HELP!
Thanx!
Andrew McCrea

P.S. The theatre will begin construction soon. The theatre is slated for a July 20, 2001 opening! I heard that THX has to have special auditorium layouts and I hope our blueprint proto-type can be changed for THX certifications if we choose it!

As for which Digital system to choose, they each have their good and bad points.

SR-D (Dolby Digital) is placed on about 99.9% of release prints today. In my opinion, it has excellent sound in the lower ranges (bass for explosions and such). Problems with it include tricky alignment (it's printed between the sprocket holes so the little "camera" has to be timed just right), a somewhat high compression rate and the fact that the track is somewhat easily damaged because of its placement on the film.

SDDS (Sony Dynamic Digital Sound) appears on about 98% of realease prints, gives you 8 track capability (Left and Right Extra between the L / R and Center channels) and has the lowest compression rate. It also, in my opinion, has the best channel seperation (you can easily tell where the sound is coming from). Trouble with it is because it is printed on the very edge of the film (both edges) it is easily damaged. When damage occurs to any of the 8 low compression tracks, the system falls back to a back-up track that contains all 8 tracks at extremely high compression (sounds worse than analog!). This will happen even with brand new from the lab prints. Also, SDDS units are notoriously trouble prone and will fail a lot.

DTS (Digital Theatre Systems) has CD Rom discs which contain the sound so film damage will not affect the sound quality. It appears on about 98% of release prints today and uses the same compression ratio as SR-D. It has, in my opinion, the best seperation between screen and surround channels which will really give you that "being in the scene" feeling. Problems with DTS include the fact that the sound doesn't automatically go with the print (you have to remember to move the discs too and some prints will not have the discs returned with them so you must order new) and their older CD Rom drives are notorious for freezing up and not wanting to read properly.

I hope all this info helps. I can't tell you which system to choose because it really depends on your preference and needs. Good luck!!

-Mike
 

-Mike
 

I don't believe this to be the case: DTS uses approximately 3:1 compression whereas Dolby Digital is compressed between 10:1 and 12:1.

Could someone verify this?
 

For example, THX auditorium are designed to be very quiet. To keep outside noises as low as possible, one thing they will specify is that any AC compressors be mounted over the booth area rather than the auditoriums. The compressors may be mounted using vibration-isolation mounts; the exact type of isolation mount must be calculated by someone, based on the size and weight of the compressor (so you can't just go out and buy any mount.) They also usually specify the the HVAC ducts be internally padded/insulated. They may require that the ducts zig-zag once to reduce patrons hearing the fan noise.

So if a theater hard-mounts AC compressors directly over the auditorium using a very short, uninsulated duct, it could be very expensive to change later.

Go to the Manuals section here, and download the document; "THX Architectural Suggestions" for some idea of what involved.

When our theaters were THX approved 6 years ago, it cost $10,000 per auditorium ($1,000 a year after the first.) That price changes depending on how many auditoriums you want to do at one time, if they are all the same basic, "standard" design, etc.

I think if I were pressed for money, I would buy digital sound equipment and contact a person who has done THX auditoriums before and ask them to help with the design. It might not be perfect, but you would avoid several pitfalls if you do it yourself, and perhaps try for THX at a later date.

Best Tech Support: DTS. No contest.
Most Maitenance Free: DTS from my experiences. SRD is also very good, though.
Easiest format to work with: SRD. Thread it up and your done. Virtually everything is in SRD.
Cheapest as by MSRP: DTS. Followed by SRD and then SDDS.
Best Channel Seperation: DTS followed very closely by SDDS. I find SRD to be "acceptable".
Best sound: DTS then SRD then SDDS in my opinion. SRD ranking that high is quite interesting considering that it has about 3 times the compression as SDDS does.
My suggestion: CP 650 with a DTS 6D deck and an EX decoder. Will give you SRD-EX, SRD, DTS and DTS-ES.

I disagree. While DTS does an excellent job of telephone and Internet tech support(Karen RULES!), I have to say that in my experiences, Dolby has far superior support... As always YMMV...

Aaron

 

I no longer push DTS for my installations anymore because of this incident. Dolby equipment rarely ever gives me any grief and their tech support as well as their products are fantastic.
 

Rory
 

It's just that Dolby seems to do everything required- and then go one step more.
 

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I love to smoke I smoke seventhousand packs a day and I'm never F*&ing quittin!-- Denis Leary
 

"the system has the capability of up to 8 discrete tracks and uses a 5:1 compression technique (probably based on that of the mini-disk from Sony) and the writing algorithm maintains 100% data redundancy so enabling quite large flaws in the print to be survived."
 

You may be right about the frequency of SDDS tracks showing up on prints decreasing. I can't really give you exact numbers, obviously, I was just relating my own experiences over the past few years. You are, of course, correct about SR-D showing up most often!

Isn't that 30:1 compression ratio on SDDS only for the secondary / back-up digital track Gordon? Or am I just not understanding something here?

-Mike
 

It is not the "amount" of compression that is relevant anyway, but how it is used. The real issue is that DTS uses a system (called APTX) in which the data is fully recovered (well, 99%), and is fully intact - unaltered from the orginal. There are virtually no losses and the audio is equivalent to CD audio.

However Dolby (and to a lesser extent, SDDS) use systems based on Dolby's AC3 compression scheme which discard (forever!) large amounts of audio data, particularly when all 5.1 channels are carrying lots of information at the same time. These systems use what Dolby refers to as "psycho-acoustic masking" which is a method of data compression supposedly modelled on the human ear, and it's tendancy to not hear certain quite sounds in the presence of other much louder sounds. So the quite stuff (that you're not supposed to be able to hear) is just thrown away. The more channels that are working at the same time, the more audio that is discarded.

However anyone with a half way decent working set of ears would have to conclude after listening to any SRD track that the human ear that AC3 is modelled on was probably in excess of 70 years old!

SRD does sound quite acceptable when only the centre channel is working, but add stereo music and effects in the surrounds at the same time and the whole thing starts to really come apart. Anyone disgree - (all of those deaf heads out there need not reply).

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The big mistake that the THX people make is placing their four analyser microphones all over the damn shop. They try to create an average response in very last nook and cranny of the auditorium, and the fact is you just can't do it, and this method just creates more problems than it solves.

We have found over and over, that placing the four micphones in a tilted diamond pattern which is restricted to the main seating area (two thirds back where most people sit) works every time and produces accurate highly repeatable results. You go back in six months and set up the mics again and the response is almost identical.

And the sound is smooth and natural, because you are not pushing the capabilities of the equalisers in a vain attempt to make every part of the auditoruim sound perfect.

 

with AC 3 I do agree. It is just one track carrying about 256 kB of sound information per second. This would equal roundabout 4 telephone calls with 300 - 3k Hz single octave 8 bit sound. No way 6 (5.1) fullrate channels - the limitation is obvious. Spectral (lacking bodily substance, imaginative, fake, illusory according to Webster) tricks work quite well, but once you are aware of the tricks, it sounds boaring. Basicly it is monophonic sound split to 5.1 channels.
SDDS uses about 2 MB data per side, and feeds 12 discrete fullrange channels, whereas AC3 uses bit bucketing (shared as requested by signal) data. Normally synphonic music present on most mixes is lost during loud action sequences, the psycho acoustic masking is really not everyones treat. Theoreticly SDDS would be better, but to archive higher capability, you need to undergo carefull mixing and mastering, which is rarely the case. The request of exhibitors worldwiude, going for new multicomplexes, for more movies a week (All movies must be changed after 3 weeks or so), lead to lower quality films, with less production time and care for the single product.
The ATPX 100 used on DTS could nearly create the raw data, but unfortunately uses linear prediction in the theatrical variant, which could lead to audible errors, if not carefully mastered.
Both home systems, AC3 and DTS are better, they have higher data rate, and use more advanced decoding algorythms then their theatrical counterparts.
SDDS is known as a theatrical system only.
 

your description of Dolby Digital sound rather strange to me.
When listing to good mixes like Matrix or Fight Club in good sounding cinemas, I have not all the feeling of "monophonic sound splitted to 5.1". Or did I miss something of your points.
In fact I have no real problems with Dolby Digital sound quality of these movies. This at least is true for the original version. The German dubbed versions have inferior sound quality as usual.

For clarification of the discussion in this tread: Here are the parameters for the digital film formats, given in the sequence Dolby Digital / DTS / SDDS.

Resolution: 18 / 16 / 18 Bit.
Sample Rate: 48 / 44.1 / 44.1 kHz.
Data reduction: 13.5:1 / 4:1 / 5:1.

Discrete recorded channels:
Dolby: 5.1
DTS: 5.0, the subwoofer is recorded in the surround channels LS, RS with Xover at 80 Hz
SDDS: 12.0, subwoofer is fullrange. There are 4 failsafe channels C, SW, Mix of L+LC+LS, Mix of R+RC+RS.

Data Rate: 320 / about 880 / about 1900 kBit/s.
(for DTS and SDDS the data rate is calculated from the other data as I did not find a specification).

For SDDS we should consider that usual 5.1 mixes only uses 5.05/12 of the data rate (=about 800 kBit/s, the subwoofer only requires 1/200 of the bandwith).
So the data rate for SDDS is not so impressiv anymore.

Physical formats on the print:

Dolby Digital
Size of a bit: 33 um (micro meter).
78 bits by 78 bits between each perforation, giving
Physical data rate: 584 kBit/s, the difference to the data rate 320 kBit/s is used for syncs and error correction

SDDS
Size of a bit: 24 um
Physical data rate: there we have a mystery.
On one side I found the spec 4000 kBit/s.
On the other side I found the specification that 64 bits minus 6 for snyc are traveling on each side of the film. This calculates to a total of about 2200 kBit/s.
Where are the other bits stored?

The smaller size of the bits might be an other reason for earlier wearing out of SDDS tracks.

Data reduction of 3 digital formats is not lossless. So it is important to know/hear the defects during the mix as (it is necessary for matrixed analogue mixes).
Dolby: the DS10 encoder is provided to the mixing studio, so the studio has control over the encoded/decoded sound.
DTS: external encoding, the DTS-Tower provided to the studio deals with the different record format (subwoofer in the surround channels).
SDDS: external encoding

Additional to home formats:
Dolby also uses AC3 but with higher data rates. Of course I would prefer to have higher rates for film as well.
DTS uses a complete different codec and different record channel layout for home applications.
 

After playing, a rep from Dolby gave a short talk/QA session about AC3. He made a specific point to say that; Dolby, Inc. was *not* saying AC3 was the best at everything.

He said that Dolby's offical position is that; AC3 is the best sounding process using only 256kb/s. Dolby acknowledges there are better compression algorithms. However, bandwidth is limited in most applications- there's only so much room on a DVD, HDTV signal, modem, or space between sprocket holes. Dolby wanted *one* process that would work for all these applications.

If you've ever done any network administration, or worked on engineering projects requiring "real-time" analysis, etc. you quickly see that there is always a struggle for bandwidth.

So, while not perfect, I think AC3 was a "real-world" solution that does quite well for the task(s) it was designed for.

Besides, I don't feel that super-high-quality audio is obtainable in a theater auditorium.

I think that the highest compressed soundtrack (AC3) still has more quality than the sound system's ablility to play back. The reasons are; the speakers and the acoustics.

Speakers for theaters need to be designed to "fill" a large area, and auditorium acoustics are difficult to control (unlike a home system where the smaller speakers can be made for more accurate reproduction, and the room acoustics will not change significantly after EQ'ing.)

Look at what happens in a theater; after putting up the speakers, we put a "low-pass filter" (the screen) in front of them. Then, we EQ an empty auditorium, even though it can get filled with people. To cover the widest area, some seats usually need to be "left out" of the HF speaker's coverage area, resulting in those patrons hearing poor HF quality.

So, my point is that the speakers and acoustics will degrade the audio signal enough such that (I feel) compression rates do not matter. Let's start working on picture quality.

------------------
I love to smoke I smoke seventhousand packs a day and I'm never F*&ing quittin!-- Denis Leary
 

just to clarify. The SDDS System, according to the SDDS Recorder System's product information manual states the following data:

Sample frequency 44.1 kHZ (could adopt any other rate by high quality sample rate converter)
Dynamic range 90 dB
Number of channels 8
Compression rate 1:5 (ATRAC 100)
Recording bit rate 4 Mbit per second
The system is discrete 12 full range channels (8 + 4 backup), which in return will deliver around 333 kbps per channel.

It's rate per channel is higher than AC3's shared 256 kbps used for 5.1 channels in a bit bucketing technology.
This is why I tend to state as a "shared mono system".
The compression rate in practise is somewhat 4.5 :1 and is identical with ATPX 100's. DTS states 4:1, whereas SDDS states 5:1, whatever mathmatical rounding is applied.
AC3 could also be 15.8 : 1 with very saturated mixes.
We also have to keep in mind, the versions of the compression systems on all formats are rather 'old', as the date back to about 1990, in microelectronic timeschedules, and that some consumer product versions rely on more advanced algorithms. Correct, DTS is totally different, and no prediction is used.

Both systems on film (SRD and SDDS) rely on derivates of the Dolby proprietory BCIRC (Block cross interleave Reed-Solomon) error correction algorithm.

Which tracks wear first, I do only know DTS stays longest, but also 1200 runs on SDDS are not only officially archieved, I have proof it does still work.
On the other hand I have had SRD prints run 30 times on a Kinotone with the old type gates, and they were unreadable...
SDDS uses a specific technology with indirect light, which keeps effects from scratching minimized. Direct light, as used with CAT 700 would have severe shadow effects, making readout difficult. On the other hand Dolby Digital has larger dots. There are many factors, starting with careful printing. If the dots are printed sharp, the print will be more vulnerable than contrasty printed tracks. High speed printing does certainly not assist reliability, but does it really matter, as most films nowadays have just limited run of 2 - 3 weeks at the maximum, which would stay within even worst case limits of allowable runs.
That's the theoretical side. How good (or bad) something finally sounds is dependent on many other factors, starting from the care taken during mixing and printmastering, and ending with theatre acoustics and B chain design.
And we should aim our goal on presenting films the best possible way - which is simply care taking in exhibition, and interest in one's job.
 

the problem with the Sony SDDS document is that it is not consistent.
I did not find the defintion of "recording bit rate".

1. Is it the net bit rate of the data stream as you assume?
Each channel would use 333 kBit/s as you calculated.
The compression rate would be 2.4:1 as the data rate of the uncompressed input data is 794 kBit/s.
This is in contradiction to the rate of 5:1 specified by Sony. This compression rate calculates to a bit rate of about 1900 kBit/s for all 12 channels.

2. Is it the physical data rate on the film?
When you look at the figure "Data Block Specification (Release Print)" in the document, you will find the physical parameters given in my post. This calculates to some 2200 kBit/s total recorded on the print.
Is there an additional data reduction I did not see?

Dolby Digital: The data rate 320 kBit/s of the AC3 data stream for film was specified by Dolby people. Tom Holman also gives this data rate in various publications e.g. in "5.1 Surround Sound Up and Running".
The common bit pool is no disadvantage to me as it makes best use of the limited bandwith.

I agree that the digital format for the A-chain is not everthing.
As John mentioned the acoustics and B-chain is more important for getting good results.

 

I bet you-all out there didn't know any of this stuff.

 

One test, which someone might conduct. Play Pink Noise in all formats over a good B chain (please, no 2 way systems in 450 seat theatres), correctly designed.
And I would be curious about the results.
Which Pink Noise signal sounds best, comparison: Standard PN generator from tech kit.