Progress in 5-2-5 Matrix Systems
David Griesinger
Lexicon
3 Oak Park
Bedford MA 01730
Abstract
A high quality 5-2-5 matrix encoder and decoder system offers the prospect of
inexpensive compatible media for multichannel sound. The advantages to the consumer,
music and film producers, and broadcasters, are obvious. This paper reports on a system
which offers excellent 5-2-5 codec performance, while preserving or improving the
balance, frontal perspective, and spaciousness of standard stereo recordings. The decoder
provides two or four independent rear outputs, which are capable of complete separation
from the other outputs for a single steered sound effect, and which preserve full left/right
separation during music. Decorrelated signals such as music can be panned forward and
back with full left/right separation. Frontal perspective and the balance between center
material such as dialog and vocals and other material is preserved through careful control
of the center channel level as a function of the center content of the input signal. This
paper will present a mathematical description of the matrix elements of the new decoder,
and discuss some of the psychoacoustic data on which it is based.
Introduction
Although initially developed for multichannel music reproduction, matrix systems have
been relegated to film sound. They are capable of much more. A preliminary design for a
new matrix topology has been tested by the IRT in Munich as a 5-2-5 codec, with
excellent results on a wide range of broadcast material. Although there were audible
differences, the differences were perceived as small changes in localization – and were
sometimes preferred to the original. We have extensively tested the new matrix with
ordinary stereo music material. In almost every case the multichannel matrix
reproduction of the material is preferable to a two-channel presentation. This is a
wonderful way to hear new sounds from your favorite recordings, and amazing sounds
from recordings which have been remixed for 5.1 channels. A high quality 5-2-5 matrix
offers a Rosetta stone for audio reproduction. A single inexpensive circuit can play both
encoded and unencoded music, films, and broadcast material. The advantage to the
consumer is obvious – high quality multichannel recordings available on compatible
CD’s, cassettes, videotapes, etc. The recordings can be played anywhere the consumer
has a player, and yet on a multichannel system true multichannel audio results. Who
wouldn’t want to hear multichannel broadcasts in an automobile?
Why do we need more than two loudspeakers? Research into the spatial acoustics of
small rooms shows that reproduction of stereo music through two speakers is not an
optimal solution, even when the listener is ideally situated. Additional loudspeakers,
driven with signals that provide audible spatial components, can significantly increase the
