Matrix (sound recording)

Matrix decoding is an audio technology where a finite number of discrete audio channels (e.g., 2) are decoded into a larger number of channels on play back (e.g., 5). The channels are generally, but not always, arranged for transmission or recording by an encoder, and decoded for playback by a decoder.

The function is to allow multichannel audio, such as quadraphonic sound or surround sound to be encoded in a stereo signal, and thus played back as stereo on stereo equipment, and as surround on surround equipment – this is "compatible" multichannel audio.

Matrix encoding does not allow one to encode several channels in fewer channels without losing information: one cannot fit 5 channels into 2 (or even 3 into 2) without losing information, as this loses dimensions: the decoded signals are not independent. The idea is rather to encode something that will both be an acceptable approximation of the surround sound when decoded, and acceptable (or even superior) stereo.

The notation for matrix encoding consists of the number of original discrete audio channels separated by a colon from the number of encoded and decoded channels. For example, four channels encoded into two discrete channels and decoded back to four-channels would be notated:

A simpler situation would be to derive extra channels from the existing ones, but with no special encoding at the origin. For example, five discrete channels decoded to six channels would be notated:

Many matrix decoders take advantage of the Haas effect, as well as audio cues inherent in the source channels.

The various encoding matrixes are described below.

Mostly used as a simple method for deriving back channels out of normal stereo recording (2:2:4), this matrix was also used for a specific encoding of 4 sound channels in some albums (4:2:4).

The first matrix system on the market, it was invented by Leonard Feldman and Jon Fixler, and sold by Electro-Voice. This matrix was used for specific encoding of 4 sound channels in many albums (4:2:4).

${\displaystyle j=+90^{\circ }}$ phase-shift, ${\displaystyle k=-90^{\circ }}$ phase-shift

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