How do upmixers like Dolby Surround and DTS Neo/Neural work? They attempt to produce rear/center/vertical surround sound channels from a normal stereo source—and often seem to do quite a good job. Explanations I can find are all marketing mumbo-jumbo: “identifies spatial cues” 🤷♂️
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Dolby Surround is a matrix decoder (en.m.wikipedia.org/wiki/Matrix_de). The 2 channel audio stream contains 4 channels of signal that are combined with a phase shift and attenuation that makes it (mostly) usable in both stereo and surround playback environments.
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Where the original setup was wide-band, Neo uses a multi-band separation in combination with the matrix decoder. There’s further detail in the patent: patents.justia.com/patent/7003467
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Very interesting! This patent suggests that the stereo recordings are actually produced by the content creators in such a way to facilitate the “demixing” into 5 channels, i.e. by combining an originally-surround mix into a stereo mix. Are typical pop albums mastered this way?
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Correct. It is a lossy encoding technique to enable transport / distribution on media that does not support discrete channels. Non-encoded signals may ‘expand’ to a subjectively ok experience, but this likely differs to how it was originally created / mixed.
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Not my domain so I can’t comment on general popularity, but from personal experience usage within music distribution seems rare outside of remasters intended for surround listening.
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