Multichannel Matrix Surround Decoders for Two-Eared Listeners
David Griesinger · 1996
Although film matrix surround decoders are primarily four channel devices, with a single channel devoted to sound the sides and the rear, in practice there are almost always two or more surround speakers. These speakers are driven in parallel, with in some cases a delay modulation to “decorrelate ” the single surround channel. There is substantial interference between the various loudspeakers, resulting in a listener dependent comb filtering and a non-spacious surround. Although designs for decoders with more than one rear channel exist, these suffer from low separation between the rear channels when the decoder inputs are decorrelated- during music or effects like applause. Current decoders also suffer from various defects such as pumping of the music during dialog. This paper discusses a mathematical design for a matrix encoder and decoder with radically different properties- maximum lateral separation during music, accurate placement of directionally encoded material, and constant music level in the presence of any directionally encoded effect. Matrix equations for both a 5 channel and a 7 channel decoder are presented, along with an active and a passive encoder for 5 channel films. Comparitive listening tests show that the decoder reproduces standard films with substantially improved surround, and the combination of the encoder and the decoder reproduces 5 channel discrete films with little subjective loss.