13. Can Ambisonics reproduce Dolby MP?
Description
This article is from the Ambisonic Surround Sound FAQ, by Martin Leese with numerous contributions by others.
13. Can Ambisonics reproduce Dolby MP?
Dolby MP encoding, and Dolby Surround and Pro Logic decoding, are all
described in the excellent article, Introduction to [Dolby] surround
sound written by Bob Niland. The article suggests that:
Dolby Motion Picture matrix encoding (Dolby MP) is an encoding
system designed for motion picture sound tracks. Four channels are
encoded - left, centre, right and a mono surround channel. Dolby
Stereo is the two-channel 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.
A Dolby MP encoded source is intended to be reproduced through a Dolby
Surround or Pro Logic decoder. These assume rear speakers arranged
only to create a reverberant sound field (typically, bipolar speakers
facing the walls), and the use of a time delay to ensure that front
sound effects are not localised to the rear.
Ambisonics is not limited to creating a reverberant rear sound field,
and requires a different arrangement of speakers. Also, with
Ambisonics all speakers cooperate to localise sounds, so the
front-rear time delay is unnecessary (and would be detrimental).
Dolby Surround and Pro Logic decoders 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 them unsuitable for music.
Of course, there is nothing to prevent you reproducing Dolby MP
encoded material through an Ambisonic UHJ or Super Stereo
decoder. Many people prefer this, and describe the seamless coherent
sound field which results as "superb". But it will not be what the
sound engineer who created the recording intended you to hear.
Continue to:
My Books
