This is topic (?)Theatre Sound Formats For Dummies(?) in forum Film-Yak at Film-Tech Forum ARCHIVE.


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Posted by Nate Lehrke (Member # 1460) on 04-04-2003, 03:01 AM:
 
I am looking to be treated like moron for this question, meaning, don’t assume that I know anything about this. Any other threads I can read to get info?

Can someone give me a crash course in sound formats/systems?

What are?
Mono
Stereo
DTS
SDDS
Digital
Dolby Digital

What are the differences or what is the order in quality?
What other formats are being used in theatres?
Do these names have any other aliases?
 

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Posted by Michael Schaffer (Member # 1204) on 04-04-2003, 04:43 AM:
 
Click here
 

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Posted by Michael Brown (Member # 890) on 04-04-2003, 08:00 AM:
 
Mono -One channel analog sound

Stereo - two (or more) channels analog sound. This can also refer to Dolby Stereo with is a 4 channel analog surround sound system.

DTS - 6 Channel digital sound, sound is held on a CD, a timecode on the films keeps it in sync.

SDDS - 6 or 8 channel digital sound. Sound is recorded on both edges of the film.

Digital - (see DTS, SDDS, Dolby Digital)

Dolby Digital (SRD) - 6 channel Digital Sound. Sound is recorded in-between the sprocket holes on one side of the film.

In terms of the order in quality. This is debatable.

For me its:
DTS, Dolby Digital, SDDS
 

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Posted by John Lasher (Member # 968) on 04-04-2003, 10:19 PM:
 
Ok. I'm going to pretend to be an idiot. (pretend? )

[idiot mode]

quote:

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analog

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digital

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timecode

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what's a timecode? that sounds like some sort of rule about how long the movie can be.

[/idiot mode] (are you sure about that, John?) [/multiple personality mode]
 

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Posted by Jeffry L. Johnson (Member # 453) on 04-05-2003, 08:05 AM:
 
Film Sound History Timeline
Motion Picture Sound - Part 1
American Widescreen Museum - The History of Motion Picture Sound
Elmer's Guide to Motion Picture Sound Formats
 

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Posted by Evans A Criswell (Member # 381) on 04-05-2003, 09:38 AM:
 
A Brief Explanation of Film Sound that I wrote for hsvmovies.com long ago.

analog = data represented by continuously variable physical qualities (like strength of magnetic field left on tape after head passes over, or spacing between gaps on a Laserdisc).

digital = data represented by numerical digits (sequence of zeros and ones, as on a CD, or a sequence of discrete quantities using any representation which may be reproduced exactly without loss).

However, the terms are sometimes misused. Digital data can be stored in analog form on media (such as tape or laserdisc media (Look at how Dolby Digital is stored on the analog soundtrack!)) Some analog devices are referred to as digital devices if they contain digital frame buffers. Most "Digital TVs" beig sold take analog inputs, redigitize the signals, and do digital processing on them before displaying them on CRTs by sending the CRTs an analog signal.
 

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Posted by John Lasher (Member # 968) on 04-05-2003, 11:27 PM:
 
This is the description I've given to a few people who've looked at me sideways upon hearing the term:

The DTS timecode on a film print is basically a really long barcode that tells a computer (more or less) which part of the movie is showing on the screen, the computer plays the corresponding part of the soundtrack from a CD-Rom.
 

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Posted by Manny Knowles (Member # 1171) on 04-06-2003, 01:05 AM:
 
i would argue that dts timecode is actually many barcodes in succession and not one long one.

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as for a working definition of the formats (for dummies) i offer the following:

first we need to establish the terms "track" and "channel." [note: see also michael schaffer's definition below.]

a track is an actual individual recording. a cassette audio tape contains two tracks -- one for the left channel, the other for the right channel.

a channel is a path to a loudspeaker -- or to an array of loudspeakers. in the cassette tape example, the left channel is driven by the left track on the compact disc but the terms are not necessarily mutually exclusive, as we shall soon see.

mono -- one channel of sound. this can be driven by a single track or else by two identical tracks (see matrix decoding, below)

stereo -- anyone with normal hearing listens in stereo. most stereo applications employ only two channels of sound -- one for each ear. this usually works fine when listening takes place at close range but in large venues like a cinema, the stereo effect is greatly enhanced when the playback systtem employs more channels. cinema stereo typically utilizes channels designated by their location in the room. the speakers behind the screen are known as left, centre and right. the speakers above the seating area are for the surround channels. analog surround is mono. digital audio provides stereo surround channels (left surround, right surround). a newer system (see below) introduced a third surround channel (back surround).

the center (screen) channel is important because it almost always carries the dialogue track. isolating the dialogue and placing it in the centre of the screen improves intelligibility of the spoken words.

to understand how these multitrack systems work, we need to introduce two more terms -- "matrix" and "discrete."

matrix -- analog cinema stereo uses two tracks (known as Left-Total and Right-Total, or Lt and Rt). these two tracks are constantly analyzed during playback. sounds that are common to both tracks are isolated and redirected to the centre channel loudspeaker. so in the case of bilateral mono tracks (i.e. two identical tracks side-by-side) all of the information gets routed to the centre channel. sounds that are common to both tracks, but recorded out-of-phase, are also isolated and redirected to the surround channel (mono). the remaining sounds pass through to the left and right channels behind the screen. this illustrates why "track" and "channel" do not always mean the same thing.

discrete -- digital systems use discrete tracks. this means that for each channel, there is an actual track. in this case, the terms "track" and "channel" are interchangeable.

subwoofer -- a subwoofer is a speaker system that is designed to reproduce very low frequencies, which are typically felt moreso than they are heard. a device known as a "crossover" can strip away all low frequencies and redirect them to the subwoofer channel. not only does this ensure that those frequencies get properly utilized, it also protects the main loudspeakers which could sustain damage if exposed to these frequencies.

some systems also employ additional channels behind the screen....

left-extra appears between centre and left channels
right-extra appears between centre and right channels

why the extra channels? there are two good reasons. larger screens really benefit from having these channels. first, they fill in what would otherwise be two gaping "holes" between centre and the two outer channels (left and right). second, they give mixers the option to separate the music track from the effects track, the idea being that the reduced "competition" between sounds coming out of any given channel will improve intelligibility.

benefits of digital audio

-- discrete channnels eliminate matrix-decoding errors. crystal clear audio over long-term (versus gradual degradation of analog tracks).

-- improved dynamic range means that digital sound can be quieter than an analog track (which will always contain some "noise") and digital tracks can get louder than analog (the analog waveforms must fit within a space that imposes this limit).

-- improved frequency response (lower lows, higher highs)

digital sound formats in use today --

dts -- this is a dual system, which means that there are two components. the first component is the film itself which does not carry the digital audio but instead carries a timecode track. timecode essentially lets us know how far we are into the movie (which movie, which reel, which minute, second and frame). the second component is a cd-rom (or pair of cd-roms) which contain the digital audio data. a special player interprets the timecode and plays the correct part of the disc(s).

advantages of dts -- placing the sound on the disc(s) means that the audio does not need to be as compressed as the other formats (see below). additionally, the actual tracks are spared from the wear-and-tear of projection. the timecode itself is located between the image area and the soundtrack. thus, dts timecode is least likely to sustain wear-and-tear damage. dts timecode can also be used to trigger text display devices for the hearing impaired. different discs can be used to allow for multilingual presentations with the same film print. similiarly, discs can also contain descriptive narration for the blind. conceivably, the timecode could also trigger automation cues one day. dts has the simplest threading path and does not cost as much as the other systems.

disadvantages of dts -- often the discs do not arrive with movies. also, the projectionist must always be mindful to move the discs if the print is moved.

dolby sr-d -- this is a sound-on-film format which, of course, means that all of the audio information is printed right on the film. the data is stored in between sprocket holes.

benefits of sr-d -- sound-on-film format means that when the print arrives, so does the sound. from a marketing perspective dolby is the most recognized brand name of the three digital cinema systems in use today. also from a marketing perspective, dolby continues to produce a new promo trailer on a more regular basis than the other companies.

disadvantages -- dolby has a more complicated threading path and costs about twice as much as dts to install. the location of the data in between the sprocket holes puts the data in a less-than-ideal place. due to the limited space, dolby digital data is also more heavily compressed than dts. it should be noted, however, that most people do not perceive a difference between the quality of dolby digital and dts audio.

sdds -- this is sony's system. the data is stored on the outermost edges of the film print.

advantages of sdds -- sdds is a sound-on-film format and it is the only digital system that has a digital backup; the others use the analog mix as the immediate backup. sdds is currently the only digital system that offers the extra screen channels (for a total of 8 channels of sound).

disadvantages of sdds -- people with sensitive hearing complain that sdds has a more "screechy" quality than the other 2 formats. the location of the data at the extreme edges of the film is unfortunate in terms of potential for damage. sdds reportedly "drops out" frequently and, despited the digital backup, will often default to the analog mix. despite its being the least reliable and the least known brand, sdds has always been the most expensive system to install. very few movies take advantage of the 8-channel option. few theatres are configured for 8-channel playback.

[ 04-06-2003, 08:07 AM: Message edited by: Manny Knowles ]
 

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Posted by Daryl C. W. O'Shea (Member # 1303) on 04-06-2003, 01:32 AM:
 
Since barcodes are really read all at once, whereas DTS timecode isn't, I would say that printed DTS timecode is really an optical serial bitstream.
 

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Posted by Manny Knowles (Member # 1171) on 04-06-2003, 03:07 AM:
 
daryl -- you go, boy!

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i'd also like to mention the concept of noise-reduction (or "nr")...

dolby a
dolby sr

both of these formats are matrix-decoding systems combined with noise-reduction processes.

"noise" is unwanted or disorganized sound. analog tracks are incapable of reproducing total silence. the sound of silence is more like a 'hiss' sound. during the mixing process, several layers of sound are combined and the inherent noise on all those tracks can build up and play havoc with the real sounds, especially during quieter passages.

dolby's noise reduction systems are capable of analyzing soundtracks and 'weeding out' unwanted noise while preserving everything else that the director wants us to hear.

dolby sr ("spectral recording") is an improvement over the performance of dolby-a, offering greater frequency response.
 

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Posted by Michael Schaffer (Member # 1204) on 04-06-2003, 07:50 AM:
 
I really hate to disagree with Manny, but I have to in the case of his definitions of channel and track. The channel is the complete path a signal takes, and the track is the physical recording of the channel(s). A CD has only ONE track as it is a serial data stream which is read from the CD, and this one track contains TWO channels which are interwoven with each other.

Evans said that Dolby Digital track was stored on the analogue soundtrack. That is not correct, the DD soundtrack is there digitally, in optical form. The same applies to the storage of digital signals on a magnetic tape. It still is a digital storage technique, even though the tape is an originally analogue medium. The difference between A and D is not the medium, but the principle according to which the data are stored. If you take a piece of paper and write down information using a code of long and short dashes or two different symbols, that is a digital recording too.
I am not sure I understand what he meant with analogue spacing between gaps on a Laserdisc. The Laserdisc is a purely digital format, or have I missed something here? I am not very familiar with that format.
If you look at a picture of a CD track, you can also see there are long and short "pits" and "lands". Oddly the pits rise above the lands. That is because the pits are pressed into the CD from the other (label) side. Most people tend to think that the pits are 0s and the lands are 1s, but it is actually the transition from pit to land (the edge of the raised structures) or back which is the 1 value and the space between edges, be it on pit or land, is a longer or shorter series of 0s.

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People with sensitive hearing complain that sdds has a more "screechy" quality than the other 2 formats.

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Evans said that Dolby Digital track was stored on the analogue soundtrack. That is not correct, the DD soundtrack is there digitally, in optical form.

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The Laserdisc is a purely digital format, or have I missed something here?

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Laserdisc is an analog medium. Yes, there are pits, but the spacing between the pits determines the signal reproduced. It's frequency modulated. High frequences = closer pit spacing. It's not digital. Laserdiscs originally contained analog composite video with stereo analog audio. Later, 2 PCM audio tracks were added. When DTS is put on Laserdisc, it's stored on the 2 PCM tracks (just like on DTS CDs). The Dolby Digital, if present, is stored on one of the analog stereo audio channels (left or right I can't remember which). However, all of this digital data is stored in analog form on the disc!
 

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Posted by Manny Knowles (Member # 1171) on 04-07-2003, 03:56 AM:
 
Isn't this supposed to be "for dummies" ?

I vote for a new thread to explore the finer points, especially if it's gonna take us into the realm of video...and THAT should happen in "The Afterlife" forum, don't you think?
 

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Posted by Michael Schaffer (Member # 1204) on 04-07-2003, 06:12 AM:
 
Thanks for the info, Evans. How does the spacing determine the signal? What is the diffeence between Laserdisc and CD in the way the signal is stored and read?
 

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Posted by Lionel Fouillen (Member # 1475) on 04-07-2003, 06:27 AM:
 
About screechy sound and noise reduction.

Some people complain about such "screechy sound" not only with some SDDS projections but with other digital systems as well. The problem, I think, comes with sound mixers unappropriately using the full "window" of digital sound, that is a 90dB signal-to-noise ratio across a full 20Hz-20kHz frequency range. This "window" exceeds the limits of the average human auditory window, the latter being much less tolerant on the high-freq range. Hence, if recorded at too high sound pressure levels (dB), some high-pitched sound effects will appear painful to the human ear.
 

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Posted by Evans A Criswell (Member # 381) on 04-07-2003, 07:37 PM:
 
No, let's not move the finer points to the afterlife yet. I provided my example, not to get into video formats, but to illustrate that digital data can be stored as analog. If someone wanted to use the normal optical soundtrack on film to store digital audio, and install a special apparatus to read and decode it, then they could do it. The digital sound could be converted to a wave form, then read by a normal sound head, and the sound output could be hooked to a device to decode the digital data. I don't know how much bandwidth one could get by doing that, but clearly a good bit of digital data could be encoded on film that way along with the image if one wanted to.

In a different light: Think of how much digital data could be put on 35mm film if the entire silent aperture were used!
 

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Posted by Joe Redifer (Member # 3) on 04-07-2003, 07:46 PM:
 
How much digital info (in MB) does the sound from Dolby Digital and SDDS combined take up on a two hour movie? I wonder if you could use film prints to pirate digital data? There could be one special print encoded by an evil person at the labs to have, say, and MPEG version of the print it is shipped on sent to a special theater with an evil projectionist. The SDDS and Dolby Digital hardware could not decode the data as sound, of course. There would be super-special hardware to decode the data from the SRD and SDDS tracks back into the pirated MPEG (or maybe Adobe Photoshop or a bunch of Metallica MP3s or something). It would be worth the hundreds and thousands of dollars it would cost.
 

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Posted by Christopher Seo (Member # 7) on 04-08-2003, 02:36 AM:
 
Regarding "track" and "channel":
Fortunately, I have been able to reconcile Michael's and Manny's definitions of "track" and "channel". Both are correct, but we must clarify a semantic distinction when speaking about digital sound. With analog sound, Manny's original definitions hold with no further elaboration: a discrete channel of analog sound requires a physically discrete track, i.e., one recorded physically separate of the others. However, the nature of digital data inherently requires reconstitution of the sound (or any) information into analog form for ultimate perception by humans, and as such, the data representing discrete channels of sound can be in any physical format-- intertwined, as it were. In fact it is advantageous to do so for error correction purposes (e.g. SRD, and I'd assume SDDS).

In this sense, the analog notion of "track" evolves, taking on more of an abstract meaning. A "track" of sound is not simply a physically separate sound recording, as in the visually obvious case of optical Lt and Rt; it is a conceptually discrete delivery path for sound, as intended by the mixers, which the digital circuitry is programmed to reconstitute individually and separately, as if no other sound paths existed. In other words, we should distinguish "soundtrack" from "track". A "soundtrack" is the physical total of the recordings which constitute a whole, and a "track" is a discrete sound path which can be read off a soundtrack.

Evans:
I don't understand what you mean by your idea. Are you suggesting that a digital soundtrack could be put into the optical analog soundtrack area in addition to the analog track, or in place of the analog track?

Regarding SDDS sounding "screechy":
There was a FHF discussion on the hf deficiency of SDDS pink noise here.
 

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Posted by Michael Schaffer (Member # 1204) on 04-08-2003, 05:54 AM:
 
The SDDS pink noise is not "deficient". It is just right for alignment of the sound hardware which has a better high frequency defintion. If done right, an SDDS systems sound clearer and crisper than some other formats which have a more diffuse high frequency playback playback perceived as "softer".

Interesting defintions found here.

channel: 1. A connection between initiating and terminating nodes of a circuit. 2. A single path provided by a transmission medium via either (a) physical separation, such as by multipair cable or (b) electrical separation, such as by frequency- or time-division multiplexing. 3. A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths. 4. Used in conjunction with a predetermined letter, number, or codeword to reference a specific radio frequency. 5. The portion of a storage medium, such as a track or a band, that is accessible to a given reading or writing station or head. 6. In a communications system, the part that connects a data source to a data sink.

track: On a data medium, a path associated with a single read/write head position as data move past the head.

digital: Characterized by discrete states.

analog data: Data represented by a physical quantity that is considered to be continuously variable and has a magnitude directly proportional to the data or to a suitable function of the data.

Evans was right about the Laserdisc.
 

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Posted by Evans A Criswell (Member # 381) on 04-08-2003, 03:27 PM:
 

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Evans:
I don't understand what you mean by your idea. Are you suggesting that a digital soundtrack could be put into the optical analog soundtrack area in addition to the analog track, or in place of the analog track?

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