Film sound codec bitrate

[Marco Giustini]

Consumer DTS (LaserDisc, DVD) used 1412 kbps (same as stereo LPCM CD audio) for 6 channels and I believe it was 48Khz unlike the cinema version

Thanks Joe
Just to point out that Consumer standard DTS is mostly used at "half bitrate" on DVDs which should be 768Kbit/s - it was a choice of whoever made the master, driven by the available space. The core DTS track from a DTS-HD version should always be the full bitrate of 1.5Mbit/s though.

[David Ferguson]

Huh. I was always under the impression that the original "film AC3" (or EC9/EC11), barring error correction and dynamic update overhead, was the same audio codec as the later consumer specification, which added many extra bitrates beyond the fixed 320Kb used in the optical version. The consumer specification being, in effect, an extension of the film version. So, in theory anyways, if you were to somehow capture the audio data stream from a print to a file and load it into e.g. Wimamp with the AC3 plugin installed, the audio would play. (I've never tried that myself for lack of equipment, and haven't heard of anybody actually doing it.) But that could also be wrong. Was that not really the case and I had misunderstood it all these years?

I wonder if they're backwards compatible if they really are that different?

I have indeed tried doing this - dumping the bytestream that goes into the Zoran "AC-3" decoder chip in the DA20, and then trying to read it on a computer, but it seems to be something unknown to any audio program! I need to take a proper look at it at some point as I'm trying to work out how the whole SR-D system works at a low level technical level.

[Van Dalton]

Interesting! Were you dumping the raw bitstream straight off the film, without extracting the audio stream from the rest? Depending what player you are using it may be that it doesn't know how to "ignore" the rest of the data in the stream and just play the audio portion. For example, the MP2 Muzak DVB audio streams on SES-3 tp 22 have an IIRC 104-byte "padding" between audio frames which Mood Media presumably use to multiplex Encompass LE control data, firmware updates and such into the stream. Most of the time I've noticed they're just null bytes (00h). The players I've used (VLC, Winamp 5.05, Kaffeine, Rockbox 3.15/IPOD 5.5 (dude so many 5s)) all seem to have trouble playing a raw Muzak MP2 CRC program stream dump as received off the satellite, either not playing at all, stuttering constantly (trying to play the inter-frame as audio), reporting wildly incorrect file lengths, etc. I usually have to demux them with PVASTRUMENTO (https://www.videohelp.com/software/PVAStrumento) on a Win32 machine to clean up the extra data and get a playable audio file. (I don't remember if PVAS will work under WINE. I think it sort of does but has issues.)

Hmmm, did you try making a copy of the Dolby stream dump file then running the copy through PVAStrumento? It might be able to produce a usable file, if ECx and AC3 are compatible. If nothing else, its status box may provide some insightful error messages. You could also try running the copy through FFMPEG with the -acodec copy parameter.

[David Ferguson]

I dumped the bytestream from a DA20 just before it enters the Zoran "AC-3" decoder chip. You're right, it likely won't have much if any padding/headers, and it'll just be the raw stream. You can download the capture if you want, as a Saleae Logic file from http://dragonsedge.hictooth.com/zora...yser.logicdata - I couldn't get any readable audio out of it, or make sense of the raw data, but I'd love you to try and let me know what you can see.

[Marcel Birgelen]

I've tried to export Channel 1 to binary, but my Logic 1.2.9 keeps on hanging. Maybe you can make a binary export of it?

It's hard to say what exactly you captured here and how it is encoded without knowing any specifics about the Zoran AC-3 decoder chip.

[Jon Dent]

Consumer DTS was 6 discreet channels, yes, and later 7 (for DTS discreet 6.1, used on the Extended LOTR DVDs and the DTS DVD of The Haunting).

It was a distinctly different system from theatrical DTS.

[Stefan Scholz]

Sony advertised SDDS has having a 2.2 Mbit/s bitrate (http://www.film-tech.com/warehouse/m...RINTMASTER.pdf), however that includes the error correction and the 'prime' tracks. I'm fairly certain that the 8 'main' channels of audio come in at 1168 kbit/s (the subwoofer track is full range; 292 kbit/s per stereo pair is the same as ATRAC on MiniDisc).

Theatrical DTS comes is 882 kbit/s (APT-x100 being exactly a 4:1 compression ratio from 44.1 kHz 16-bit LPCM). aptX (as it's now styled) lives on as a low-latency Bluetooth audio codec.

Right, as it sounds like a high bitrate on SDDS. Thinking of 10 channels (incl. overhead), LFE is a full frequency channel, and like center doubled for digital concealment mode, you get a net bit rate signigficantly higher, than AC§ Dolby. But, as Dolby uses a "bit bucketing" technology, meaning for an arthouse dialogue mono film, the full bandwith is available for the single channel, the difference is not that big, as in SDDS tracks even a 0 bit value gets the same space in the spectrum.
DTS and APT-X 100, like ATRAC 100 on SDDS are the first 1.00 release versions of the code. They are inferior to those use on consumer gear, and many MD players used 4.5 revision, that sounded audibly better. The advantage with APTXs linear prediction is a very good impulse response, just lacking precise hf resolution.

The difference between DTS, SDDS and Dolby AC 3 was audible with multi explosion blockbusters, the bit rate and model with AC3 had problems when full action was going on in all channels, and the avail bitrate lowered to around 64 k per channel. The way the LFE was handled, was pretty ingenious and space saving.
Did many patrons actually notice it? I doubt. We did the comparisons upfront theatre owner audience, and playing our Man in Black finale, just got the comments "both were loud and ugly", which relates to "the bartender, serving the beer". Not the "brewery crafting it with love". The sound systems in the rooms chosen were in general old, as 5 front channel venues were chosen, having sound systems from the 1960s magnetic no Dolby times.

[Marco Giustini]

Thanks Stefan,

Indeed it is not my intention to compare the formats and say "XYZ was better as it had higher bandwidth". It's very clear that the codec being used was pivotal in the sonic outcome.

I am just preparing a small project where I want to mention the bitrate used in the past by Cinema sound systems and compare them to what today's technology can deliver!

Can you elaborate more on how the LFE was handled in AC3? I am curious!