Dolby AC-2 codec

[Greg Miller]

I'm trying to find a way to convert (to PCM) or to play some old files which were encoded using Dolby's AC-2 codec. Supposedly these were created using a "professional" sound card that did the encoding on-board, freeing up the computer's CPU and other resources ... all ancient history.

Has anybody run into this format before? Does anybody know of a utility that would uncompress these into PCM files, or else some software that would allow direct playback?

TIA for any relevant information!

[Andrew Smith]

The first thing I do these days (and did so just recently for DIVX un-conversion) is to google for an online conversion site. There's plenty of them out there.

One that came up is https://convertio.co/aac-wav/

It might be assuming an AC3 file, but you might as well throw your AC2 file at it and see what gives.

Also, find a way to share the file with the rest of us and we might be able to assist in checking if a workflow option will succeed or not.

Andrew

[Greg Miller]

I've done a lot of googling in the past few days, with no success. AC-2 seems to be a rather obscure compression format.

I tried the file in Convertio, setting the input type to AC-3, which is the option closest to AC-2 (both are proprietary Dolby formats). The file successfully uploads to the server, but then the program throws an error message that it can't identify the file type.

[Christopher Young]

Can you upload a short AC2 file for test conversions and post a download link? It's an earlier Dolby codec that was used in radio for quite some time. Mainly hardware-based encoding and decoding from recollection. I have some ancient audio software converters here and back in the dim recesses of my hazy memory I think I had some software that could convert these files. Would just need a file to test with. When I say old software I'm talking early 2000's.

Chris Young

[Greg Miller]

Chris,

I've attached a short file for your experiments.

*NOTE* that the file extension is wrong. I had to change it because the original extension was not on the list of allowed file types.

CHANGE the extension from .WAV to .RDA before trying anything. If you use a utility to read the file header info, it will confirm that encoding is with AC-2.

Thanks for checking this out. I'll be very interested in what you find out.

Greg

[Rick Reineke]

I have never encountered a Dolby AC-2 encoded file. Have you tried an AC-3 codec. I opened the file in MedaInfo, but there are no attributes at all, MediaInfo typically states the codec, sample rate, bit rate, tracks, ect., ect., ect.

[Greg Miller]

Rick,

Thanks for your investigation. A colleague scanned the file with UNIX command "strings" which shows this at the start of the file:

FILE: 0412302S.TMP
DESCRIPTION: none
SAMPLE RATE: 32000
FILTER CUTOFF: 0
SAMPLE SIZE: 3 bits
SAMPLE FORMAT: DOLBYAC2
CHANNELS: 2
SECONDS: 59.60
SAMPLES PER BLOCK: 512
BYTES PER BLOCK: 190
EXTRA INFO: 2

I suspect there may be a lot of header info (related to the RDA container) which obscures the codec info from some utilities.

I tried two online file converters, one set as "find input type" and one manually set input to AC-3. Both of them returned errors (e.g. file type not known) when they tried to convert the file.

[Andrew Smith]

Finally, a worthy technical challenge tor those of us here on DVinfo. :-)

This is going to be good chewy fun.

Andrew

[Andrew Smith]

Just finding historical references is fun.

"Dolby AC2 is the two channel predecessor to the six channel Dolby Digital algorithm (formally Dolby AC3)
used in movie and DVD soundtracks."

http://www.audioscience.com/internet/news/pressAC2.pdf

This is at least a little more promising: https://www.computerhope.com/forum/i...topic=126787.0

Second last post to this forum page says: "I sent one of our Dolby AC2 encoded files to the sales rep at ENCO and they returned me an excellent quality PCM WAV file conversion."

So someone out there at least has the ability to convert.

Andrew

[Christopher Young]

Well, Greg!

Nothing I had would play or look at the file you uploaded.

So I thought I would talk to a couple of old mates who were in the radio business back in the '80s and they gave me some info which led to some detective work where I discovered the following information. It may be of some use to you.

Chris Young

Dolby AC-1 was the first digital coding technology introduced in 1987, A development that would later become HDTV. Later in 1989, Dolby introduced AC-2, which had better audio quality and a reduced bitrate. Finally, in 1991, Dolby introduced AC-3, which includes 5.1 channels and operates at 320 kbps.

Then in 2002 Audioscience released support on their cards for the Dolby AC-2 codec. To the best of my investigations and after talking to these fairly cluey people who were involved in the business in the late '80s early '90s I was informed that there is NO software that they were aware of that could decode AC-2 files. That the encode/decode for these files was purely embedded in DSP hardware on PCI cards. I was then pointed to the info further down.

All is not lost though. I hunted around on eBay and found the following. It's an AudioScience ASI6102 Play Only Multistream Audio Adapter MRX TSX PCI Card. US$60.00. Is it worth $60 to decode them? Your call I guess Greg. These cards have four channels of analogue audio out. See pix below. It looks like the latest drivers available for them are up to Windows 7.

Depending on the card model number, like the eBay ASI6102 PCI card I've listed below it looks like you would need driver version 4.04.14 as it is the last driver version to support the ASI60xx, ASI61xx and ASI62xx cards.

Driver downloads here:
AudioScience-Windows Drivers Old
Please note, version 4.04.14 is the last driver version to support the ASI60xx, ASI61xx and ASI62xx cards.

Driver check here:
http://audioscience.com/internet/pro...sheet_win7.pdf

FURTHER INFO:

Press Release 2002
http://www.audioscience.com/internet/news/pressAC2.pdf

FOR IMMEDIATE RELEASE

AUDIOSCIENCE SUPPORTS DOLBY AC2 PLAYBACK ON ASI6000 ADAPTERS
NEWCASTLE, DE (September-1-2002). – AudioScience Inc., a specialist in digital audio peripherals for
the broadcast and entertainment markets, has announced that it has added Dolby AC2 playback to its
ASI6000 line of audio adapters.
Dolby AC2 is the two-channel predecessor to the six-channel Dolby Digital algorithm (formally Dolby AC3)
used in movie and DVD soundtracks. Based on psychoacoustic principles, the algorithm compresses audio
by removing sounds that cannot be heard by the human ear due to phenomena of auditory masking. CD-quality audio can be maintained while using compressed bit rates of 384kbs for a stereo stream.
“The AC2 compression format was a great algorithm in its day” says Richard Gross, President of
AudioScience. “Our support of it will allow the many radio stations out there who have thousands of songs
and spots in this format, to continue using them and shows our commitment to the radio broadcast market”. Dolby AC2 support is now available for the ASI6012, ASI6122, ASI6114 and ASI6244 with driver version 2.65 on the Windows 95/98/NT/2000/XP and Linux platforms.

https://bsiusa.com/product/accessori...ience-asi5811/

AudioScience, Inc.
42C Reads Way,
Newcastle, Delaware 19720; phone +1-302-324-5333, email sales@audioscience.com. For more
information, the company’s website is at AudioScience - The Audio I/O Company


USED DEALS:

1 x AudioScience ASI6102 card eBay: US$60.00

https://www.ebay.com.au/itm/15427291...=true#viTabs_0

Or you could buy 40 of them in a bundle... only joking! :)

https://www.ebay.com.au/itm/16462093...gAAOSwPWlf8B9b

[Greg Miller]

Andrew and Chris,

Wow, thank you both for your research! Above and beyond the call of duty! You've given me answers in both directions, file conversion and file playback. Each of you unearthed info that I had not found on my own. The final decision (convert or play>re-record) will depend on the economics. Is ENCO's conversion utility free; if not, what will it cost; vs. the cost in labor to re-record and re-tag the files.

At any rate, this is good news indeed. I thank you again for your time and effort in finding this obscure information.

My best for now...
Greg

[Andrew Smith]

I expect that the WAV coming back from the Enco rep may have been to say "yes, our stuff works and your existing content is supported" and it was a hardware product back then. You'd simply have to contact Enco to find out for sure.

Please do let us know how you go.

Andrew

[Christopher Young]

Hi Greg.

I contacted ENCO and this is what I heard back from one Jeff Shelp in Support. Just waiting to hear the price as my local ENCO rep wasn't even aware the software existed.

Chris Young

------------------------------------------

"Hi Chris,

As part of our DAD automation Program, DAD can convert AC2 files to PCM16

IMAGE, see below

AudioCvt

Audio Convert is also an external program that allows the user to convert audio files and inject them into the DAD Library or convert existing Library cuts to another audio format.
Audio Convert is also an additional purchase option."

[Christopher Young]

Here is the latest! All a bit involved I'm afraid. I think I would be going down the used AudioScience ASI6102 PCI card route with Windows 7 if it's economically viable. Here is the latest info on the AC-2 conundrum.

Chris Young

----------------------------------------------------------------

"Hi Chris-

There is a little more to this process that I would like to outline since there was another similar situation here in the states where a client needed to convert these types of files recently. It is a multi-step process.

1. You need to run a program called Lib2wav.exe which is an ENCO program. This will only change the header on the file to something that AudioCVT can read. This program also only looks for .FIL files. The program is quite old and can only be run from a 32-Bit Windows XP machine and runs from a DOS command prompt.

Once the headers are changed, then AudioCVT can read these and convert them from the .FIL file to 44.1 or 48k PCM 16 WAV. Audio Convert is a keyed program from ENCO.

It may be helpful to have you send us a sample file that you are looking to convert to see if the header is even something that these legacy programs can even deal with."

[Greg Miller]

Chris,

Thanks again for all the digging you've done so far. When the ENCO rep mentioned "a similar situation here in the states" it's entirely possible that ENCO got an inquiry from the party that I'm trying to help. I think the final choice, to use ENCO or not, will depend on economics, time, and convenience.

There are some questions about the ENCO route. For one thing, the rep mentioned that Lib2wav.exe looks for the .FIL extension. But the files in question have a .RDA extension. So would Lib2wav even work on them?

The Audio Science route might be workable. Again, though, the files in question are .RDA and it's not clear whether the A.S. card will support that, or whether it needs "pure" AC2 files.

Another problem with the A.S. approach is that the files *may* contain pad data, cue in and out points, etc. Most likely those would be lost in an audio re-record solution. They would need to be manually added back (to a .BWF file). This would not be onerous with a small number of files, but I'm now told that there are a large number.

I think you've gone as far as you can go with ENCO. You seem to have gotten a fairly complete answer about the needed procedure. It might be interesting to hear the AU price of the various puzzle parts, but pricing at this end might be quite different.

I am quite tempted to buy the A.S. card and try it in an old XP machine. That would at least determine whether or not that card can handle the .RDA files. And I would be the only person on my block to have one.

I'll certainly let you know what happens at this end. And again, a big thank you for all the research done by you and others!

(BTW, if I don't come up with another question in the next week, I hope everyone here has happy holidays, and best wishes for a 2022 which had darned well be better than the last two years!.)