Film sound codec bitrate

[Marco Giustini]

Hi all,

For educational purposes I was wondering if you could help me confirming the bitrate used by the various codecs used on 35mm film. I am aware that those differ from the consumer counterpart.

Below what I think it is correct, please do correct me if not!

DTS
Consumer (What codec? And actual 6 channels?): 1.536Mbit/s - most often half bitrate of 768Kbit/s
Cinema (APTX-100 codec - not really 6 channels but 5 channels. LFE derived from surrounds): something around 800Kbit/s
Cinema Lossless XD-10: no idea

Dolby Digital (AC3 - 6 channels)
Consumer: 640Kbit/s
Cinema: 320Kbit/s

SDDS
No idea

Thank you!

[David Ferguson]

I believe SDDS uses a version of Sony’s ATRAC codec, which they also used on their MiniDisc system.

For Dolby Digital consumer version - the bitrate depends on the settings chosen, for example it can be higher on BluRay compared to DVD.

For Dolby Digital on film, the codec is not actually AC3 - it’s an earlier variant that Dolby called EC9 and EC11 internally. It’s probably quite similar, but what exactly the differences are, I’m not sure (but I’m trying my best to find out, so if you know anything, please tell me!).

[Jim Cassedy]

On my other computer, which is currently in temporary storage, I had a really good technical document I
downloaded from somewhere which described in great detail the various codecs & bitrates between Dolby
DIgial and DTS FILM sound systems, I'll have to dig around my archive drive & see if I can find another
copy for you, since i think that's the info you're looking for. Unfortunately, if you 'Google-Search" for
that info now, 99% of the info you'll come up with online, applies to the consumer versions of Dolby &
DTS, which have different specs than the film systems.

[Marco Giustini]

David,
Thanks! I have a feeling that 640Kbit/s is Dolby Digital + and that Dolby Digital consumer is only 384Kbit/s? With DD+ used on Blu Rays.

Interesting about EC9 and EC11! And yes, Sony was ATRAC based indeed.

Thanks Jim for trying - if you manage to dig out a copy of that document, it would be great!

[Marcel Birgelen]

I remember reading somewhere that every SRD track released after a certain date and up until the present day includes the software update from EC9 to EC11, encoded into the digital optical track.

From what I've been told, EC11 and AC3 is essentially using the same audio codec, an MDCT based algorithm, like the Fraunhofer MP3 codec, only optimized for 5.1 audio. I'm not sure if EC11 refers to the digital carrier for the optical soundtrack or just the audio codec part. Maybe some of those here with some deep Dolby insighs can chime in on that one.

[David Ferguson]

The update capability of SR-D is known as the "Dynamic Loader". However I'm not sure if every print after a certain date has an update on it. I had heard that film distributors didn't like the Dynamic Loader, because it forced the processor into analog whilst the update was loaded and performed, and distributors weren't happy with this so it was only used once. It could be that I've misunderstood this, and "used once" means "one update was published, and every film now has it on it". Anyone from Dolby know?

[Pete Naples]

There hasn't been a dynamic update for probably two decades now. I don't remember it being frequent at all.

Someplace I have my scribbled notes from a SRD course at Wooton Basset.
Firmly in the last century.

I'm getting old!

[Sam Chavez]

Even older than you. Glad the car knows the way.

[Marco Giustini]

WootTon BassetT! It's even Royal now! (Not sure I ever saw that name correctly spelled! )

[Marcel Birgelen]

The update capability of SR-D is known as the "Dynamic Loader". However I'm not sure if every print after a certain date has an update on it. I had heard that film distributors didn't like the Dynamic Loader, because it forced the processor into analog whilst the update was loaded and performed, and distributors weren't happy with this so it was only used once. It could be that I've misunderstood this, and "used once" means "one update was published, and every film now has it on it". Anyone from Dolby know?

I guess the general idea was that every new movie's soundtrack contains the latest version of the firmware available upon release and that the update would only be applied if the dynamic loaded firmware had a newer version than those already on the processor. But afaik, every movie with an SRD soundtrack released after a certain date and up until today contains the "E19" update, they just never choose to update to anything newer via this route, because of the problems it caused the first time.

I think it's a clever way of updating your install base, but like every delivery method, the quality of the end-result depends on the execution. With the expansion of SRD-compatible sound processors over time, the complexity of a single-firmware distribution also increased.

[Kieran Hall]

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.

[David Ferguson]

There hasn't been a dynamic update for probably two decades now. I don't remember it being frequent at all.

Did they used to advertise when an update was being published? And what info was given out on the SRD course? I assume mainly for cinema techs on how to setup and service the equipment?

[Marco Giustini]

Thanks Kieran,
that helps.

interesting for the SDDS. DTS clearly didn’t have any error correction or backup tracks so that number should be final for the actual soundtrack.
for Dolby I’m not sure, do you think 320kb/s (assuming that number is correct) is the final actual bitrate available for the sound or including the error correction?

and yes I was surprised to see APTX alive on BT - lossless if not mistaken!

[Joe Redifer]

David,
I have a feeling that 640Kbit/s is Dolby Digital + and that Dolby Digital consumer is only 384Kbit/s? With DD+ used on Blu Rays.

Normal consumer Dolby Digital (LaserDisc, DVD, Xbox, Xbox 360, etc) can go up to 640kbps, but only if 5.1 channels are selected. Otherwise it tops out at 448kbps. It was always 48Khz. Dolby Digital Plus was introduced with Blu-ray and HD-DVD and can use higher bitrates and more channels. Dolby TrueHD on Blu-ray was lossless. 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. They also had a lossless version on Blu-ray, usually with the audio given at least a 3db boost to make it sound "better" than Dolby.

[Van Dalton]

I believe SDDS uses a version of Sony’s ATRAC codec, which they also used on their MiniDisc system.

Sony also had a bunch of CD-ROM based Walkman CD players that supported ATRAC alongside conventional MP3. It really didn't work that well and they were discontinued by the early 2010s; the whole rootkit scandal didn't help their case either since you had to use their notoriously shitty Winblows software to roll your own DRM-encumbered files. Funny thing is, the ATRAC-compatible units also didn't support the older MP2 standard, which MP3 is extended from and compatible with, so if you had discs of MP2 files (with ".MP3" filename suffix) you were screwed. Their non-ATRAC players, of course, did.

I used to use MP2/3 CD players..... a lot.

For Dolby Digital on film, the codec is not actually AC3 - it’s an earlier variant that Dolby called EC9 and EC11 internally. It’s probably quite similar, but what exactly the differences are, I’m not sure (but I’m trying my best to find out, so if you know anything, please tell me!).

From what I've been told, EC11 and AC3 is essentially using the same audio codec, an MDCT based algorithm, like the Fraunhofer MP3 codec, only optimized for 5.1 audio. I'm not sure if EC11 refers to the digital carrier for the optical soundtrack or just the audio codec part. Maybe some of those here with some deep Dolby insighs can chime in on that one.

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?

Normal consumer Dolby Digital (LaserDisc, DVD, Xbox, Xbox 360, etc) can go up to 640kbps, but only if 5.1 channels are selected. Otherwise it tops out at 448kbps. It was always 48Khz.

Now that "classic" AC3 and the MPEG1 audio layer family are all openware, I wonder how much longer it'll be before somebody writes an AC3 encoder that supports nonstandard bitrates like 640 Kb mono (if somebody hasn't by now)? For the longest time LAME would actually encode in such bizarre configurations though almost nothing was actually able to play them, at least correctly. You could encode a discrete-stereo MP3 file with LAME at 640 Kb, load it into VLC or Winamp and it'd just error out saying the file was corrupt, or just sit there and do nothing (likely scratching its head going "WTF is this?").