Electronics project notes/Audio notes - multichannel and surround: Difference between revisions
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===Binarual and headphones are two extra cases we forget to think about=== | ===Binarual and headphones are two extra cases we forget to think about=== | ||
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'''Binaural audio''' usually refers to the fact our ears are like two microphones with a head-shaped thing inbetween. | '''Binaural audio''' usually refers to the fact our ears are like two microphones with a head-shaped thing inbetween. | ||
When | When we hear sound from our environment binaurally, | ||
it is almost unavoidable that the sound will arrives in both ears, | |||
with similar amplitude, and similar timing. | |||
When | When those timing differences are under a certain delay (see [[precedence effect]]), | ||
it becomes a significant part of how we localize sound -- or perceive it as reverb. | |||
Above that delay it is perceived as separate sounds. | |||
This is also why our home audio installations has more than one speaker - you can hear things beyond where that one speaker approximately is. | This is also why our home audio installations has more than one speaker - you can hear things beyond where that one speaker approximately is. | ||
To start with something a little more technical before more vaguer descriptions, | |||
the way you can mix towards two channels includes: | |||
: mono(-on-stereo, mostly giving a phantom center) | : mono(-on-stereo, mostly giving a phantom center) | ||
: LCR (hard panned channels) | : LCR (hard-panned channels - they do not appear in the other) | ||
: softer panned channels | : softer panned channels | ||
: stereo imaging | : stereo imaging (itself abused somewhat) | ||
: binaural | : binaural | ||
This is also where some confusion starts. | |||
The term 'stereo' has come such a generic term that it just means 'two channels', without saying how they are used, frankly any of the last four in that list. {{comment|(Arguably, 'stereophonic sound', being a technical-sounding term, refers to fewer in that list, but I wouldn't put bets on how other people use it)}} | |||
Also, if you compare those last four, | |||
: doing so on speakers will make them sound more similar, | |||
: while doing so on headphones makes them more clearly different | |||
This because headphones (arguably) do a very strange thing: | |||
they can produce sound in ''just'' one ear, that the other ear could barely hear at all. | |||
Doing so makes ''limited'' sense to our ears if we have a lifetime of two-eared practice, | |||
because even if it's right to our side, it still arrives in the other ear, maybe 20dB quieter, not a barely-perceivale maybe-80dB. | |||
--- | |||
So ''actually'', there are ''two'' variables here: | |||
the choices in mixing, as mentioned before: | |||
* mixing | * mixing | ||
:: mono | :: mono | ||
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:: binaural recording | :: binaural recording | ||
:: stereo imaging | :: stereo imaging | ||
combined with | |||
* sound emission and receiving | * sound emission and receiving | ||
:: speakers and binaural | :: speakers and binaural | ||
:: headphones on head | :: headphones on head | ||
...and, as audiophines will point out, with reverb in a room | |||
Say, you can capture binaural audio by, well, sticking two microphones on a head-shaped thing, | Say, you can capture binaural audio by, well, sticking two microphones on a head-shaped thing {{comment|(yes you can buy a research head for 10K, but 50 bucks of DIY will get you much of the way)}}, which will sound more natural in headphones. | ||
which will sound natural in headphones. | |||
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5.1 is left, center right, and two surrounds | 5.1 is left, center, right, and two surrounds | ||
: common due to use in early Dolby and DTS | : common due to use in early Dolby and DTS | ||
: a bunch of newer media has stereo and 5.1 | |||
: note that 5.1 systems are technically often set up incorrectly - the surround speakers should be beside you, not behind you, though there are not a lot of cases where this ''really'' matters, for the 'enveloped in sound' feel it's good enough, and it may be more practical for room layout | |||
The .1 is the subwoofer | |||
: .2 means two subwoofers, which seems... redundant. | |||
7.1 has a left-rear and right-rear | 6.1 adds a single center rear to 5.1 | ||
7.1 has both a surround-left-and-right and a left-rear and right-rear; i.e. one set more to the side, one to the rear | |||
: less common to find audio streams pre-mixed in 7.1 | |||
There's also 9.1, 8.2, 9.2, 11.2 | There's also 9.1, 8.2, 9.2, 11.2 | ||
8 is like 7 | 8.something is like 7.something plus a rear center | ||
9.something is like 7.something plus front-wide between fronts and surrounds at the side | |||
11 is somewhat like 5.1 plus four 'presence' speakers in the corner. | 11 is somewhat like 5.1 plus four 'presence' speakers in the corner. | ||
: auro 11.1 is more like 5.1 plus another 5 above against the first 5, and one on the ceiling | : auro 11.1 is more like 5.1 plus another 5 above against the first 5, and one on the ceiling | ||
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DTS uses higher bitrates than AC3, AC3 is more widely supported | DTS uses higher bitrates than AC3, | ||
AC3 is more widely supported | |||
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:: ES Discrete | :: ES Discrete | ||
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SPDI/F, while it carries surround, carries compressed surround (AC3 or DTS), though now that people know of the lossless and tend to use HDMI on home systems, SPDI/F | SPDI/F, while it carries surround, carries compressed surround (AC3 or DTS), though now that people know of the lossless and tend to use HDMI on home systems, SPDI/F may be slowly on its way out. | ||
--> | --> | ||
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These use the [https://en.wikipedia.org/wiki/Head-related_transfer_function head-related transfer function] (basically, knowledge of how head, ears, and brain cooperate to localize sound) to create a specific 3d sound field on systems with just two speakers. | These use the [https://en.wikipedia.org/wiki/Head-related_transfer_function head-related transfer function] (basically, knowledge of how head, ears, and brain cooperate to localize sound) to create a specific 3d sound field on systems with just two speakers. | ||
This is on-the-fly processing. | |||
They don't invent placement of sources, they just make you feel a little more immersed than. | |||
How well that works does depend on the audio on the inside as well. | |||
There are a few implementations. | |||
Frankly, the surround-ness of any of these is a gliding scale. | Frankly, the surround-ness of any of these is a gliding scale. | ||
Yes, Dolby and DTS invent useful channels for sound not really mixed for them, | Yes, Dolby and DTS invent useful channels for sound not really mixed for them, | ||
which is nice because sound comes from all directions, not because it's accurate to anything. | which is nice because sound comes from all directions, not because it's accurate to anything. | ||
--> | --> | ||
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You may have seen things like SRS Wow in some music players | You may have seen things like ''SRS Wow'' in some music players | ||
SRS Wow is branding that groups three parts: | SRS Wow is branding that groups three parts: | ||
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: Focus - intended to make car sound | : Focus - intended to make car sound | ||
: TruBass - tricks you into thinking there is bass that tiny speakers cannot actually produce | : TruBass - tricks you into thinking there is bass that tiny speakers cannot actually produce | ||
SRS Wow HD - adds high frequency contouring | SRS Wow HD - adds high frequency contouring |
Latest revision as of 18:13, 13 May 2024
Why
Binarual and headphones are two extra cases we forget to think about
Earlier experiments
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
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
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