Electronics project notes/Audio notes - multichannel and surround

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Earlier experiments

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Fantasound (cinema)

Disney's Fantasia (1940!) had a three-channel soundtrack (four tracks on the film; left, center, right, and the fourth controlling volume). There were other soundtracks from the time recorded in this way.

This was basically the first experiment, and it didn't take off in a big way (the film was not really a success), so not a lot of people heard it this way until much later re-releases.

Cinerama (cinema)

Cinerama is a wider concept, perhaps better known for having widescreen via multiple projections on a large curved screen (cf. Cinemascope, IMAX), but it also had seven channels of sound (five behind the screen, two rears)

https://en.wikipedia.org/wiki/Cinerama

Quadraphonic (frequently also pronounced quadrophonic?)

Quadraphonic comes from the 1950s, and became more widely and commercially known in the 1970s, if relatively briefly.

Quadraphonic comes in roughly three types:

• four separately stored channels

or, if you're Suzanne Ciani, presumably four separately generated channels(verify)

• four channels mixed into stereo in a separable way

which makes commercial sense in that you could sell one recording (particularly vinyl records, which can only sensibly go up to 2 channels) that everyone can play but some people can get more out of

there were multiple ways to do this, some better, some worse, all somewhat creative

• a way to add ambiance from regular stereo

which is subtler, but a nice addition that works on most any audio you feed it

There are also some fundamental acoustic flaws to positioning four speakers in a square.

https://en.wikipedia.org/wiki/Quadraphonic_sound

https://www.drdobbs.com/surround-sound/184406155

Split surround (cinema)

Further experiments in the 1970s, apparently used in at least Superman and Apocalypse Now, which seems to also be roughly the source of settling on 5.1 in terms of channels

Dolby glossary

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

For context

Dolby is a company

Dolby Surround tends to refer to multi-channel matrix schemes (initially analog, later digital)

Dolby Digital are digital codecs

Sometimes the channel stuff and the codec stuff is strongly related (or implied by context), so we generally don't need to be picky about terms, but knowing the distinctions can be useful.

Dolby Stereo (1976) seems to group both:

• Dolby SVA - A matrix decoding scheme,

from two channels on optical film

to four: left, right, center, and a mono rear surround

was used in cinemas, to give the option for encompassing sound based on existing film (avoiding separate multitrack and possible sync issues)

playable on regular stereo as-is, and consumer SVA decoders existed

soundtracks were sometimes SVA as a selling point, in that they were playable everywhere, but would would sound cooler on specific systems.

• Dolby Stereo 70mm - Noise reduction used on 6-channel magnetic tracks on 70mm film print.

...so not something any of us consumers would ever deal with

Dolby Surround (1982) is a marking used on players that used a simplified passive matrix decoder to play SVA(verify) into left, right, and surround (the center channel was fed equally from left and right, because that works out as phantom center)

(note: Dolby made things very confusing in 2014, see below)

Dolby Pro Logic (1987)

amounts to an expansion of what Dolby Surround does (still four channels)

implemented with ICs

does some gaining (and some frequency filtering?(verify)) depending on what's currently dominant, without changing total energy, which gives the perception of better separation (Dolby calls this 'steering')

Dolby Pro Logic II (2000)

takes regular stereo or Dolby Surround

produces five sensible full frequency channels (left front, center, right front, left rear, right rear).

Basically, the gaining/steering is better than before, meaning it adds a reasonable 'in the middle of the sound' feeling to most any stereo input

Dolby Pro Logic IIx (2003)

Can take regfular stereo, Dolby Surround, or 5.1.

similar, can output 6.1 or 7.1

Dolby Pro Logic IIz (2006)

similar, goes up to 9.1 height systems

Dolby Surround is, since 2014, used in a completely different meaning than before, basically referring to part of Dolby Atmos system.

https://en.wikipedia.org/wiki/Dolby_Pro_Logic#Dolby_Surround_(2014)

Dolby Digital, a.k.a. AC-3 is just about storing audio, not about processing it. [1]

Dolby Digital Plus (a.k.a. DD+, DDP. E-AC-3 (Enhanced AC-3), EC-3) is AC-3's successor, though it seems less known outside ATSC?(verify) [2]

DTS

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

DTS is a brand. When used to refer to digital audio, it typically refers to the DCA (DTS Coherent Acoustics) codec, as e.g. carried over SPDI/F.

DCA is a a compressed, digital surround format.

DTS Neo:6 is a similar idea to pro logic II: produces more channels from fewer.

DTS Neo:X is similar and goes up to 11.1 height systems