Film-Tech Forum ARCHIVE: DTS vs. Dolby Can you tell the difference?

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Posted by Mark Huff (Member # 480) on 05-23-2002, 02:32 AM:

My question is can the average customer tell the difference between DTS and Dolby. I am in the middle of a debate with a co-worker about the possibility of distinguishing the difference between the two.

Posted by John Wilson (Member # 269) on 05-23-2002, 06:21 AM:

Average customer? No, I don't believe so.

Personally, I can tell the difference at MY THEATRE as I know what's what, our SRD has a much more subtle feel to it and DTS is a bit harsher. Not by much, but I'm in there every day and know the system but I doubt it would be possible for me to walk into another and do the same.

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"It's not the years honey, it's the mileage". - Indiana Jones.

Posted by Chad Souder (Member # 343) on 05-23-2002, 07:40 AM:

I agree with John that DTS is a bit harsher. It seems more crisp and defined, whereas Dolby seems to have a more full, rich sound, especially in the low ranges. Perhaps a similar comparison would be a CD and a record? I have heard customers notice a difference at our theatre, but of course some of it has to do with auditorium acoustics and other factors.

Posted by Tim Turner (Member # 1109) on 05-23-2002, 09:57 AM:

Yeah Dolby has way more low range than DTS, DTS has the high range.

Posted by Evans A Criswell (Member # 381) on 05-23-2002, 10:38 AM:

I've found it very difficult to distinguish the two, since none of the auditoriums in my area have both installed. Different rooms and different sound systems have varying sound characteristics on their own. If I heard both in the same room over the same sound system, I might could learn to distinguish them over time.

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Evans A Criswell
Huntsville-Decatur Movie Theatre Information Site

Posted by Christopher Duvall (Member # 284) on 05-23-2002, 05:31 PM:

Studios and directors mix the each track differently as well. Some will pay more attention to the DTS track than the Dolby and vise-versa. I have noticed this with DVD's as well.

Posted by John Moriarty (Member # 1153) on 05-23-2002, 06:00 PM:

quote:
Studios and directors mix the each track differently as well. Some will pay more attention to the DTS track than the Dolby and vise-versa.

Why? What reason is there for not creating a single 5.1 (or 6.1) mix, and making the Dolby Digital and DTS tracks from this?

Hope this isn't a dumb question.

John

Posted by Bobby Henderson (Member # 840) on 05-23-2002, 06:00 PM:

I think some of the difference has to be in how the sound system is set up. In most theaters I've visited where DTS and Dolby Digital are both in the same rack, I usually prefer the DTS track.

I've heard Dolby Digital playback sound really good at a few theaters (the best examples I ever heard were at the deceased GCC Northpark #1 in Dallas, particularly "Crimson Tide" and "The Lion King"). However, I have to say a lot of DTS shows I saw there packed just as much oomph, if not more so. "Apollo 13" was really incredible --it felt like the rocket was taking off in the theater. Really cool.

I've also heard Dolby Digital playback that was absolutely horrible. I watched "Kiss the Girls" in a then-brand new THX theater in Wichita Falls, TX run by Carmike. The screen was newly tuned, had a new Dolby CP-500 processor, QSC amps, everything top notch. The sound quality still sucked. I come back up to Lawton, watch the same film again in a different THX auditorium using a Dolby CP-65, DTS-6 and QSC amps --noticeably better quality. Years later, I revisit the film on DVD and listen to it with a higher bitrate (448kb/s) Dolby Digital track and the film sounded good.

Some of the differences, I'm sure, have to do with different audio masters being used for the encoding process. I've been less than impressed with some DTS shows; whereas others just simply walloped with really great quality audio. "Casper" of all films goes down as having one of the most walloping balls-to-the-wall DTS mixes I have ever heard. The bass on that one was just incredible.

Of the previous posts, I'm pretty surprised at the "DTS is harsher" comments. I usually find the reverse to be true.

Posted by David Baum (Member # 568) on 05-23-2002, 06:03 PM:

well, surprised to see the comments here.
first, let's not forget that the LFE channel of DTS is in the surrounds (Cinema DTS) and often "less" pushed up as the LFE in Dolby digital mixes. On the otherhand, DTS mixes often have more bass in the front channels...
Also, Dolby combines channels as certain frequencies... DTS remain constantly discrete, full range, on all channels.
This can also be heard on dvds, where the DTS track seems often more violent, "more free" and more "demanding" on the system you use, while the dolby tracks often has that same "pumped up" LFE channel... Another reason why it's better at home to listen in the SMALL mode and leave the subwoofers do the job, unless you have VERY LARGE and VERY RARE ( if not very expensive ) speakers...

A good rule of thinking is this imho: first, the mix itself. then the codec. a bad mix won't transform itself into a superb mix just because dts or sdds is used. but a good mix will sound better when switching from dolby to dts...

Posted by David Stambaugh (Member # 1102) on 05-23-2002, 07:22 PM:

Someone would have to calibrate each system very carefully to do a valid A-B listening test. Even just a slight difference in levels or EQ, or a cinema processor with a little "noise" in the signal path or something, would possibly be enough to skew the results. And you would want to be able to switch format on the fly.

So having said all that, I really can't notice any difference. Sometimes if I don't know what the format is, I'll try to guess, then ask them later, and I often turn out to be wrong. In the early days of digital sound it seemed like dropouts were the best clue. DTS almost never had dropouts, even from the beginning. SR-D seems to have gotten a LOT better in that department since it first came out (why did SR-D almost always have dropouts at reel change splices in the early days? Has improved software helped mask dropouts?).

I remember the first time I found out I had just sat through a movie in SDDS (which I thought sounded excellent), but I was sure it had to be DTS or SR-D because of the SDDS harshness issue others have commented on (which turns out to be more of an EQ problem than something inherently wrong with SDDS).

In a blind A-B comparison with "normal" film sound and properly-calibrated hardware, I bet very few people could tell any difference.

Posted by Brad Miller (Member # 2) on 05-23-2002, 08:08 PM:

The only FAIR way to do it is to have all 3 formats in one sound system, and to bypass all of the SDDS internal EQing and route it "flat" into the analog processor so that all 3 formats share the exact same EQ settings and of course all formats must be exactly level matched as well. That being said, I don't think any typical customer would ever be able to tell the difference between the formats. I've done many an A/B comparison in more than one auditorium and indeed they are VERY close. Funny as it may sound, some movies on the A/B (or A/B/C) tests just sound better in one format as opposed to another. Generally I've found SDDS to be the winner, but of course NEVER when the internal EQing was used.

Regarding the masters, I've always understood that there was one master mix that was sent to all 3 companies for encoding into their respective formats (special 8 channel SDDS mixes are the exception, of course). Perhaps someone from Dolby, dts or sdds can comment.

Posted by Phil Hill (Member # 371) on 05-23-2002, 08:40 PM:

While it is true that the only fair evaluation is to use the same sound system amplifiers, EQ's, speakers, and auditorium...it is not true to use the same EQ settings. Each format should be referenced and EQ'd to the ISO standard.

I doubt if anyone could tell the difference. In fact, I think most, if not all, patrons could tell the difference between analog multi-channel and any digital format in a properly set-up theater.

Also, I fail to see what the recording of the DTS LFE in the surrounds has to do with anything since the surround speakers only reproduce frequencies far above that range. Excepting of course Special Venue point-source rear/surround speakers.

>>> Phil

Posted by Brad Miller (Member # 2) on 05-23-2002, 10:08 PM:

Ummm, Phil, care to clarify? Example sound system:

CP200
SDDS DFP-2500
DTS 6-D
DA20

And how are you suggesting the calibration should differ?

Posted by Jonathan M. Crist (Member # 413) on 05-24-2002, 12:24 PM:

I recall about three years ago (just before the first "Mummy' came out) that there were notices placed in the print cans that the subwoffer channel of the DTS mix was going to be 'downsized' and from that point on it would be necessary to increase the amp output on the subwooffer channel for DTS playback to compensate for this mix.

Posted by Phil Hill (Member # 371) on 05-24-2002, 04:27 PM:

I'm not suggesting that the calibration should be different....I am saying it should be the same. With a single EQ setting, typically in the "B" chain, one has to ensure that all "A" chain film format sources are tweaked flat and set to the proper playback reference levels for that format. The audio system should be set up so the auditorium has the same electro-acoustical response no matter which film sound format is playing.

>>> Phil

Posted by Bobby Henderson (Member # 840) on 05-25-2002, 02:26 PM:

It is kind of interesting just how different the DTS and Dolby Digital formats are between their professional cinema versions and home theater versions.

Dolby Digital uses the same AC-3 compression system on both cinema and home formats, but the home formats typically run at higher data rates (320kb/s for cinema, 384kb/s and 448kb/s for DVD). Dolby Digital uses a copy protection system which prevents home Dolby Digital decoders from playing the DD bitstream off a 35mm print.

While DTS theatrical is actually a 5.0 format with the LFE in the surround channels (the advantage is even milder data compression levels on the 820 kilobit per second track), the home theater version uses a totally different compression format, a wider range of data rates, full range surrounds, separate subwoofer channel and the added option of DTS-ES Discrete 6.1.

The point with all this is that many DVDs don't sound very much like their theatrical counterparts. On action films the bass and surrounds usually seem more pumped up. But on some dramas and comedies the audio track may be more conservative than the previous theatrical release.

I think DTS has more of an advantage against Dolby Digital on DVD than it does in the commercial cinemas. One of the biggest advantages is that a DTS 5.1 or 6.1 mix on DVD is never compromised with a downmixing scheme that hamstrings so many DD 5.1 tracks. Then you have the true Discrete 6.1 thing Dolby Digital is unable to do. I also believe the higher bitrates and lower compression levels give DTS an additional advantage. That, and the reliability of the dual system approach, is also why DTS is my favorite of the theatrical systems.

Posted by David Baum (Member # 568) on 05-25-2002, 06:59 PM:

Bobby

you're absolutely right! one of the big no no with Dolby digital in home version on dvd is the downmixing preparation that affects the dynamics of the sound. Most studios cook down the mix when encoded in Dolby digital to allow the majority of dvd consumers to play the track in stereo or dolby surround on their tvs or "cheap" or old A/V systems. At least a DTS track can't be affected this way: it can only be played in... DTS . A "free" DTS track is more demanding on the audio chain (amps, speakers, room accoustics etc).
A 448 Dolby loses 92% of the original PCM master information (compression ratio of 15:1)
A 754 DTS loses 83% (compression ratio of 6:1)
A 1509 DTS loses 67% ( compression ratio of 3:1)
The argument of many is that, anyway, the ears can perceive those 92% lost....since most of these sounds are either beyond the treshold of audibility or covered by louder sounds in the mix. yeah yeah
There's also the dialnorm issue which is not used in theaters of course. Though its use on dvds "can" be accepted , it's improper use is something unacceptable. Sometimes the improper dialnorm level creates an offset on the processor by as much 12db sometimes! (lower!). Dialnorm affects the efficiency of the N/A converters says DTS.

Posted by Lyle Romer (Member # 1266) on 05-27-2002, 10:43 AM:

David,

Audio data reduction is not that simple. Just because you are missing x% of the bits does not mean you are missing x% of the audio signal. For instance, Delta PCM is a completely lossless coding scheme that has only 1/2 the number of bits recorded. It works by coding the difference between the current sample and the next sample. Upon decoding, 100% of the original information is there.

Dolby's AC-3 codec (and I believe DTS' Coherent Acoustics codec also) is a transform codec. The time domain PCM information is recorded as a set of frequency domain fourier transforms. This step alone gives a large amount of compression. For the most part with AC-3 data is not just thrown away. The number of bits used to code a forier coefficient is varied based on psychoacoustic masking techniques, ie. a loud 1 khz sound on the center channel will mask a soft 1 khz sound on the right channel so the right channel sound is given less bits (more noise) when it's coded. After this bit sharing is complete, some other techniques are used to get further reduction when needed and as a last resort some info is thrown away completely.

As to the original question, theatrical DTS and DD probably sound a little different. As to which sounds better, that's a tough one. Maybe somebody could design a blind test setup and invite some people to rate the two systems in the same theatre. I believe that Dolby did this once with an audience and the results came out with most people prefering the sound of Dolby Digital. Just the fact that there is a debate (when theatrical DTS is lossless compression) proves that 320 kbps AC-3 is not missing >90% of the PCM information when decoded.

I do tend to prefer DTS on DVD only because it does not get altered at all by the processor but the difference would not get me to spend extra money on a DTS DVD vs a DD one.

Posted by David Stambaugh (Member # 1102) on 05-27-2002, 11:23 AM:

Lyle, thanks for straightening this thread out on the issue of lossy vs. lossless compression.

"Compressed" does not necessarily mean that any of the original data has been lost. Think of file compression utilities like WinZip: It can compress files by a factor of 90% or more, but no data is lost.

Posted by Bobby Henderson (Member # 840) on 05-27-2002, 01:11 PM:

The APT-X100 codec used by DTS Theatrial is not a data lossless encoder. It is a simple waveform based codec running at a 4:1 compression ratio (16-bits, 44.1kHz, 5.0 channels at 820kb/s).

Dolby Digital uses a Cosine Transform encoder and SDDS uses what they call as Adaptive Transform encoder. Increased levels of compression are gained when you take an audio sample and turn it 90 degrees out of phase. Unfortunately, you also gain abberations in the audio and permanently lose even more of the original audio detail. Psychoacoustical masking has to be used to devote more bits and volume intensity levels to particular channels to mask out others in the background that listeners may not be able to hear anyway. Generally, the process works pretty well, but at low bitrate levels certain kinds of audio (music in particular) really fall apart.

Sony's MiniDisc format uses Consumer ATRAC encoding, which is similar to the Professional ATRAC encoding used in SDDS. MiniDisc recordings often sound pretty thin and trebly compared to their PCM Music CD counterparts.

Home DTS uses transform encoding, bitpooling and other "more advanced" techniques than its theatrical waveform counterpart. However, DTS operates at high enough bit rates that items like music material often sound better than a DD 5.1 counterpart. The best DTS material on DVD is usually encoded at the 1509kb/s bitrate instead of the lower 754kb/s data rate. Unfortunately, many DVD content creators think 754kb/s is good enough. On some movies yes, but for music oriented stuff I say you have to go with 1509kb/s. DTS music CDs use a 1234.8kb/s data rate. DTS Theatrical operates at only one fixed data rate, 820kb/s.

Digital Cinema often features uncompressed 20-bit Linear PCM 5.1 audio, and I think that is one of the only really good things about such setups at this point. The sound format is a no-compromise solution. It is just too bad the same cannot be said for the picture.

Using DVD-ROM discs, uncompressed LPCM 5.1 could be delivered for film prints via things such as a new generation of DTS machines. Even 10.2 Surround would be a good possibility. 70mm 10.2 Surround is the real brass ring of high quality film production and presentation should hit.

Posted by David Stambaugh (Member # 1102) on 05-27-2002, 02:31 PM:

I didn't mean to imply that DTS or AC-3 are lossless. I was pointing out as Lyle said that x% compression can be achieved with much less than x% loss of the original data (or possibly no loss at all, depending on the scheme).

Posted by Gordon McLeod (Member # 33) on 05-27-2002, 06:51 PM:

I think the points made by Lyle are drifting of the point of film technolgy as was the comment on winzip they are not what is being delt with (in this forum film handlers)
DTS typically has less losses of raw data and is on playback almost imprecivable from the original master the other systems relie on masking which is not an accurate reproduction of the original
Also in the UK there were blind test performed and were reported in a BKSTS journal

Posted by David Stambaugh (Member # 1102) on 05-27-2002, 07:02 PM:

Winzip was mentioned because it's an example of lossless compression of digital data that everyone can relate to (how many film-techers have a deep understanding of film sound compression schemes? Probably not many). The thread had already drifted into a discussion of film sound compression technology and Lyle corrected some earlier statements that were seriously in error.

Posted by Bobby Henderson (Member # 840) on 05-27-2002, 11:16 PM:

Actually, I brought up DTS' APT X-100 encoder being data lossy and not lossless over something Lyle said --aside from the other corrections he made.

What DTS theatrical does is really kind of at the limits for how 16-bit 44.1kHz audio can be compressed. A great many radio stations use audio servers for music playback and much of their material is data compressed in a very similar manner and identical 4:1 data compression ratio. DTS just kind of hit the "sweet spot" on an acceptable level of audio quality while being able to fit 100 minutes of 5.0 audio onto a CD-ROM disc.