Help to Capture AC-3 Does anybody know how or is it a huge seceret

[beeker1959]

Help
Does anybody have any info on how to capture an AC-3 signal from a Digital Set top box into the PC either via SPDIF or Coax

[SomeJoe]

Disclaimer: I have not tested any of this. However, I did some in-depth research on this subject a few weeks back and this is what I came up with. Use this info at your own risk.

Basically, you need 2 (possible 3) things to do this:

1. If the AC3 source is from something with an RF AC3 output (like a LaserDisc player), you will need an RF demodulator to convert the RF-modulated AC3 to SPDIF coax or optical (TosLink). The least expensive one available is the Yamaha APD-1. I don't think these are made anymore, so you probably will have to get one off of e-Bay. Now, this piece is not necessary if your AC3 source is already from a box that puts out AC3 via SPDIF. Note: LaserDisc players typically also have an SPDIF coax/optical digital output, but this is NOT AC3 - it is only the digital 2-channel stereo from the LaserDisc.

A side note: SPDIF is a digital transport medium, originally defined by IEC60958. This original specification says that SPDIF is a digital PCM-only transport, capable of sending 2-channel stereo audio at 16, 20, or 24 bits, and at 32, 44.1, or 48 kHz.

Another specification was subsequently adopted, IEC61937, which says how non-PCM datastreams can be transported over SPDIF. This is how Dolby Digital (AC3) and DTS are sent via SPDIF. It is similar to a network protocol -- the 5.1 audio is compressed and stored inside DD or DTS frames. Then, these data frames are encapsulated inside the SPDIF digital headers.

2. Now, you need to capture the SPDIF stream into the computer. There are a few relatively inexpensive sound cards that can do this:

- M-Audio/Midiman Audiophile 2496
- AudioTrak Prodigy 7.1
- Several other professional-level sound cards.
- The SoundBlaster Audigy/Audigy2 will NOT work. It post-processes SPDIF input streams, resulting in non-exact captures of the digital audio. While this still works for IEC60958 SPDIF PCM audio streams, it renders IEC61937 non-PCM datastreams useless.

After you install one of these soundcards, you'll run a professional sound editor (CoolEdit Pro or Sound Forge) and set the input the the SPDIF connector on the sound card, and begin recording.

The sound editor application knows NOTHING about IEC61937 non-PCM datastreams, and will think that what you've captured is PCM audio. When you play it back, it will sound like white noise.

3. Save that white noise as a .wav file, and run BeSplit on it with a type of ddwav. BeSplit will un-encapsulate the SPDIF framing from the file and will leave you with an .ac3 file.

That will get your AC3 audio captured digitally into the computer.


Some other threads on this subject: 1, 2.

[calinb]

[QUOTE]Originally posted by SomeJoe
- The SoundBlaster Audigy/Audigy2 will NOT work. It post-processes SPDIF input streams, resulting in non-exact captures of the digital audio. While this still works for IEC60958 SPDIF PCM audio streams, it renders IEC61937 non-PCM datastreams useless.

If you nuke the Creative drivers and get the KX drivers for the Audigy2, it seems to work very well in "Direct SPDIF Record" mode:

http://kxproject.spb.ru/

[calinb]

Now that I have my Audigy2 working with the KX Drivers, how can I get BeSplit -fix functionality working as an audio codec. I'd like to perform the function real-time as I capture AC3 audio and video from my mini dish receiver.

It would be convenient not to have to demux, run the command line, <BeSplit -core( -input wave1.wav -prefix c:\ -type ddwav -fix>, and remux.

Maybe this would be a good project for me to learn to program DirectShow. (Or maybe it can be done in graphedit.)

Relevant thread:
http://forum.doom9.org/showthread.ph...ighlight=ddwav

[SomeJoe]

Originally posted by calinb
If you nuke the Creative drivers and get the KX drivers for the Audigy2, it seems to work very well in "Direct SPDIF Record" mode:

http://kxproject.spb.ru/

That's awesome. I read over those KX driver details today, and these drivers literally turn the SB Audigy into a professional level sound card. Custom routing, ASIO drivers, programmable filters, the works.

I had been holding off on buying a new sound card because some of the pro models are fairly pricey, but I might just pick up a used Audigy and give these drivers a whirl.

(A side note: The Direct SPDIF Record function is necessary for bit-accurate captures of the SPDIF datastream, but only the Emu10K-2 DSP chip is capable of the bit-accurate capture, not the Emu10K-1. Though the KX drivers support both chips, you need an Emu10K-2 chip for this function, which is available only on the Audigy and Audigy2. The older SB Live!, PCI512, and various OEM models based on the Emu10K-1 won't work.)

Even a base Audigy MP3 or Audigy Gamer can be made to work for the capture application, despite the fact that they have no SPDIF coax or Toslink input. They do have a CD Digital input on the card, which is SPDIF, but not at the coax voltages. This page has a circuit that's pretty easy and cheap to build to convert coax SPDIF to TTL-level SPDIF which can be plugged into the CD Digital input on the card. Not exactly elegant, but for less than $100, you can get AC3 capture on the computer.

[calinb]

Originally posted by SomeJoe
Even a base Audigy MP3 or Audigy Gamer can be made to work for the capture application, despite the fact that they have no SPDIF coax or Toslink input. They do have a CD Digital input on the card, which is SPDIF, but not at the coax voltages.

SomeJoe-

Good points about the Emu10K-2 vs. -1.

I have the basic Audigy2 card (no Audigy drive or EX box). I didn't even look at the logic voltage levels. The only digital input on my Audigy2 card is the CD-digital in. I have a Hoontech Digital XG card with the DB-1 bracket that has Toslink, coax, and AES/EBU I/O so I simply ran the coax out from the Hoontech to the Audigy2 Digital CD-input. It works perfectly (using digital "direct" mode in the Hoontech card, of course). If there's a logic level difference, I'm probably giving up noise margin, but it works!

Although the Hoontech driver goes bust on SCMS, it's a great digital I/O converter, especially considering the price (~$70 US). I purchased the Audigy2 specifically for the KX drivers and, given that I already had the Hoontech card, I didn't see any reason to spend the extra $100-$150 for an Audigy drive or the Platinum EX and all the extra digital I/O connections.

[e.lectronick]

[QUOTE]Originally posted by calinb

Originally posted by SomeJoe
- The SoundBlaster Audigy/Audigy2 will NOT work. It post-processes SPDIF input streams, resulting in non-exact captures of the digital audio. While this still works for IEC60958 SPDIF PCM audio streams, it renders IEC61937 non-PCM datastreams useless.

If you nuke the Creative drivers and get the KX drivers for the Audigy2, it seems to work very well in "Direct SPDIF Record" mode:

http://kxproject.spb.ru/

Hi, guys.
Just an update: while the older Audigy cards did not have a "Bit-Accurate" record mode via S/PDIF, the ZS cards do. Check this out:

http://www.soundblaster.com/products...ro/compare.asp

There's actually a tab in the control panel using Creative's native drivers that allows you to select Bit Accurate recording in software. I'm getting one!

Here's a shot of the control panel itself:

http://www.xbitlabs.com/articles/mul...igy2-zs_7.html
-Erik.

[SeeMoreDigital]

Originally posted by SomeJoe
...This page has a circuit that's pretty easy and cheap to build to convert coax SPDIF to TTL-level SPDIF which can be plugged into the CD Digital input on the card. Not exactly elegant, but for less than $100, you can get AC3 capture on the computer.

Hi SomeJoe,

Unfortunately the link you provided does not work. I would like to build one of these little devices!

This is a very useful thread. I have an Audigy card and currently use a little Creative breakout box to capture 2Ch PCM audio from optical or electrical digital sources. However, being able to capture full 6Ch audio is going to be great fun!

Cheers and thanks you guys

[SomeJoe]

Hi SeeMoreDigital,

Yes, the link I provided seems to be broken.

I found another page with a similar schematic. Try that one.


e.lectronick,

Nice to know that the new Audigy ZS cards can now capture bit-accurately. I see one of those in my future.

[rennervision]

Hello everyone. I've started looking into converting all of my laserdiscs to DVD and am curious if anyone has had any experience with this trick on a notebook PC card or an external card of some sort? I was considering the Soundblaster Audigy 2 ZS Notebook, but according to this link it does not appear it can record in bit accurate mode:

http://forums.creative.com/creativel....id=65650#M600

Furthermore, it does not look like the KX drivers currently support 24/96 with this Audigy 2 card:

http://kxproject.lugosoft.com/faq.php?language=en#Q15

So, I continued researching and came across the M-Audio Transit which
appears that it might be able to do the job:

http://www.m-audio.com/products/en_us/Transit-main.html

However, M-Audio has told me I cannot capture AC-3 with this device. To be honest, I am not so certain what to believe. Creative has e-mailed me to say none of their Soundblaster products can do this either (which I know is not true). So I suspect this could be a feature no one outside of this forum knows about! Has anyone had any experience getting the M-Audio Transit or some other external card to capture AC-3?

I appreciate anyone who can share their expertise. I readily admit I am a
complete noob to all of this, so please let me know if I should just forget about external cards altogether. If there is a possibility that going the external route will create bandwidth issues, require additional compression when using USB 1.0, result in dropped framerates or anything else, please let me know. I am planning on using a RAID 0 system on a Toshiba Qosmio G25 (XP Media Center), so I think I'll be fine, but I honestly don't know for sure.

Thanks so much!

[calinb]

Originally Posted by e.lectronick

Hi, guys.
Just an update: while the older Audigy cards did not have a "Bit-Accurate" record mode via S/PDIF,
-Erik.

Originally Posted by rennervision

I was considering the Soundblaster Audigy 2 ZS Notebook, but according to this link it does not appear it can record in bit accurate mode:

Furthermore, it does not look like the KX drivers currently support 24/96 with this Audigy 2 card:

I've captured 48/16 AC3 off spdif outputs on my DVD player and my satellite STB with a plain (no Audigy drive) Audigy2 and the KX drivers. I'm not surprised that Creative says it can't be done because they don't provide the software to do it! In most cases, you'll need drivers that ignore SCMS, like KX, and you'll need a utility to strip the null packets from the resulting file, like besplit.exe. The KX driver capture IS bit accurate. If it were resampled, you could not recover and decode the AC3. During KX beta testing of the feature, I did loopback tests with KX and diff'ed the files to prove they were identical. The capture is bit-accurate (lossless), if it's set up correctly.

96/24 support in KX is spotty and I've never tried it.

[mic]

If I remember correctly, there are a couple of threads on bit accurate recording from Lasedisc -- not sure it's possible, but again if I remember correctly.

RE: Soundblaster and bit accurate...

Best info source I've found is the driverheaven.net forums. My personal opinion is that bit-acurate spdif recording is possible on *Some* cards... This is with creative or KX drivers -- I've seen good and bad reports with both. There's usually a pretty good variety for any of their models with various OEM & value versions plus updated designs -- hopefully someone has posted yes or no for your model number (on card itself), or with notebook adapter.

As far as Audigy2 goes, simple enough to jumper connector (if it has one) to turn on extra features including controls for bit-accurate transfer to give it a shot. See the above forum for pix & details & better drivers or KX. There's also a simple control panel mod that *might* work.

An alternative if bit-accurate not possible, with the card jumpered should be able to use spdif inputs & decode ac3 with the card and record the results.

[rennervision]

Thanks, mic. I found this thread in driverheaven.net...

http://www.driverheaven.net/showthre...light=notebook

...and it pretty much confirms what I already knew that the KX drivers do not yet support the Audigy 2 ZS Notebook.

So has anyone had any luck capturing AC-3 with a USB or PC sound card for a laptop? (M-Audio's Transit was pretty much my last hope.) Or do I need to start considering internal sound cards for a desktop instead?

[bobcat56458]

I’ve just made a similar post on the “driverheaven.net > kx project audio driver support forum” in hopes of getting some answers to the below questions. I’ve resurrected this old thread because it had some useful information related to what I’m trying to achieve. I would like some information on recording the SPDIF coaxial digital audio from a Sony portable DAT tape recorder, model PCM-M1 to my Windows 98SE computer with an Audigy 1 Platinum EX soundcard, and the kx drivers version 3537. I have heard that it is possible to do bit for bit accurate transferring of the digital audio using the kX drivers. I’ve just ordered a digital I\O cable for the DAT recorder so I’ve not been able to test this feature out yet. I have some project studio DAT tapes that I would like to transfer to the computer for archiving, and editing. My questions are concerning how to best go about that process. What software will I need to record that bit for bit digital audio stream? Will it capture it as a digital stream, or as a wave file? Will it go through a digital to analogue conversion before being recorded? Will I be able to output by SPDIF the edited digital audio back to the DAT unit without an analogue to digital conversion. Any answers to these questions would be greatly appreciated. Also any tips on the kX drivers setup to accomplish this would be very helpful.

[calinb]

Originally Posted by bobcat56458

What software will I need to record that bit for bit digital audio stream?
Will it capture it as a digital stream, or as a wave file?
Will it go through a digital to analogue conversion before being recorded?
Will I be able to output by SPDIF the edited digital audio back to the DAT unit without an analogue to digital conversion.

Some time ago, I posted a few posts here and at Driverheaven on AC3 howto. Granted, they weren't too specific, but you may find them helpful. Your task will be similar, but you wish to do a full loop (return the edited file back to DAT).
I've never worked with DAT, but you should be able to do this.

I captured AC3 with KX to a wav file.

No conversion should be necessary, if setup correctly.

My tests for bit-accurate indicate you should be able to close the loop w/o losing bit-accuracy.

I created random files with a text editor, put wav headers on them (using besplit, maybe--can't recall) sent them out the Audigy2 SPDIF port and looped them back in the input SPIDIF port. When I diffed the files, after stipping the header, the code was the same. You could test files by doing a "loop and a half" and diff them. DAT >> PC (save file A) >> DAT >> PC (save file B). Then compare files A and B with a diff utility. May neeed to strip the headers and adjust offset with a hex editor first. If B contains the same data as A, you'll be set for bit-accurate conversion and editing.

My tests indicate you should be able to achieve your goals, unless the DAT deck presents problems. Sorry I don't have time to go find the details of my previous experiemtns with KX. Keep us up to date on your progress.

[bobcat56458]

Calinb: Thank you for the reply, and the information. I have not yet received the DAT coaxial digital cable, but I’ve done some tests streaming 2 channel Dolby Digital, and CD audio from a portable DVD player’s coaxial output and it worked fine. I was using the programs: Audacity, Cubase VST CE, and Wavelab lite. Has anyone been able to capture Dolby Digital 5.1 surround sound with any programs? That would be useful as a way of saving the DD5.1 surround sound from Directv Tivo programs that have it, like some HBO movies. I’m looking forward to archiving, and editing the DAT material that I have on tape, I’ll keep you posted.

[calinb]

Originally Posted by bobcat56458

I was using the programs: Audacity, Cubase VST CE, and Wavelab lite. Has anyone been able to capture Dolby Digital 5.1 surround sound with any programs? That would be useful as a way of saving the DD5.1 surround sound from Directv Tivo programs that have it, like some HBO movies.

As I recall, I captured AC3 and analog s-video from my Dish (JVC) PVR7200 using Virtualdub, Dr.DivX, and ATV2000 (http://mikecrash.wz.cz/)

They all worked fine but it's a bit of a pain 'cause you must demux the captured program, "fix" the AC3 to remove null packets with besplit, and remux with the video (with any audio skew corrections) back to a file. I always wanted to write a DSF that would do realtime AC3fixup, but never had the time. DSPguru suggested that I leverage the AC3fix project code as a start: http://dspguru.doom9.net/ac3fix.rar

Thanks for the update!

[dodone]

Does anybody know if is it possible to capture an ac3 stream trough SPDIF-in of my terratec aureon 5.1 fun?

[e.lectronick]

The one thing you need to be certain of is whether your card will perform a "Bit-accurate" capture of the ac-3 stream. In other words, will it record the stream as is, without adding any information to the signal (no extra bits or volume modifications). If it will, then you need to capture it as a 48KHz 16 bit .raw file and use BeSplit to remove the padding (null packets sent along with the stream in real time) and restore it to an .AC3 file. Refer to Rockaria's post in this thread from 15th September 2005 23:11 to see how.

-Erik
P.S. it seems that more and more sound cards these days are able to perform "bit-accurate" capture. Some are quite cheap. The M-Audio cards all do this and have terrific sounding converters to boot. I love my 2496

[dodone]

Thank you for your reply but I'm sorry I'm a kind on newbie on audio matters...
I made the capture using graphedit and i got a pcm 44khz file of an ac3 sat movie.
What should I do now? Convert the samplerate and use besplit?
If i use besplit on that file i get a 360KB ac3 file.