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Subject: Ambisonic Surround Sound FAQ, v2.7
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Summary: Frequently Asked Questions by domestic listeners about
         Ambisonic Surround Sound.  Includes theory, practice, details
         of current decoder manufacturers and a discography of UHJ
         encoded LPs and CDs.
Keywords: Ambisonics, Ambisonic, surround sound, FAQ, UHJ
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Archive-name: AudioFAQ/AmbisonicFAQ
Posting-Frequency: monthly
URL: http://www.omg.unb.ca/~mleese/faq_latest.html
Version: 2.7
Last-modified: 11 August 1996

Ambisonic Surround Sound FAQ
****************************

Copyright ⌐ 1994, 1995, 1996 by Martin J Leese
Distribution is unlimited



Frequently Asked Questions by domestic listeners about Ambisonic
Surround Sound. Includes theory, practice, details of current
decoder manufacturers and a discography of UHJ encoded LPs and CDs.



0. Contents
===========

1. Where can I get this FAQ?
2. Corrections to the FAQ
3. What is surround sound?
4. What is Ambisonic Surround Sound?
5. What are W, X, Y and Z?
6. How does Ambisonics differ from quadraphonics?
7. How does Ambisonic Surround Sound differ from the Dolby surround
systems?
8. What were Matrix H and HJ?
9. What is UHJ?
10. What are BHJ, SHJ, THJ and PHJ?
11. Are UHJ encoded CDs available? *
12. What happens with stereo sources (conventional LPs, CDs, etc)?
13. Can Ambisonics decode Dolby MP?
14. Can Ambisonics decode Dolby Surround AC-3?
15. Can Ambisonics make use of Music DVDs?
16. Have Ambisonic decoders been manufactured commercially?
17. Are Ambisonic decoders being manufactured commercially?
18. If Ambisonics is so wonderful, why is it not a commercial success?
19. How many speakers does Ambisonics use?
20. From where can I obtain more information?
21. What about recording and studio processing? **
22. References
23. Acknowledgements
24. Trademarks
25. Obituary **

* Significantly changed from the previous version
** New in this version



1. Where can I get this FAQ?
============================

On the WWW at the following locations:

 o http://www.omg.unb.ca/~mleese/
 o http://www.york.ac.uk/inst/mustech/3d_audio/ambison.htm
 o http://darkwing.uoregon.edu/~jrusby/

By anonymous FTP from ftp.omg.unb.ca (131.202.34.4) in the directory
/pub/ambisonic (ie, from file://ftp.omg.unb.ca/pub/ambisonic/). The
file is called faq_v2_7.html or something similar, and is suitable
for viewing with Mosaic and other WWW browsers. PostScript and text
files derived from this HTML source file can be found in the same
directory.

It is posted monthly to the Usenet newsgroups rec.audio.tech,
rec.audio.pro, rec.audio.misc, rec.audio.opinion, rec.answers and
news.answers (*.answers archive-name: AudioFAQ/AmbisonicFAQ).

2. Corrections to the FAQ
=========================

E-mail comments and corrections to [e-mail]. Please
tell me which version you are commenting on.

The FAQ still contains one or two `?'s; if you can complete them, let
me know. If you have more information, please e-mail, post or fax it
to me.

Many thanks,
Martin Leese

University of New Brunswick
Department of Geodesy and Geomatics Engineering
Post Office Box 4400
Fredericton, N.B.
Canada E3B 5A3

E-mail: [e-mail]
WWW: http://www.omg.unb.ca/~mleese/
Tel: [phone]
Fax: [phone]

3. What is surround sound?
==========================

First there was mono with the sound emanating from a single
"point".

Then there was stereo with directional information spread along a
line in front of the listener.

In real life, of course, sound reaches our ears from all directions.
Surround sound attempts to improve the realism of the perceived
sound by providing information from all directions, not just from in
front of the listener.

4. What is Ambisonic Surround Sound?
====================================

Ambisonic Surround Sound is a set of techniques, developed in the
1970s, for the recording, studio processing and reproduction of the
complete sound field experienced during the original performance.
Ambisonic technology does this by decomposing the directionality of
the sound field into spherical harmonic components, termed W, X, Y
and Z. The Ambisonic approach is to use all speakers to
cooperatively recreate these directional components. That is to say,
speakers to the rear of the listener help locate sounds in front of the
listener, and vice versa.

Ambisonic technology is based on a meta-theory (a theory of
theories) of sound localisation developed by the late Michael A
Gerzon when he was with the Mathematical Institute, University of
Oxford (see the Gerzon 1992a reference). Ambisonic decoder design
aims to satisfy simultaneously and consistently as many as possible
of the mechanisms used by the ear/brain to locate sounds. The
Gerzon theory takes account of non-central as well as central
listening positions.

In an Ambisonic decoder the spherical harmonic direction signals,
W, X, Y and Z, are passed through a set of shelf filters which have
different gains at low and high frequencies designed to match
different ways the ear/brain locates sounds. (The different
localisation mechanisms operate below and above about 700 Hz.) The
speaker feeds are then derived by passing the outputs from the shelf
filters through a simple amplitude matrix. An important aspect of
Ambisonic decoder technology is that it is only at this final stage of
processing that the number and layout of speakers is considered.

The listening area for Ambisonic Surround Sound is comparable
with that for conventional stereo, but larger.

5. What are W, X, Y and Z?
==========================

With Ambisonic technology, the directionality of the sound field is
composed of spherical harmonic components. The zero-order
component is termed W and is omnidirectional. The first-order
components are figure-of-eight (lemniscate) responses which point
forward, left and up. These are termed X, Y and Z, respectively. In
practice, second-order and higher components are ignored.

The W, X, Y and Z channels are collectively called B-Format.

The fact that the Z component can be recorded creates the
opportunity for periphonic (full-sphere) reproduction. Periphony
requires speakers to be placed above and below the height of the
listeners' ears.

Readers familiar with microphone techniques will realise that the W
and Y spherical harmonic components are equivalent to the M and S
components of the M-S stereo recording technique. Ambisonics is a
natural extension of this recording technique to three dimensions.

6. How does Ambisonics differ from quadraphonics?
=================================================

Quadraphonics was a collection of incompatible systems introduced
in the 1970s. The collection included SQ, QS, UMX and CD-4. As
the name suggests they assumed four channels/speakers, and usually
assumed that the speakers would be 90 degrees apart. (Compare this
with the 60 degrees between speakers in stereo.) The systems strived
for channel separation and were characterised by the
ping-pung-pang-pong effects they reproduced. While these effects
were extremely novel and entertaining, they were also the antithesis
of fatigue-free realistic sound reproduction.

In contrast, Ambisonics attempts to recreate for the listener the
complete sound field of the original performance. A particular
number of speakers is not assumed and the technology can use
various numbers and speaker layouts. With the Ambisonic Surround
Sound system all of the speakers cooperate to locate a sound in its
correct position.

A problem with the quadraphonic systems was that they did not
work, and could never have been made to work because they were
based on false premisses. This is explained in detail in the
Sommerwerck 1984 reference, part I. In contrast, Ambisonics does
work.

7. How does Ambisonic Surround Sound differ from the
====================================================
Dolby surround systems?
=======================

Dolby Laboratories Inc have two surround systems of relevance to
the domestic listener, Dolby MP and Dolby Surround AC-3. Dolby
MP is described in the excellent article Introduction to [Dolby]
surround sound written by Bob Niland, [e-mail] and available by
anonymous FTP from ftp.csn.org in the file /Laserdisc/ld03 (ie, from
file://ftp.csn.org/Laserdisc/ld03). This suggests that:

 Dolby Motion Picture matrix encoding (Dolby MP) is an
 encoding system, similar to the SQ quadraphonic system,
 designed for motion picture sound tracks. Four channels are
 encoded - left, centre, right and a mono surround channel.
 Dolby Stereo is the result of this encoding. Dolby Surround is
 a decoding process designed to decode Dolby Stereo in the
 living room. Pro Logic is an active decoding process, also
 designed for the living room. Lucasfilm Home THX is an
 enhancement of Pro Logic.

Dolby Surround AC-3 is described in technical publications
available from Dolby Laboratories Inc, [e-mail], and on the
Dolby WWW page (http://www.dolby.com/). These suggest that:

 AC-3 is a digital encoding technique that exploits "audio
 masking" to achieve high bit-rate reductions. AC-3 can be
 used to encode between 1 and 5.1 audio channels. Dolby Stereo
 Digital film sound format uses AC-3 to encode 5.1 audio
 channels onto film stock. The 5 channels, left, centre, right,
 right surround and left surround, are all full bandwidth. The .1
 channel is a band limited (20 Hz to 120 Hz) bass effects
 channel. Dolby Surround AC-3, also called Dolby Surround
 Digital, is the consumer equivalent of Dolby Stereo Digital
 film sound and is also based on AC-3 coding of 5.1 channels.

The Dolby surround systems are designed to enhance the enjoyment
of motion pictures in cinemas. At this very limited task they are very
good. Ambisonic Surround Sound differs from the Dolby surround
systems in that it is designed for the realistic reproduction of music;
this is much more challenging.

8. What were Matrix H and HJ?
=============================

Matrix H and HJ were surround sound encodings used by the British
Broadcasting Corporation in the late 1970s for experimental FM
radio broadcasts. Matrix H was based on the QS quadraphonic
system and was modified to HJ which was based on Ambisonic
principles. The system was not adopted by the BBC because some
mono transmissions sounded "phasey". The other rumoured problem
was that someone high-up in the BBC thought that sound engineers
might have to be paid more if they worked with twice as many
speakers.

The `H' has no meaning. The BBC called the first matrix they
assessed Matrix A, and then worked up the alphabet.

9. What is UHJ?
===============

The Ambisonic format recommended for recording and studio
processing is called B-Format and is just the W, X, Y and Z
direction signals. If only horizontal surround sound is required, then
the Z signal can be omitted. However, this destroys the possibility of
periphonic (full-sphere) reproduction.

Established transmission media (LP, FM radio, CD) are all
two-channel and, unfortunately, it is impossible to obtain reasonable
surround sound using only two of the B-Format signals. To
overcome this, two-channel UHJ matrix encoding was developed.
Not only can two-channel UHJ be decoded back into horizontal
surround sound, but also this C-Format is mono and stereo
compatible.

When two-channel UHJ is played in stereo, the front- and
side-stage material is reproduced with sharply defined images. The
rear-stage material is reproduced, but given a less focused, more
"recessed" quality. This helps to provide an audible distinction
between front and rear sounds when played in stereo.

When two-channel UHJ is played in mono, sounds from all
directions, including due back, are reproduced in the single speaker at
a level within 5 dB of one another.

Two-channel UHJ was extended into a hierarchy of C-Formats for
2, 2.5, 3 and 4 transmission channels, termed BHJ, SHJ, THJ and
PHJ, respectively. The extra channels are used to augment the two
base channels to give improved horizontal surround sound and, for
four-channel UHJ (PHJ), periphonic (full-sphere) surround sound. In
practice, only two-channel UHJ (BHJ) encoded material has ever
been released. For this reason UHJ has become a synonym for BHJ,
and UHJ is the symbol you will see on LPs and CDs.

The advantages of UHJ over B-Format are that it is mono and stereo
compatible, and allows horizontal surround sound to be transmitted
using two-channel media. The disadvantages of UHJ are that both
encoding and decoding require the use of 90 degree phase shifters,
and that encoding into only two channels requires compromise.
("No-compromise" horizontal surround sound requires three
transmission channels.)

It is UHJ which has caused Ambisonics to be described as a "matrix"
system, but Ambisonics is much more than UHJ.

Readers interested in seeing the set of encoding/decoding equations
should consult the appendices of the Gerzon 1985 reference.

UHJ is more symbolism than initialism. The `U' stands for
Universal, and is taken from the UMX quadraphonic system which
pioneered the technique of using supplementary channels to enhance
directional resolution. The `H' represents the BBC's Matrix H and
their work on mono and stereo compatible matrices. The `J' is taken
from System 45 J, the name of the original two-channel UHJ
system. (The `J' was simply a code letter used to describe a possible
surround sound system.)

10. What are BHJ, SHJ, THJ and PHJ?
===================================

BHJ is the engineering specification for encoding the W, X and Y
direction signals into two channels. The two channels, called Left
and Right, can then be transmitted using conventional stereo media
before being decoded back into W, X and Y. The BHJ format has
been designed to be mono and stereo compatible. In practice, BHJ is
the only UHJ encoding that has been used for commercial record
releases. For this reason UHJ has become a synonym for BHJ and
UHJ is the symbol you will see on BHJ encoded LPs and CDs.

SHJ specifies how W, X and Y can be encoded into 2.5 channels,
called Left, Right and T, where the T channel is of reduced
bandwidth (5 kHz). The original intention was to provide the reduced
bandwidth channel in broadcasting by additional modulation of the
38 kHz sub-carrier. Presumably RDS, Minicall, etc, kills this
possibility.

THJ specifies how W, X and Y can be encoded into three channels
called Left, Right and T. This is the "no-compromise" horizontal
C-Format.

PHJ specifies how W, X, Y and Z can be encoded into four channels,
called Left, Right, T and Q, and is the "no-compromise" periphonic
C-Format. Periphonic (full-sphere) reproduction requires speakers
to be placed above and below the height of the listeners' ears.

BHJ, SHJ, THJ and PHJ are all inter-compatible. That is to say, to
go from one member of the set to the next you add or delete
additional signals without changing those that remain. A beauty of
this is that each member of the UHJ set is mono and stereo
compatible. In addition, a BHJ decoder, for example, can decode
SHJ, THJ and PHJ material simply by ignoring the extra T and Q
channels.

Version 1.0 of this FAQ suggested encoding a third channel into the
`subcodes' of a CD to give THJ or SHJ. It transpires that the
bandwidth available in the subcodes is less than 2 kHz using 16 bits,
so this ain't gonna fly.

It is possible, however, to use "buried data" to encode a third channel
of reduced bandwidth onto a CD such that an existing CD player is
unaware the channel exists. This would allow SHJ encoded CDs to be
produced that are completely compatible with conventional stereo
CD players. That is to say, a stereo system would produce stereo, a
BHJ decoder would produce surround sound, and an SHJ decoder
(fed from a CD player with special digital electronics) would
produce even better surround sound. All this from the same CD! The
technique is too complicated to describe here, and interested readers
should consult the Gerzon and Craven 1995 reference.

Peter Knight has pointed out that the CD format specification
includes a four-channel quad format that would be suitable for PHJ
encoded material. The problem, of course, is that existing CD players
are not quad CD "aware" and would produce a mishmash if asked to
play a quad CD. He has also pointed out that quad CDs have to be
spun twice as fast as stereo CDs and have only half the playtime.

11. Are UHJ encoded CDs available?
==================================

Yes.

A discography of 160 or so UHJ encoded record releases is available
on the WWW at http://www.omg.unb.ca/~mleese/. In addition, it is
available by anonymous FTP from ftp.omg.unb.ca (131.202.34.4) in
the directory /pub/ambisonic/ (ie, from
file://ftp.omg.unb.ca/pub/ambisonic/). I am also happy to e-mail
copies to people. The discography was compiled by Eero Aro and is
being maintained by Mark Anderson. It is not complete and updates
are requested; details on how to do this are given at the beginning of
the discography.

12. What happens with stereo sources (conventional LPs,
=======================================================
CDs, etc)?
==========

Domestic Ambisonic decoders feature a Super Stereo button for
decoding stereo sources. This uses the rear part of the sound field to
reinforce the location of sounds in front of the listener. In addition,
any ambience present in the source will be directed all around the
listener, although the effectiveness of this depends greatly on the
recording technique that was used. The Super Stereo mode also
includes a stereo width control which allows the stereo image to be
compressed to mono-like or expanded into a horseshoe around the
listener.

13. Can Ambisonics decode Dolby MP?
===================================

No, not really.

A key part of Ambisonic decoding is the use of shelf filters. These
give different gains at low and high frequencies to satisfy different
mechanisms used by the ear/brain to locate sounds. (The change
occurs at around 700 Hz.) Dolby MP encoding is similar to the SQ
quadraphonic system and, unfortunately, SQ decoding requires that
no shelf filters be used. As a consequence, SQ (and therefore Dolby
MP) decoders cannot be designed to give full Ambisonic results;
there is even a mathematical theorem to this effect.

Integrex Limited manufactured an Ambisonic decoder which could
decode almost every quadraphonic system, including SQ. The design
of this decoder has been published (see the Gerzon 1977b reference),
and the SQ mode used Ambisonic technology only to give more
freedom over the number and layout of speakers.

Of course, there is nothing to prevent you reproducing Dolby MP
encoded material through an Ambisonic UHJ or Super Stereo
decoder. The seamless coherent sound field which results has been
described as "superb", but it will not be what the sound engineer who
created the recording intended you to hear. The question of whether
Ambisonic decoding of Dolby MP encoded material is preferable, is
most easily answered by listening.

Dolby MP will always suffer from non-existent sound imaging to
the rear and side of the listener. While not a serious impediment to
the enjoyment of motion pictures, these limitations do make Dolby
MP encoding unsuitable for music. I am old enough to remember
SQ; like all the quadraphonic systems, it sucked.

It is also strange that the Dolby MP crowd seems determined to
repeat the mistakes made by the quadraphonic crowd, namely a
desire for channel separation (which merely calls attention to
individual speakers as sources of sound) and a penchant for active
decoders (which cause fatigue in listeners).

14. Can Ambisonics decode Dolby Surround AC-3?
==============================================

Yes, and I am sure that Dolby Surround AC-3 would benefit from it.

Dolby Surround AC-3 does not use matrixing and the five audio
channels have complete separation. Sadly, this is not sufficient for
realistic surround sound reproduction, the problem being the
"pair-wise" mixing style. Dolby Surround AC-3 is just a delivery
mechanism and is not tied to pair-wise mixing, however, to date all
Dolby Surround AC-3 movie sound tracks have been mixed using
the pair-wise mixing style.

Pair-wise mixing is also called "pan-potting", "amplitude mixing"
and "intensity stereophony". It mixes signals into the feeds for a pair
of speakers to create the illusion that a sound is coming from a point
somewhere between the speakers. During mixing, the apparent
location of each sound is determined only by the relative amplitude
of that sound in the two speakers. Almost all stereo recordings are
mixed using the pair-wise mixing style.

The ear/brain locates sounds using phase differences between the ears
as well as amplitude differences. (Phase is used to locate sounds with
frequencies between 150 Hz and 1.5 kHz, amplitude for frequencies
between 300 Hz and 5 kHz, and other cues for frequencies above 2.5
kHz. Note that the three frequency ranges overlap.) Fortunately,
when a pair of speakers are in front of the listener and separated by
60 degrees or less, the amplitude changes mimic the correct phase
changes and the pair-wise mixing style works well. Unfortunately,
pair-wise mixing works poorly when the speakers are to the rear of
the listener and not at all when they are to one side. (See the Gerzon
1985 or the Fellgett 1981 reference. Better still, try it yourself!)
This means that any surround sound system that relies on pair-wise
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
mixing between adjacent speakers must fail. This is as true for
+++++++++++++++++++++++++++++++++++++++++++
Dolby Surround AC-3 as it was true for the quadraphonic systems.
Such absolute statements can be made because the way that the
ear/brain localises sound has not changed.

One solution is for sound engineers to use a mixing style other than
pair-wise mixing to mix the Dolby Surround AC-3 format.
Happily, an alternative exists - Ambisonics.

Another poorer solution is for the 5.1 pair-wise mixed channels to
be converted into W, X, Y and additional signals, and to then use
Ambisonic technology to reproduce the sound field. This is described
in the Gerzon 1992b reference.

As with Dolby MP, these limitations of pair-wise mixing are not a
serious impediment to the enjoyment of motion pictures. They do,
however, make pair-wise mixed Dolby Surround AC-3 unsuitable
for music.

15. Can Ambisonics make use of Music DVDs?
==========================================

A consortium has announced a Digital Versatile Disc format which
can contain either 13 or 27 times as much data as the current audio
CD format. (The higher figure is for a double-sided double-layered
disc.) The proposal for an audio-only version of DVD, called
High-Quality Audio Disc, has been released by the Acoustic
Renaissance for Audio. The proposal, which is available on the ARA
WWW page, is for:

 o Full 3-D surround sound with up to six channels as well as a
   separate (conventional) two-channel feed.
 o Sampling at either 48 kHz or 96 kHz.
 o Up to 24 bits of precision. (Normally 20 bits would be used
   with 48 kHz sampling and 16 bits with 96 kHz.)
 o The use of lossless compression, termed `packing'.
 o A trade-off, decided upon by the record producer, between
   precision, frequency bandwidth, number of channels and
   playing time.

To carry Ambisonic Surround Sound the proposal suggests encoding
the W, X, Y and Z signals onto the Music DVD as a set of five feeds
for speakers arranged in a regular pentagon, plus an optional height
channel. These either can be reproduced directly using the standard
five speaker layout, or the W, X, Y and Z channels can very simply
be reclaimed for processing by an Ambisonic decoder. I guess that
the five speaker feeds will not include psychoacoustic shelf filtering.

HQAD is the first real opportunity for periphonic (full-sphere)
Ambisonic source material to be released commercially. A
periphonic decoder was demonstrated as long ago as 1980, but to date
domestic full-sphere surround sound reproduction has been enjoyed
only by a few enthusiasts with access to Ambisonic master tapes. The
advent of HQAD and its accommodation of Ambisonics will, for the
first time, bring full-sphere surround sound within the reach of
everybody.

The advantages of periphony over horizontal surround sound are not
only the possibility of using height for special effects but also that
recordings sound more lifelike and less "hi-fi". For example, the
timbre of orchestral instruments take on the "feathery" quality heard
at live events.

Practical periphony requires six or eight speakers, some of which
must be placed above and below the height of the listeners' ears.
Readers interested in seeing the various speaker layouts which are
possible should consult the Gerzon 1980 reference.

Of course, horizontal Ambisonic decoders will still be able to
produce "no compromise" horizontal surround sound simply by
ignoring the Z (height) signal.

Copies of A Proposal for the High-Quality Audio Application of
High-Density CD Carriers (Version 1.2) can be obtained from:

 J R Stuart, Chairman ARA
 c/o the Secretariat
 Acoustic Renaissance for Audio
 Stonehill
 Stukely Meadows
 Huntingdon
 Cambridgeshire
 United Kingdom
 Tel: [phone]
 Fax: [phone]
 E-mail: [e-mail]
 WWW: http://www.meridian.co.uk/ara/

 Hirokazu Negishi, Founder ARA
 Research & Development Headquarters
 Cannon Inc Shinjuku Office
 7-1 Nishi-Shinjuku 2-chome
 Shinjuku-ku
 Tokyo 163-07
 Japan
 Tel: [phone]
 Fax: [phone]
 E-mail: [e-mail]

16. Have Ambisonic decoders been manufactured
=============================================
commercially?
=============

Yes.

Minim Electronics Limited marketed a range of three decoders, the
AD 7, AD 8 and AD 10, and also a printed circuit board module for
enthusiasts to incorporate into their own projects.

IMF Electronics assisted in the development of Ambisonics and
manufactured a decoder, the D20B. Part of the company was
resurrected under the name TDL Electronics Limited, but it is
unlikely that they have had any interest in Ambisonics.

 TDL Electronics Limited
 Unit 2, Pilot Trading Estate
 High Wycombe
 Buckinghamshire
 United Kingdom
 Tel: [phone]
 Fax: [phone]

Up to 1981, Integrex Limited offered an Ambisonic decoder which
could decode SQ, QS, UMX and Matrix H/HJ as well as UHJ. The
Company is alive and kicking, but no longer has any involvement in
Ambisonics or the hi-fi business.

 Integrex Limited
 Portwood Industrial Estate
 Church Gresley
 Derbyshire DE11 9PT
 United Kingdom
 Tel: [phone]
 Fax: [phone]

Abacoid Limited produced a Professional Ambisonic Decoder, the
PAD 9211. Does anybody know if the Company still exists? The
telephone number listed in previous versions of this FAQ is no
longer a business number.

 Abacoid Limited
 110A St Margarets Road
 Hanwell
 London W7 2HF
 United Kingdom

Troy manufactured an Ambisonic Processor [Decoder], the TA 110P,
for use in the car. They currently have no plans to restart
manufacture.

 Alan Sexton
 Troy
 Charters Road
 Sunningdale
 Ascot
 Berkshire SL5 9QD
 United Kingdom
 Tel: [phone]

NAD developed inexpensive Ambisonic decoders. Does anybody
know if they were ever offered for sale? The telephone number listed
in previous versions of this FAQ is no longer a business number.

 NAD
 683 High Street
 North Finchley
 London N12
 United Kingdom

And one for our antipodean readers; Audiotech Industries offered an
Ambisonic decoder. Details anyone?

 Audiotech Industries
 PO Box 8756
 Auckland
 New Zealand
 Tel: [phone]

17. Are Ambisonic decoders being manufactured
=============================================
commercially?
=============

Yes.

By Minim Electronics Limited. When I last spoke to them in January
1995, they were about to revamp their offerings.

 Minim Electronics Limited
 Lent Rise Road
 Burnham
 Slough SL1 7NY
 United Kingdom
 Tel: [phone]

Cepiar Limited manufacture a reference Ambisonic decoder, the
Ambi-8x. This is intended for professional use, and is priced
accordingly. Using plug-in resistor boards, the decoder can be
configured for 4, 5, 6, 7 or 8 speakers, and for horizontal or
periphonic (full-sphere) surround sound. Cepiar also plan to release a
consumer Ambisonic decoder in the second half of 1996.

 Cepiar Limited
 Debden House
 11 St Ethelwold's Close
 Ely
 Cambridgeshire CB6 3AX
 United Kingdom
 Tel: [phone]
 Fax: [phone]

In March 1993, Sound & Vision (see References) reviewed the Onkyo
TX-SV909PRO A/V Receiver which incorporates an Ambisonic
decoder. When in Ambisonic mode, the receiver is configured only
for four speakers. The successor to the Onkyo 909PRO is the Onkyo
919THX, but this does not incorporate an Ambisonic decoder.

 Onkyo USA Corporation
 200 Williams Drive
 Ramsey
 NJ 07446
 USA
 Tel: [phone]
 Fax: [phone]

 Onkyo Europe GMBH
 Hellersbergstrasse 4
 4040 Neuss
 Germany
 Tel: [phone]
 Fax: [phone]
 Telex: 8517916 ONDU D

Meridian's 565 DSP Surround Processor, which can be configured
for 4, 5, 6 or 7 speakers, incorporates an Ambisonic decoder.

 Meridian Audio Limited
 Stonehill
 Stukely Meadows
 Huntingdon
 Cambridgeshire
 United Kingdom
 Tel: [phone]
 Fax: [phone]
 E-mail: [e-mail]
 WWW: http://www.meridian-audio.com/

 Meridian America Inc
 3800 Camp Creek Pkwy.
 Suite 112, Bldg. 2400
 Atlanta
 GA 30331
 USA
 Tel: [phone]
 Fax: [phone]

The October 1995 issue of Audio magazine contained an annual
equipment directory that included Sansui and Legacy Audio as
suppliers of Ambisonic receivers and decoders, respectively. The
Sansui receiver, model RZ2900, does not have an Ambisonic mode,
so this was a misprint.

When I last spoke to Legacy Audio in July 1996, they had decided
against adding an Ambisonic mode to their Steradian product.

 Legacy Audio
 3021 Sangamon Ave
 Springfield
 IL 62702
 USA
 Tel: [phone] (also 1-800-283-4644)
 Fax: [phone]

Version 2.2 of this FAQ suggested that Maplin Electronics plc
offered an Ambisonic decoder kit. This was incorrect. In 1994,
Electronics - The Maplin Magazine carried a series of articles on
surround sound (see the Woodgate 1994 reference), but referred
readers to Minim Electronics Limited for the supply of Ambisonic
decoders.

If anybody knows of other domestic Ambisonic decoders, will they
please let me know. I am particularly interested to hear about stand
alone Ambisonic decoders that are not bundled together with home
theatre decoders.

18. If Ambisonics is so wonderful, why is it not a
==================================================
commercial success?
===================

We should first note that technical excellence and commercial
success do not necessarily go hand-in-hand. This is why you are all
watching VHS video tapes and not Betamax.

Ambisonics has suffered from the following:

 o It came to market just as quadraphonics was dying away.
   Manufacturers had lost a bundle on quadraphonics and were
   not receptive to "yet another" surround sound system.
 o It was never supported by a major record company. The
   record majors had all backed different quadraphonic systems.
 o The rights were held by the National Research Development
   Corporation, now defunct. This was a sort of venture capital
   company, but one owned and run by the British government.
   The NRDC has little commercial nous. (Yes "nous", look it
   up.)
 o Ambisonics is subtle; it does not lend itself to the dramatic
   ping-pung-pang-pong effects beloved by salespeople. This
   makes it difficult to sell.
 o Ambisonics is thought of as a "purist" technique and not
   applicable to multi-track studio recording. This fallacy is
   demolished by Alan Parsons Stereotomy, Arista 8384.
 o It is British, ie, not invented in the USA or Japan.
 o It is British, ie, not well marketed.

19. How many speakers does Ambisonics use?
==========================================

A major advantage of Ambisonic Surround Sound is that recording
and studio processing are disengaged from reproduction. The former
produce and operate on the W, X, Y and Z channels, but these can be
reproduced through any number of speakers. The more speakers
which are used the better, as this gives a larger listening area and a
more stable sound localisation. Using more speakers also improves
the illusion that the speakers have vanished; that is to say, the
listeners hear a single seamless sound field. For horizontal surround
sound a minimum of four speakers is required.

Ambisonic technology places restrictions on the choice and
placement of speakers. Specifically:

 o The speakers (power-amps) should have similar efficiencies
   (gains) and phase responses. The easiest way to achieve this is
   to use identical units.
 o All speakers (and power-amps) should cover the full
   frequency range. Unlike Dolby MP, there is no "surround
   channel" and it is not band limited.
 o Four speakers are placed in a rectangle, preferably with the
   longer side running front to back, all facing a point in the
   centre of your living room. A "layout" control compensates
   for different aspect ratios. The four speakers can be driven
   from either three or four power-amps.
 o Five speakers are placed in a regular pentagon, all facing the
   central point. They are driven from five power-amps.
 o Six speakers are placed in a regular hexagon, all facing the
   central point. They can be driven from between four and six
   power-amps.
 o A speaker (or speakers) can be moved closer to the central
   point, but should then be fed through a delay line (or lines).

Some diagrams would be useful here.

The disadvantage of using only four speakers is that sounds with
spiky waveforms (audience applause, harpsichords, oboes) tend to be
drawn away from their correct location and towards a speaker. Using
five or six speakers gives considerably more robust side and rear
imaging.

For periphonic (full-sphere) surround sound a minimum of six or
eight speakers is required driven from at least four or five
power-amps, respectively. Readers interested in seeing the possible
speaker layouts should consult the Gerzon 1980 reference.

Auditorium decoders that can drive between 8 and 128 speakers are
available (from Cepiar Limited). For domestic use the limiting
factors are the cost of the necessary speakers and power-amps, and
the practical problem of squeezing them into your living room.

The speaker feeds are each a simple weighted sum of the W, X, Y
and Z signals after they have passed through the shelf filters. Readers
interested in seeing the equation should consult the appendices of the
Gerzon 1985 reference.

With the "old-type" Ambisonic decoders described above, the
apparent position of the centre-front sound image varies as the
listener moves from one side of the living room to the other. This is
not a problem when reproducing music, but when used with TV the
on-screen sounds can become misaligned with the on-screen
pictures. "New-type" Ambisonic decoders, described in the Gerzon
and Barton 1992 reference, produce a stable centre-front sound
image that solves this problem. These decoders can be used with
irregular speaker layouts, either five speakers with one at the
centre-front or six speakers with two at the centre-front.
Alternatively, it is possible to use an additional channel to stabilise
the centre-front sound image, as described in the Gerzon 1992b
reference. These newer types of Ambisonic decoder are not yet
commercially available.

20. From where can I obtain more information?
=============================================

If you have a technical bent then you should obtain and read some of
the references listed in References (see References). I recommend
particularly the Gerzon 1985 reference. Next best are the Woodgate
1994 and Sommerwerck 1984 references.

If you want to know what Ambisonic Surround Sound sounds like,
but cannot arrange to hear it for yourself, the results of an extensive
domestic listening test are described in the Attewell 1982 reference.

Further information on Ambisonics is available from the Ambisonic
and `B'-format User Group run by Donald G Maclennan. ABUG is
an informal group of about 180 devotees. Donald keeps a database of
members' interests and he is happy to put people whose interests
overlap in touch with each other. The membership includes people
from the pro sound industry, journalism, academia, and individuals
like me who are just interested.

 Donald G Maclennan
 ABUG
 51 Hillside Avenue
 Plymouth
 Devon PL4 6PS
 United Kingdom
 Tel: [phone]
 Fax: by appointment

Interested readers might like to join an e-mail mailing list, called
sursound, devoted to surround sound audio discussion and research.
To join, send an e-mail message to [e-mail]
with the contents:

 subscribe sursound
 end

The list owner is Jim Rusby.

21. What about recording and studio processing?
===============================================

This FAQ is aimed at the domestic listener. Recording and studio
processing are two areas of Ambisonic technology that have been
omitted deliberately; the topics deserve an FAQ of their own, but
somebody else will have to create it. As an interim measure, this
Section lists the contact details of companies involved in these areas.
Please contact them directly; I do not work in the pro audio industry
and have limited knowledge of it. Be aware that, in general,
equipment designed for the pro audio market is more expensive that
domestic equipment.

SurroundWorks«
++++++++++++++

Recording of acoustic music by means of ambisonic surround
technology for current stereo reproduction as well as future surround
sound release. Employing the 24-bit Nagra-D digital multitrack and
the SoundField microphone, SurroundWorks is available in the
studio or on location either as a primary or as a secondary archival
production system.

 SurroundWorks«
 21 Millay Place
 Mill Valley
 CA 94941
 USA
 Tel: [phone]
 Fax: [phone]
 E-mail: [e-mail]
 Contact: Jeffrey Silberman

SoundField Ltd.
+++++++++++++++

Products: Multi-capsule microphone systems.

 SoundField Ltd.
 Charlotte Street Business Centre
 Charlotte Street
 Wakefield
 West Yorkshire
 United Kingdom
 WF1 1UH
 Tel: [phone]
 Fax: [phone]
 E-mail: [e-mail]
 WWW: http://www.proaudio.co.uk/sndfield.htm
 Contact: Richard Bacon - Technical Sales

AGM Digital (Deutschland)
+++++++++++++++++++++++++

Re-launch of four capsuled microphone array and processing system,
and Encoding and Decoding systems. Have a look at the web page for
the latest news.

 AGM Digital (Deutschland)
 Am Eisstadion 8
 D-82467 Garmisch-Partenkirchen
 Germany
 Tel: [phone]
 Fax: [phone]
 E-mail: [e-mail] (from 1 October 1996
 [e-mail])
 WWW: http://ourworld.compuserve.com/homepages/agm/
 (from 1 October 1996 http://www.agmworld.com/)
 Contact: Anthony G Morris

Lake DSP Pty. Ltd.
++++++++++++++++++

Digital signal processing hardware and software systems for audio
applications. These include tools for long convolution filtering and
room acoustic measurements, real-time acoustic simulation using
synthesised B-Format Ambisonics (with support for arbitrary sized
and shaped loudspeaker arrays and binaural decoding), and
comprehensive support for custom application programming.

 Lake DSP Pty. Ltd.
 Suite 1501
 33 Bligh St.
 Sydney, NSW, 2000
 Australia
 Tel: [phone]
 Fax: [phone]
 E-mail: [e-mail]
 WWW: http://www.lake.com/
 Contact: Leonard Layton

Audio Dimensions
++++++++++++++++

 Audio Dimensions
 22 Lisson Grove
 Mutley
 Plymouth
 Devon
 PL4 7DN
 United Kingdom
 Tel: [phone]
 Fax: [phone]
 E-mail: [e-mail]
 WWW: http://www.zynet.co.uk/audiodim/home.htm
 Contact: Chris Blythe

Cepiar Limited
++++++++++++++

 Cepiar Limited
 Debden House
 11 St Ethelwold's Close
 Ely
 Cambridgeshire CB6 3AX
 United Kingdom
 Tel: [phone]
 Fax: [phone]

22. References
==============

An extensive reference list on Ambisonics, compiled by the late
Michael A Gerzon and others, is available on the Internet (see
Section 1). I am also happy to e-mail copies of the list to people. The
references listed here are confined to those referred to in this FAQ
(plus one).

Michael Gerzon, 1977a, "NRDC surround sound system", in
Wireless World, April issue, pages 36 to 39.

Michael A Gerzon, 1977b, "Multi-system Ambisonic decoder", in
Wireless World. The design was in three parts:
Part 1: "Basic design philosophy", July issue, pages 43 to 47
Part 2: "Main decoder circuits", August issue, pages 69 to 73
Part 3: never published.

Michael A Gerzon, 1980, Practical Periphony: The Reproduction of
Full-Sphere Sound, presented at the 65th Audio Engineering Society
Convention, London, 25-28 February. Preprint 1571 (A6).

Prof P B Fellgett, 1981, "Ambisonics", in New Electronics, May
issue, pages 38, 44, 46 and 48.

Trevor Attewell, 1982, "Ambisonics - the future of surround
sound?", in Hi-Fi News & Record Review, Volume 27, number 9
(September issue), pages 53, 55, 56 and 58.

William Sommerwerck, 1984, "Ambisonics Comes of Age", in The
Audio Amateur:
Part I: issue 3, pages 7 to 13 and page 58
Part II: issue 4, pages 38 to 45
Part III: issue 5, pages 36, 37, 40, 41 and 42.

Michael A Gerzon, 1985, "Ambisonics in Multichannel Broadcasting
and Video", in the Journal of the Audio Engineering Society, Volume
33, number 11 (November issue), pages 859 to 871.

Michael A Gerzon, 1992a, General Meta theory of Auditory
Localisation, presented at the 92nd Audio Engineering Society
Convention, Vienna, 24-27 March. Preprint 3306.

Michael A Gerzon, 1992b, Hierarchical System of Surround Sound
Transmission for HDTV, presented at the 92nd Audio Engineering
Society Convention, Vienna, 24-27 March. Preprint 3339.

Michael A Gerzon and Geoffrey J Barton, 1992, Ambisonic Decoders
for HDTV, presented at the 92nd Audio Engineering Society
Convention, Vienna, 24-27 March. Preprint 3345.

"Onkyo TX-SV909PRO A/V Receiver", in Sound & Vision, 1993,
Volume 8, number 6 (March issue), page 14. This receiver
incorporates an Ambisonic decoder.

Ian G Masters, 1993, "Ambisonics", in Sound & Vision, Volume 8,
number 6 (March issue), pages 26 and 43.

J M Woodgate, 1994, "Surround Sound - Fad or Fancy?", in
Electronics - The Maplin Magazine.
Part One: "The First Four Channels", July issue, pages 46 to 51
Part Two: "Multichannel and Ambisonics", August issue, pages 66 to
70
Part Three: "Dolby Surround and THX", September issue, pages 52
to 61.

M A Gerzon and P G Craven, 1995, "A High Rate Buried Data
Channel for Audio CD", in the Journal of the Audio Engineering
Society, Volume 43, number 1/2 (January/February issue), pages 23
to 28.

23. Acknowledgements
====================

Many thanks to the following people for contributing to the FAQ:

 Rustan Finndin, [e-mail]
 Peter Knight, [e-mail]
 Jun Guo, [e-mail]
 Jeffrey Silberman, [e-mail]
 Jimmy T Rusby, [e-mail]
 Dave Malham, [e-mail]
 Brian Lenharth, [e-mail]
 David S Monett, deceased
 Peter G Craven, [e-mail]
 Michael A Gerzon, deceased
 William Sommerwerck, [e-mail]
 Roger Dressler, [e-mail]
 Eero Aro, [e-mail]
 Mark Anderson, [e-mail]
 Geoffrey Barton, [e-mail]
 Barry Fox, [e-mail]

24. Trademarks
==============

Ambisonics is a trademark of Nimbus Records.

The following are registered trademarks of Dolby Laboratories
Licensing Corporation:

 Dolby
 Dolby Surround
 AC-3
 Pro Logic (no hyphen)
 Dolby Stereo

For more information contact Lily Cheung, Dolby's Intellectual
Property Manager, [e-mail].

Lucasfilm and Home THX are both registered trademarks of
Lucasfilm Ltd, whether used together or separately.

SurroundWorks is a registered trademark of Jeffrey Silberman.

PostScript is a trademark of Abobe Systems Incorporated or its
subsidiaries which may be registered in certain jurisdictions.

Mosaic is a proprietary trademark of the University of Illinois.

The following are not definitive in that I have been unable to contact
directly the companies concerned. If anybody has e-mail or WWW
addresses for them, please let me know.

DVD is a trademark of Toshiba.

QS is a trademark of Sansui.

SQ is a trademark of CBS Laboratories.

CD-4 is a trademark of Japan Victor (JVC).

Does anybody know if UMX is a trademark?

25. Obituary
============

Michael A Gerzon was the "Brains" behind Ambisonic Surround
Sound. This obituary, written by Barry Fox, first appeared in The
Guardian newspaper in the United Kingdom. It is reproduced with
permission.

Michael Gerzon
++++++++++++++

Born 4 December 1945. Died 6 May 1996.
--------------------------------------

Mathematician and audio expert Michael Gerzon died earlier this
week, at the age of fifty, after years of struggling against two
different illnesses that would each have wrecked a lesser man. After
a spell at the Mathematical Institute in Oxford, he had been working
for twenty years as a consultant on a wide range of digital audio,
video and computer projects.

Gerzon's partner on many projects, Peter Craven, sums up the
tributes that have been circulating on the Internet and explains why
few people outside the electronics industry will have heard of him:
"What Michael does now the world will want in thirty years time".

I first came across Michael Gerzon in the early seventies, when the
absurd quadraphonics standards battle was raging. At least four
electronics and record companies had developed surround sound
systems which claimed to squeeze four channels of hi-fi into the
groove of a stereo LP, for reproduction through four loudspeakers,
one at each corner of the living room.

Record company CBS (later bought by Sony) had hired a large
conference room in a Park Lane hotel to demonstrate its SQ system.
We heard a demonstration of sound effects rattling round the room
and got the chance to pretend we were sitting in the middle of an
orchestra. The CBS people then launched into a highly technical
explanation of why SQ was better than the systems which their
Japanese rivals had developed. They talked a lot of mathematics
about "vectors" and it sailed right over our heads.

From the back of the room, a lanky young man stood up, holding a
flimsy square cage made out of wire. He turned it inside out to
explain vectors in gloriously simple language. Gerzon's point was
that although SQ might sound good with some musical material, like
that used for the demonstration, mathematical theory proved that
there would always be more music that would sound wrong.

In later years I never ceased to marvel at the way Gerzon could make
even the most complicated concept easy to understand. He pitched his
explanation at exactly the level of whoever he was talking to,
without ever sounding even slightly patronising.

During the seventies, relations between CBS and Michael Gerzon got
progressively worse. Every time CBS would give a lecture at a
recording industry seminar, Michael would pop up and ask questions
which demolished the theory. He wasn't doing it for fun, or to look
clever, or to harm CBS. He was doing it because he firmly believed,
and had the maths to prove it, that none of the quadraphonics systems
would be right for hi-fi in the home.

Behind the scenes, complaints were lodged with the Oxford
authorities and Gerzon was carpetted. He continued to speak his
mind and this may well have cost him an academic career.

Gerzon's arguments carried special weight because he was not just a
maths theorist. He loved music, of all types, and made many live
recordings as a hobby. He also had very acute hearing. He could hear
much higher frequencies (up to 23 kHz) than most people. He
attributed this to his very serious asthma.

It was inevitable that Gerzon would develop his own surround sound
system. It was called Ambisonics and he worked on it with several
other academics and recording engineers. Gerzon rethought the
theory of something we take for granted; just a few loudspeakers can,
with a carefully made recording, create the illusion of a wide natural
spread of sound. Ambisonics widened the spread to surround the
listener.

The system was backed by the UK's National Research Development
Corporation (which later became the British Technology Group) but
never took off. The NRDC never seemed to understand the consumer
electronic market, and missed the opportunity to team up with Dolby
Laboratories and market home equipment that offered the choice of
Ambisonics for playing music CDs with subtle fidelity and Dolby
surround for the blockbuster home cinema effects that are now all
the rage.

In the eighties Gerzon moved onto digital audio and video, laying the
foundation for many of the systems which the industry now takes for
granted. With Peter Craven he wrote the theory for noise shaping,
which lets recording studios squeeze higher fidelity onto CDs. His
last work was for a voluntary industry group, the Acoustic
Renaissance for Audio.

The ARA's aim is to persuade the Japanese electronics industry to
look ahead into the next century and set standards for future variants
of CD that will deliver super-hifi. The key to this promise is a
digital technique called lossless coding and Gerzon and Craven were
at the final stages of research when he was rushed to hospital and
died.

The work will go on, and few people outside the audio industry will
notice Gerzon's passing. But sometime in the future, around 2026,
engineers will be trying to patent inventions that they think are new
and repeatedly finding that Michael Gerzon had got there first.



End of Ambisonic Surround Sound FAQ