         v
                     .-----.   .-----.
            >Spkr|---| Amp |   | Amp |---|Spkr<
                     `-----'   `-----'
                     Dialog    SubWoof

If you do not have "external processor" capability, but have a separate
"record in" selector switch, you'll need to:
 - route the Surround Source into the "LD" or "VCR" input as usual,
 - set "record source" to select that input,
 - route the record-out jacks to the decoder,
 - route decoder front-out back into "AUX" or "TAPE2" or a similar unused
   line input, and
 - select "AUX" or "TAPE2" on the receiver/amp main selector switches.

Another work-around is to:
 - feed the surround source (if you only have one) directly into the decoder
   Lt and Rt inputs,
 - feed the decoder "front" line outputs into the main (stereo) receiver or
   amp (AUX or other line-level in), and
 - feed the "center" "surround", "subwoofer" outputs directly to the 
   secondary amps line-level inputs.


Step 2: Pick a Processor (or Receiver with integrated decoder).

As far as brands and models, I cannot help you very much.  My only exposure
to surround has been via the Lexicon CP-1, which has both certified Dolby
Pro Logic and a variety of other modes.  I can't really say whether or not
the lack of auto-azimuth, use of ordinary Dolby or simple matrix decoding
would be disappointing by comparison to Lexicon's all-digital Pro Logic.

I would look for the following features (prioritized):
 * Pro Logic (adds less than $100 to new receivers nowadays).
 * Master volume control.
 * Auto-balancing on input (for programs recorded out of balance).
 * Adjustable rear-channel delay.
 * All calibrations from front panel and/or remote control.
 * Auto-test-tone program for calibration (more below).
 * Non-volatile storage of adjustable parameters (below).
 * Effects defeat (below).
 * Auto-azimuth to remove group delay of source program channels out of
   phase or independently time-delayed (as when sharing a single DAC on LD).

When you demo, I suggest starting at the top so that you have a standard to
shoot for in a lower-priced decoder.  Have the salesperson run through the
setup proceedure, and listen to a surround test disc (like Reference
Recording's LD-101, "A Video Standard").  This will show you how much
trouble the process is (or isn't) and more importantly, will ensure correct
store setup.  Far too often, I have heard simple stereo setups in stores
that are out of phase.  I estimate the chances of a correct surround demo at
about 5%, rising perhaps to 50/50 at a "high end" store or "video salon".

If you are considering getting an integrated receiver/decoder, I suggest
getting ONLY a receiver with the Pro Logic brand, as it may otherwise be
difficult to upgrade to Pro Logic later.

There are some things to watch for, lest you end up with missing or
duplicate components in the system and/or high "hassle coefficient":

  * Tuning processor input gain, balancing the outputs, setting surround
    delay, etc.  are critical for acceptable performance.  Does the
    processor have easy step-by-step instructions?  Does it include a
    built-in pink noise generator for matching levels (or a separate
    tape/LP/CD with such a signal?); if not, consider getting a copy of the
    Reference Recordings LD-101 "A Video Standard" LD.

    Unfortunately, many calibration programs jump from channel to channel,
    never turning on pairs simultaneously.  It is very difficult to
    accurately set levels this way, particularly if you must leave the
    central seating position to make the adjustments.  I use a sound
    pressure level meter (Radio Shack 33-2050, about $40), parked at the
    listening center.  Since only comparative levels matter, you can also
    use a microphone feeding any metered recorder.  Adjust the record level
    (in PAUSE) to about 0dB, and set levels for all channels.  Incidentally,
    if using "phantom center channel mode" (no center/dialog amp/speaker),
    ignore the "center" test signal and just get left/right/surround
    balanced.

  * Does the processor or receiver supply its own surround channel amp(s)?
    If so, how many, and with what power?  Is the power adequate for the
    speakers selected?  Is the impedance matched to the number of speakers?

  * If a subwoofer output is provided, is it producing flat response, or
    does it incorporate a low-pass filter?  What does the subwoofer itself
    require?  Does the subwoofer include its own amp?  How seamless is the
    response overlap between the subwoofer(s) and the bass response of the
    front and dialog (if any) speakers?

  * If your main speakers are driven by an integrated amp or receiver, does
    it have an "external processor loop" that allows separation of the
    pre-amp and power amp?  If not, you may encounter complications in
    signal source selection and front/rear volume balancing.

  * Is there a single master volume control for all channels, controlled by
    the remote?  Having that control duplicated on the front panel of the
    processor is a plus; a servo-driven ganged potentiometer is ideal.  (The
    Lexicon CP-1 has *only* remote volume buttons, but does have "mute".)

  * Are "effects" defeatable, allowing simple front-only stereo/mono?  Can
    you bypass the processor altogether for critical ordinary stereo
    listening?

  * Does the processor have user-alterable presets for Dolby decoding,
    vendor-unique decoding, stereo ambiance enhancement and any other modes
    you will frequently use?  Are the settings non-volatile (preserved thru
    power-off)?


Finally, a feature to watch out for.  If the decoder does not bear the
double-D [)(] Dolby logo, find out why.  The missing logo indicates that the
vendor is unwilling to submit their design to Dolby for inspection, change
requests, re-submission, etc. leading to an official approval.  There are
reasons why this might be:

 1. They focused their design on low-cost and/or time-to-market, and were
    unwilling to pay the royalty for using the Dolby logo, and/or put up
    with the certification delay.

 2. They don't like the Dolby spec, and think they have a superior decoding
    scheme.  Of course, they could have done both their own and Dolby's.  If
    the decoder (alone) sells for more than about $500, this is probably the
    explanation.

 3. Their decoder is too primitive and/or low in quality to pass Dolby
    qualification.  It may also lack even simple processing, like surround
    channel delay.  If the processor is built-in to a receiver, monitor or
    other component, listen carefully.  If possible, A/B-it against a
    quality stand-alone decoder.


Step 3: Install, calibrate and enjoy your surround system.


Step 4: Use of a surround system for music.

If after reading all of the above, you suspect that there is an awful lot of
processing being done on the original stereo signal, you are correct.  Do
you want to have all that switched on when playing ordinary stereo music on
the same system?  I suggest "no", unless the music was specifically recorded
for surround (as a few CDs have been recently).

When playing music on my system, I switch from Pro Logic mode to "small hall
ambiance".  If your processor doesn't have any alternate modes, it is doubly
important that it have an "effects off" mode.  You may not like what Pro
Logic does to non-surround stereo music, particularly if you are critical
audiophile.
____________________________________________________________________________

References:

Available free from:  Dolby Laboratories
		      100 Potrero Avenue
		      San Francisco
		      CA   94103-4813
Write for: "Dolby Pro Logic Surround Decoder - Principles of Operation"
	   "Dolby Surround - a listener's guide"
	   "Heard Any Good Movies Lately?" (a list of Dolby Stereo films)
	   "Question about Dolby Surround"
	   "What is Dolby Surround"

Here are some recent magazine articles on surround and decoders.  The ones
marked (*) are by Bill Sommerwerck, who has been writing intelligently about
surround since before it was even "quad".

Surround sound overview                             Stereo Review    Apr 91
Home theatre sound overview                         Video            Mar 91
Surround sound buyer's guide                        Video Review     Oct 90
Surround sound overview                             Video Review     Sep 90
Surround sound overview                             BD Notebook      Dec 89
Surround sound overview                             Stereo Review    Nov 89
Surround sound overview                             Video Review     Sep 89

Surround Sound and THX                              Stereo Review    Nov 91
THX home theatre equipment summary                  Video            Nov 91
Recommended Components                              Stereophile      Oct 91
Home theatre sound survey                           Video Review     Sep 91
THX theatre sound system                            Audio            Sep 89
Surround sound survey                               Stereophile      Aug 89 *

Atlantic Technology Pattern system                  Stereo Review    Aug 91
AudioSource SS-Two Dolby Surround decoder           High Fidelity    Oct 88
dbx CX1 surround sound integrated amp               Stereophile      Sep 88  
Denon AVC-2000 integrated surround amp              Stereo Review    Sep 89
Fosgate 3608 surround sound decoder                 Perfect Vision  Fall 89
Fosgate DSL-2 Pro+ surround processor               Video            Apr 91
Fosgate DSM-3610 Surround Processor                 Audio            Mar 89
Hitachi HA-V5EX A/V amplifer                        Video Review     May 91
JVC AX-V1050V surround receiver                     Audio            Aug 91
JVC RX-801V surround receiver                       Stereo Review    Oct 89
JVC XP-A1010 digital acoustics processor            Audio            Sep 89
JVC XP-A1010 digital acoustics processor            High Fidelity    Jan 89
JVC XP-A1010 digital acoustics processor            Stereophile      Dec 89 *
Kenwood KA-V8500 A/V surround receiver              Video Review     Oct 91
Kenwood KR-V9010 surround receiver                  Stereo Review    Nov 89
Lexicon CP-1 surround sound decoder                 Stereophile      Jan 89 *
Lexicon CP-1 surround sound decoder                 Audio            Nov 89  
Lexicon CP-1 surround sound decoder                 Perfect Vision  Fall 89
Lexicon CP-1 surround sound decoder                 Video Review     Jan 90
Lexicon CP-2 surround sound decoder                 Stereophile      Dec 89
Lexicon CP-2 surround sound decoder                 Audio            Mar 91
Luxman F-114 surround sound processor/amp           Audio            Nov 91
NEC PLD-910 surround sound processor                High Fidelity    Oct 88
NEC PLD-910 surround sound processor                Stereophile      Aug 89 *
Optimus (Radio Shack) STAV-3200 A/V receiver        Video Review     Feb 91
Onkyo A-SV810PRO A/V integrated amplifier           Video            Jul 91
Onkyo A-SV810PRO A/V integrated amplifier           Video Review     Jul 91
Onkyo A-SV810PRO A/V integrated amplifier           Stereo Review    Aug 91
Onkyo TX-SV50PRO A/V surround receiver              Video            Nov 91
Onkyo TX-SV70PRO A/V surround receiver              Video Review     Nov 91
Pioneer AVX-4900S A/V surround receiver             Video            Nov 91
Pioneer SP-91D digital sound processor              Stereo Review    Dec 89
Pioneer SP-91D digital sound processor              Perfect Vision  Summ 90
Pioneer VSX-D1S A/V (surround) receiver             Video Review     Mar 91
Pioneer VSX-D1S A/V (surround) receiver             Stereo Review    Jan 91
Proton SD-1000 surround decoder                     Audio            Apr 91
Sansui AV-7000 a/v receiver                         Stereo Review    Nov 91
Sansui RZ-9500AV A/V receiver                       Stereo Review    Feb 91
Sansui RZ-9500AV A/V receiver                       Video            May 91
Shure HTS 5300 Home Theatre Sound (entire system)   High Fidelity    Jul 89
Shure HTS 5300 Home Theatre Sound (entire system)   Video Review     May 89
Shure HTS 5300 Home Theatre Sound surround decoder  Audio            Jul 89
Shure HTS 5300 Home Theatre Sound surround decoder  Stereophile      Aug 89 *
SSI System 4000 II surround processor               BD Notebook      Dec 89
SSI System 4000 II surround processor               Audio            Mar 91
Sony SDP-777ES digital surround processor           Audio            Aug 89
Sony TA-E1000ESD digital surround amplifier         Audio            Jun 91
Synergex ESP-7R surround sound decoder              Perfect Vision  Fall 89
Technics SA-GX505 A/V surround receiver             Video            Nov 91
Technics SA-GX505 A/V surround receiver             Stereo Review    Oct 91
Yamaha DSP-3000 surround sound processor            Stereophile      Sep 89 *
Yamaha DSP-A1000 digital surround amplifier         Audio            Jun 91
Yamaha DSP-A1000 digital surround amplifier         Stereo Review    Jul 91
Yamaha DSR-100 surround sound decoder               Stereophile      Aug 89 *
____________________________________________________________________________

Some related surround traffic from other contributors (>) & my replies.

> Whenever possible, I use headphones when watching a movie on laserdisc.
> I use a good pair of Sony headphones, the enclosed kind that kill any
> external sounds, model MDVR-6 or something like that.  Some movies are
> truly awesome this way.

> How does surround sound compare to headphones, in terms of the 
> listening experience?

I don't watch video with phones on, but for the purposes of answering this
query, I got out the MDR-V6's and gave it a try.

Generally:

  Normal stereo speakers:  Wall (or "stage") of sound in front of you.
  Stereophones:            Line of sound between your ears.
  Surround speakers:       Field of sound all around you.

The headphone experience is one of having all the audio happening inside
your head.  This is certainly "different" than stereo speakers.  Whether or
not it is "better" is a matter of taste and exposure.  On an ordinary stereo
program, once the brain has learned to associate the sounds with the visual
action, there's not much difference between phones and speakers.  

Stereo video soundtracks share the same problems that musical works (esp.
early stereo recordings) have when heard via phones.  If individual sounds
are fed into the mix (say, the left channel) without bleeding some reverb
(into the right), they sound artificial.  They sound pasted on, and not part
of the program.  In a speaker (or theatre) setup, this is not a problem,
because the room adds the necessary blending and ambiance.

On undecoded surround programs, however, I noticed two more things:
  1. The anti-phase encoding of surround information can be distracting.
  2. There is no sense of "front" and "back".

On (1):  An effect that is supposed to be a sound moving from front center
         to rear center is a sound that starts in-phase and shifts to
         anti-phase.  If you are sensitive to phase (as I am), it is
         slightly annoying.  The "location" of the sound shifts from head
         center to "both ears at once".  It does not move front-to-back.

On (2):  Given a stationary head and sound source, the way that the human
         auditory system determines "front" and "back" is through subtle
         amplitude, phase and group delay differences between the sound at
         each ear, plus frequency contouring, local reflections at each ear,
         and bone conduction.  The head and outer ear re-shape the sound
         spectrum, based on the direction of the source.  This is why, in
         real life(TM) or in a surround speaker setup, sounds from behind
         you are experienced as coming from behind you.

         Real life(TM) surround is therefore completely different than
         matrix/Dolby encoded surround.  The encoded signal is not at all
         naturally directional to the headphone listener.  Building
         headphones with 4 speaker assemblies doesn't help, either.  Vendors
         (even Stax) try this from time to time with little success.

It is possible to largely re-create a 3D listening experience for headphones
via a special sub-species of stereo known as "binaural" recording.  This
requires a two-track recording made using an anatomically correct human head
dummy, with microphones in the ear canals.  The resulting work preserves all
the directional cues imparted by the human anatomy.  Obviously, the work
must be heard via earphones (optimally, the intra-aural in-the-ear type, so
as not to add any further anatomical processing).

Some radio dramas (including Stephen King's "The Mist") have been recorded
binaurally.  Very few musical recordings are made this way, and to my
knowledge, NO video programs have binaural tracks.

The apparent bottom line:
  * For ordinary stereo programs, headphone listening is an acceptable
    alternative to speakers, perhaps even preferrable, depending on your
    tastes and listening environment constraints.
  * For surround programs, headphones are no substitute for speakers
    unless the program is binaurally recorded (and no video material is).

Bob Niland 

/-------------------------------------------------------------------------/

> I think these laserdisc titles also have at least some great surround
> utilization:

>       Back to the Future
>       E.T. - The Extra-Terrestrial
>       Poltergeist
>       Star Trek II - The Wrath of Kahn
>       Young Sherlock Holmes

> These titles at least have great overall sound and may have good surround
> too (I can't remember for sure about the surround part):

>       Predator
>       Robocop
>       Star Trek IV - The Voyage Home
>       Starman
>       2010:  The Year We Make Contact

   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

> The absolute *BEST* disc for surround sound is _For All Mankind_.  The
> launch of a Saturn 5 can't be matched, and stage separation ...  WOW!

[Note - A correspondent who was working at the Cape at the time reports that
although impressive, the "surround" sounds on this disc are completely
faked.  - rjn]

> A low cost way to get into surround sound is with the Radio Shack decoder.
> You can get it plus a pair of speakers (Minimus 7's?)  for about $200.  If
> you switch it to use all of it's amp power for the back channel speakers
> and use your hifi for the front, it works pretty well.  It only has a few
> watts of power (15 or so?).  My front channel is a pair of Altec-Lansing
> 15" Voice of the Theater speaker systems driven by a 130 watt per channel
> amp.

/-------------------------------------------------------------------------/

* For surround programs, headphones are no substitute for speakers.

>> Would one of those "quad" headphones work for this case?  (I remember
>> the four speaker headphones being sold at the peak of the quad fad.)

> I suspect it depends on how fussy you are.  I have a pair of Koss quad
> headphones from the old quad days.  My father was into that non-fad and I
> ended up with them, along with his old receiver.  The headphones did
> produce a kind of four channel effect, although not the same effect that
> was produced by the speakers.  In the same manner, I can decode surround
> sound with the QS matrix decoder in the receiver, but sounds tend to
> wander about the room and seperation is not as good as in the theaters.  I
> would guess that I have something nearly as good as the low end surround
> sound decoders, but not nearly as nice as the new pro logic decoders.

/-------------------------------------------------------------------------/


re: >>  * For surround programs, headphones are no substitute for speakers.

> Would one of those "quad" headphones work for this case?  (I remember
> the four speaker headphones being sold at the peak of the quad fad.)

Well, as I said in the quoted article:

>> Building headphones with 4 speaker assemblies doesn't help, either.
>> Vendors (even Stax) try this from time to time with little success.

Let me elaborate.  Keep in mind that this is just a "thought experiment".
I have no actual experience with 4-element headphones.

The directional cues that occur to me are:

  * Ear effects:  (the "pinna" is the external part of the ear)
                  directional response envelope
                  local reflections in the pinna
  * Head effects: (comparing one ear to the other)
                  diffraction of sound when one ear is masked.
                  arrival-time differences
                  response/amplitude differences
  * Body effects: feeling louder and/or lower frequency sounds on one side
  * Conduction:   A fair amount of mid- and low-frequency energy reaches
                  the inner ear via bone conduction.  Dummy microphone heads
                  are even being made with false skull bones for this reason.
  * Environment:  With "real" sounds, the location of the sound with respect
                  to the listening environment is stable as you move your
                  head.  Even when you are "still", your breathing alone is
                  moving your head enough to cause several degrees of phase
                  difference at voice frequencies, not to mention shifting
                  your position in any room standing wave patterns.

With 4-element phones, assuming that the "rear" elements are actually at the
rear of the housing, the only cues preserved (maybe) are the pinna effects.

The head, body, conduction and environment effects are totally lost, because
the sound from any single element is heard only in one ear, and the
relationship between ears and sources is constant.  I'm not even sure that
the pinna effects are detectable, given that the sound from any element is
bouncing around in the phone housing as well as off the ear.

I suspect that it is possible to detect a difference between 2-element and
4-element operation of quad-phones, but I'll bet a cup of HP coffee that
quad-phones provide a very unsatisfactory surround experience, beyond
allowing you to employ the decoder to remove the anti-phase and Dolby-B
encoding of the raw stereo signal.

Regards,                                              Hewlett-Packard
Bob Niland      Internet: rjn@FC.HP.COM               3404 East Harmony Road
                UUCP: [hplabs|hpfcse]!hpfcrjn!rjn     Ft Collins CO 80525-9599

.
