16. Can Ambisonics make use of DVD?
Description
This article is from the Ambisonic Surround Sound FAQ, by Martin Leese with numerous contributions by others.
16. Can Ambisonics make use of DVD?
A consortium has announced a Digital Versatile Disc format which can
contain between 6 and 22 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 Web page, is for:
* Full 3-D surround sound with up to six channels as well as a
separate (conventional) two-channel feed.
* Sampling at either 48 kHz or 96 kHz.
* Up to 24 bits of precision. (Normally 20 bits would be used with
48 kHz sampling and 16 bits with 96 kHz.)
* The use of lossless compression, termed "packing".
* 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 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 has the "feathery" quality heard at
live events.
Practical periphony requires a minimum of 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 1.3) can be obtained from:
J R Stuart, Chairman ARA
c/o the Secretariat
Acoustic Renaissance for Audio
Stonehill
Stukely Meadows
Huntingdon
Cambridgeshire PE18 6ED
United Kingdom
Phone: +44-1480-52144
Fax: +44-1480-451587
E-mail: araAT_SINGmeridian-audio.com
Web: <http://www.meridian-audio.com/ara/>
Hirokazu Negishi, Founder ARA
Research & Development Headquarters
Cannon Inc Shinjuku Office
7-1 Nishi-Shinjuku 2-chome
Shinjuku-ku
Tokyo 163-07
Japan
Phone: +81-3-3344-8409
Fax: +81-3-3349-1399
E-mail: negishiAT_SINGgcds.cannon.co.jp
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