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Old 20th July 2007, 01:32   #1  |  Link
krassyg
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How to Record SPDIF Dolby Digital Input

What is the easiest way to record Dolby Digital SPDIF input from external source? I have the Blackmagic Intensity Card and I want to transfer the 6 Star Wars Episodes that I recorded on my SA8300HD from Cinemax. The quality of the transfer is pristine, I was really surprised. I can capture the HDMI output with no problem with a DVI stripper( DVIMAGIC ). The audio is where the problem is. The Intensity Card can capture only PCM sources, 2 ch or 5.1 ch. It cannot capture DD Bitstream at this time. What would be the easiest way to do it? My motherboard ( ABIT IP-35 PRO)has a SPDIF in and does lock onto the signal when connected to the cable box.

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Old 20th July 2007, 09:44   #2  |  Link
wonkey_monkey
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Quote:
My motherboard ( ABIT IP-35 PRO)has a SPDIF in and does lock onto the signal when connected to the cable box.
That sounds like your answer then.

I've connected a Laserdisc player (via an RF demodulator) to a USB SPDIF box and recorded the bitstream as raw audio. It needed some processing - removing the blank space between AC3 frames - and occasionally there would be skips, in which case I re-recorded.

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Old 20th July 2007, 22:45   #3  |  Link
krassyg
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Which program did you use?
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Old 21st July 2007, 16:44   #4  |  Link
krassyg
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By the way, this is what the Realtek Panel shows with PCM and AC3 signals. Notice the Data Validation difference. Could that be the problem?
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Old 25th July 2007, 15:49   #5  |  Link
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I think it was Adobe Audition, but I'm sure any regular sound recorder would have worked just as well.

No idea what that validation stuff is about. I had no such problems with my USB box, which has no idea what AC3 is

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Old 20th August 2007, 16:13   #6  |  Link
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I have a simular question.

I need to buy a card for my PC to copy the DD 5.1 AC3 stream from my HD-DVR. What pci card would you recommend to get?

I have tried on my on, but the card would only record in stereo in dolby???? a waste of money!
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Old 24th August 2007, 02:39   #7  |  Link
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AC-3 is a compressed for six channel (5.1) audio to take the space in transmitted by PCM which make it possible to use the same technology as for stereo PCM, which is can only transfer two channel within one S/PDIF cable.

What you see is that you can output AC-3 encoded or uncompressed PCM to an external decoder, but probably are limited to use stereo for digital signal (PCM).

Pulse Code Modulation is the technology where analogue signal is sampled to digital signal according to English wiki.

I did search Realteks site for ALC888 for info about input of on S/PDIF signal, but couldnt't find any clear answer to this. It could also be the driver for sound in codec that set a limit for what kind of stream that can be input.
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Old 24th August 2007, 22:02   #8  |  Link
UGC
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that is what the company said. What I bought was a turtlebeach.com DDL sound card. The way it was advertised, it looked like it would do the job I wanted. I called the company when I could not get it to record the AC3 DD 5.1, and they said the sound card would only record in stereo.

I am having a major problem finding a sound card that will record the DD5.1 toslink signal. If money was no object...what could be bought that would work? Because I am willing to spend $$ to make this happen.
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Old 25th August 2007, 00:27   #9  |  Link
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As far as the soundcard should be aware, the signal is (raw) stereo (rapidly clicking noise). Once it's recorded, it can be saved as raw audio and reformatted, removing the gaps, to create a valid AC3 file.

Your waveform should look something like |||||||||| - blocks of noise separated by slightly longer gaps.

Quote:
If money was no object...what could be bought that would work?
The simplest USB/SPDIF convertor will do (perhaps full soundcards are too clever for their own good here), but the raw recording will need processing.

David

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Old 25th August 2007, 14:27   #10  |  Link
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davidhorman>

you are correct. I did a recording, and that is what I got.

So, I am new at this.. what software do I need to convert or "process" that "raw" audio into the AC3 file? I have sony sound forge. Will that do it?

oh yeah...thanks for that info. I had no idea. I was starting to think it couldn't be done.
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Last edited by UGC; 25th August 2007 at 14:31.
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Old 25th August 2007, 23:39   #11  |  Link
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I don't know what you could use - I wrote something quick and dirty for my own use, but it's not something I'd inflict on anyone else.

David
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Old 27th August 2007, 21:43   #12  |  Link
UGC
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Thanks david for your help.

Anyone else reading this have an idea on what would process the "raw" ac3 data? What software to use? I heard a lot about besweet, would it work for this?
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Old 30th August 2007, 13:23   #13  |  Link
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Simply We all must remeber that S/PDIF work only in limited bitrates range, much more higer than limit for AC3 (which is 640kbps) so all devices which use S/PDIF as a transmission channel for AC3 must add additional data which are normally skipped by hardware decoder. So for recover raw ac3 without stuffing (stuffing men additinioal data which are added only for increase total bitrate but these data are simply discarded by decoder) special tool for removing stuffing are needed (are this can be done in some smart hex editor which can support user scripts).
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Old 30th August 2007, 17:45   #14  |  Link
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the actual plug is Toslink. But what I recorded is what is listed above.

I am about to just give up. I have searched, but with my limited knowledge about this, I haven't found an answer that I can figure out.

Nobody has recored the DD5.1 stream?
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Old 2nd September 2007, 00:14   #15  |  Link
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UGC you need a tool (or a programmer who can create such tool) for remove stuffing (padded additional bits)... I'm not a programmer but problem seems to be easy to solve by someone who is a programmer.
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Old 2nd September 2007, 04:58   #16  |  Link
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Thanks for your reply

Quote:
Originally Posted by pandy View Post
UGC you need a tool (or a programmer who can create such tool) for remove stuffing (padded additional bits)... I'm not a programmer but problem seems to be easy to solve by someone who is a programmer.
If someone has a piece of software that would do the trick, could you PM me with it.
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Old 4th September 2007, 08:25   #17  |  Link
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According to http://forum.doom9.org/showthread.php?t=56795 BeSplit is able to remove the padding.
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Old 5th September 2007, 02:28   #18  |  Link
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Thanks, I just downloaded it, and will give it a go. I will report back on how it does. lol...I have to re-install my card in my pc. I couldn't get anything to work, and the only reason I bought it was to record DD5.1, so I took it out.

*edit*
I read the thread you linked to, and also all the links in those. Looks like the card I have is not recording in a bit by bit DD stream, which means that BeSplit can not process it correctly. I tried converting some of my recordings, and I got a 0 sized ac3 file. Nothing I tried worked.
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Last edited by UGC; 5th September 2007 at 03:32. Reason: *more info*
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Old 11th March 2008, 18:45   #19  |  Link
pandy
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Quote:
Originally Posted by UGC View Post
Nothing I tried worked.
Ok, for all that need to record audio from S/PDIF.
At first you need audio card which support so called "bit matched" or "pass trough" or similar name recording mode - this mode simply record raw stream from S/PDIF input, some audio chips support them some not.
A check bit matched mode on the xfi platinum card from creative.
Bit matched mode should be supported by Emu10k2 chips - please verify this information on kx-drviers forum, dont have possibility to verify that bit matched mode is suported by other audio hardware.

For xfi we must be in so called "Audio Creation Mode", flag vor "bit matched" recording must be enabled, i use for recording part of mixer application from the creative. I simply press Record button, after few tens of second stopped. As a result i receive a file with recorded audio with .wav extension. I save them to the directory. This file have simply raw stream from S/PDIF with additional RIFF header, when we try to play them there is lot of blirps, noises etc.
For recover compressed audio we need to strip RIFF header, also we need to remove some padding bytes which are added to the stream (S/PDIF have only few, very limited bitrate speed so compressed audio bitrate - which is lower than bitrate of S/PDIF must be filled with additional data which are simply skipped or disgarded by hardware of the audio decoder).

I found two tools for making this possible:
at first: RIFFStrip v1.01 (C) 2003 By Marco Pontello
http://forum.doom9.org/showthread.php?p=842593
(Thank You Marco!)
second is:AC3Filter tools 0.1a
Copyright (c) 2007 by Alexander Vigovsky
http://ac3filter.net/releases/ac3filter_tools_0_1a
(Thank You Alexander!).

0. record raw stream by recorder (probably some kind of wav will be result of the recording)
1. remove RIFF header by RIFFStrip
2. remove padding bytes by bsconvert.exe from ac3filter tools

I think that this will be enough to solve the problems with the S/PDIF recording.

PS
sorry for my english.

PS1 I forgot to mention that AC3 and DTS are supported by bsconvert

Last edited by pandy; 11th March 2008 at 18:46. Reason: add info
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Old 11th February 2014, 23:15   #20  |  Link
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Seems that this captured DTS file makes bsconvert puzzled:

W:\>bsconvert.exe DTSDigitalSound-16bit.wav.stripped dts.dts 16le
Cannot detect file format

W:\>bsconvert.exe DTSDigitalSound-16bit.wav dts.dts 16le
Cannot detect file format

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