Capturing digital audio from Laserdisk

[egrimisu]

Hi,
i'm not sure this is the right thread but i haven't found any audio thread :)
my question i that is possible to rip digital audio from LD to pc via digital spdif port. the audio port in the pc is a spdif optical port and the same is on the ld player.

ld player back : http://img28.imageshack.us/img28/4808/dvlt0390909.jpg

And waht app do i need to achieve this if possible. Thanks

[Ghitulescu]

I think even Recorder (standard windows distribution) can do this, but any other audio should be capable of capturing the S/P-DIF signal. The signal may be flagged as "Copy prohibit" but this generally doesn't pose any problems to PC. Be aware that, according to the output and the disk, AC-3 signals may be transferred.

[ChiDragon]

Pray that your audio path is capable of bit-perfect recording and use this. :o

http://www.avsforum.com/avs-vb/showthread.php?p=19329763#post19329763

EDIT: Thought you were doing AC3 recording. You can just use any sound recorder for PCM, but testing AC3 is useful if you care whether your card is doing resampling.

[egrimisu]

thanks guys for the quick reply,
unfortunetly i just found out that my onboard audio card has only spdif optical and rca OUT , no IN :( . My goal is to record the ac3 track that is avaialbe on the laserdisc, lossless if possible or at good audio quality with no noise, i read the upper thread and found out that i need a good audio card that support bitperfect recording. I would buy a card like that, do you know any?

[Lyle_JP]

thanks guys for the quick reply,
unfortunetly i just found out that my onboard audio card has only spdif optical and rca OUT , no IN :( . My goal is to record the ac3 track that is avaialbe on the laserdisc, lossless if possible or at good audio quality with no noise, i read the upper thread and found out that i need a good audio card that support bitperfect recording. I would buy a card like that, do you know any?

You'll also need an RF demodulator to extract the AC-3 signal from the analog channel in which it is recorded. You can't use the laserdisc player's PCM out for anything but PCM stereo or DTS, and the AC-3 RF-out is gibberish without the demodulator. Lossless is not possible, since all AC-3 sound on laserdisc is encoded at 384 kbps, well below transparent, much less lossless.

[Ghitulescu]

Ignore the message above, the output is clearly indicated as PCM/DD, so it would output dolby digital, this way the LD player can be connected to any AVR that has coax/toslink in and understand PCM and DD.

So go in a music shop, not in computer one, and ask for the cheapest M-audio card (~100€) with digital in. All cards with digital in should not interpret the signal (unless they are specially designed to do so, as this adds heavy licencing costs for things nobody needs in the music industry), however the kmixer module of windows would resample the signal, unless replaced with ASIO. Don't go for creative, don't go for other super PC card, they won't be useful for dolby digital and the PCM won't be lossless.

[Lyle_JP]

Ignore the message above, the output is clearly indicated as PCM/DD, so it would output dolby digital, this way the LD player can be connected to any AVR that has coax/toslink in and understand PCM and DD.

Ignore my message at your own peril. Or just read this. (http://en.wikipedia.org/wiki/Laserdisc#Audio) Or this. (http://forum.doom9.org/showthread.php?p=100635#post100635) Or this. (http://forum.videohelp.com/threads/136335-How-to-capture-AC3-from-Laserdisc-on-your-PC?p=635663&viewfull=1#post635663) Or this.
(http://www.precisionlaserdisc.com/newfaq.html)

[Ghitulescu]

While it depends on the player whether it decodes or not the AC-3 signal or the PCM or whatever digital audio may be there, if digital outputs are marked with DD then they should output DD. I'm not familiar with this model, but the output you mention, DD-RF output, seems to me to be another alternative to output the sound, a sort of Source Direct many players have. AFAIK there's no standard of sending DD-RF through the optical fibre.
The best information should be as always the manual.

[Lyle_JP]

While it depends on the player whether it decodes or not the AC-3 signal or the PCM or whatever digital audio may be there, if digital outputs are marked with DD then they should output DD. I'm not familiar with this model, but the output you mention, DD-RF output, seems to me to be another alternative to output the sound, a sort of Source Direct many players have. AFAIK there's no standard of sending DD-RF through the optical fibre.
The best information should be as always the manual.

Your confusion comes from the fact that the photograph is most likely from a DVD/LD combo player (other than the champagne color of the side and top cover, this looks exactly like the back of a DVL-909). The PCM/DD outputs only work with DVD playback. AC-3 sound from laserdiscs will only be output through the connector marked RF OUT(AC-3)(LD). No LD player manufactured that I'm familiar with had a built-in demodulator.

EDIT: After further research, I see that there was one. It was a boutique player by MSB called the MSB Silver (which was actually a modded Panasonic LX900). But not all MSB Silvers even had the built-in demodulator; it was a $600 additional feature. I've never seen one of these players in the wild.

[Ghitulescu]

Yes, DVL-909 does not have a demodulator. You must be right.
The OP should have mentioned his model.

EDIT: how to capture AC-3 using S/P-DIF -> http://forum.doom9.org/showthread.php?t=128135

[laserfan]

ld player back : http://img28.imageshack.us/img28/4808/dvlt0390909.jpg
Please advise your player model. I was puzzled too about DD vs. AC3 RF until Lyle_JP's excellent posts about it.

I very vaguely recall that there is some magic associated even with the output of an AC3 RF Decoder that needs to be dealt with before the soundtrack can be used--possibly a sampling conversion or something.

I had saved some old URLs on the subject, but they are all broken/abandoned now. :(

[Lyle_JP]

I very vaguely recall that there is some magic associated even with the output of an AC3 RF Decoder that needs to be dealt with before the soundtrack can be used--possibly a sampling conversion or something.

Laserdisc AC-3 had a sampling rate of 44.1 khz, rather than the DVD standard of 48 khz. Is this what you mean?

[laserfan]

Laserdisc AC-3 had a sampling rate of 44.1 khz, rather than the DVD standard of 48 khz. Is this what you mean?I'm not certain what I mean! ;)

Here is a post lifted from this web page (http://www.macintouch.com/audioconvert02.html) which discusses some of the issues, and contradicts your 44.1 assertion:

Toren Kelly Smith
In response to Will Collier's mail about capturing Dolby Digital streams from LaserDiscs: I've done this, albeit on a PC -- unfortunately I've never had the opportunity to try it on a G5. To do this you need the following:

* If your LD player's AC3 output (AC3 = Dolby Digital) is AC3-RF, then you either need a separate AC3 demodulator, or a receiver that has an AC3-RF input and a digital output. LaserDiscs store Dolby Digital streams as an RF-modulated signal, which must be demodulated before it can be fed to a normal digital input.
* You need an audio capture device with a digital input that will not alter the digital signal being captured; many PC sound cards will resample incoming digital audio to their own clock signal, which destroys the AC3 signal. I found that sound cards based on the C-Media 8738 chip will capture the exact bits being sent, and worked perfectly. I don't know whether the G5's Toslink input resamples the inputs or not -- given its pro-audio appeal, I would sure hope not.
* Your sound card will need to be able to capture a non-PCM stream as if it were PCM. (PCM = uncompressed audio) Digital audio streams containing an AC3 signal have the "private data" bit set, which should tell devices that they should not interpret the information as uncompressed audio. My sound card's driver has an option to ignore this bit, so it can capture the signal regardless. Some other sound cards are too dumb to notice the bit either way. I'm not sure how the G5 handles this.
* Once those are satisfied, you'll be able to capture the AC3 signal in its transport format, which embeds the compressed AC3 information inside a 48KHz PCM uncompressed audio stream. Since the S/PDIF (and Toslink, its optical format) standard is designed to transmit PCM audio data, AC3 signals are padded out to this larger size. The resulting file will sound like buzzing garbage as a PCM AIFF file, and isn't a valid AC3 file. For that you'll need a program which can strip out the padding of the file and write out the smaller AC3 file. I wrote a quick & dirty program for this on Windows for my purposes, but there may be such a thing for MacOS or UNIX -- I'm not sure.

After all that, you'll end up with a valid AC3 file that should be able to be imported into DVDSP or another DVD authoring program. It is definitely the case that the AC3 signal stored on LaserDiscs matches that of DVDs: it's a 48KHz Dolby Digital stream, just RF-modulated for storage.

[Lyle_JP]

I'm not certain what I mean! ;)

Here is a post lifted from this web page (http://www.macintouch.com/audioconvert02.html) which discusses some of the issues, and contradicts your 44.1 assertion:

I could be confusing AC-3 on laserdisc with DTS on laserdisc, which was definitely at the 44.1 khz sampling rate (same specs as DTS-CD) wrapped in a PCM stream. I didn't know about AC-3 being padded to PCM size, but I guess it must be part of the DD spec since every DD receiver made can decode an AC-3 signal from laserdisc once it has been demodulated.