Cap laserdisc AC3 audio?

[KuroNeko]

How does one cap the AC3 audio off a laserdisc? Does it require a special player or will any player with optical digital out do?

TIA
Neko

[jggimi]

I found this previous thread (http://forum.doom9.org/showthread.php?s=&threadid=18230&highlight=laser+AND+ac3) using a search for "laser AND ac3".

[SeeMoreDigital]

I've captured 6Ch .ac3 audio to a 2Ch .wav audio file using my Creative SBLive sound card.

But I've not found a way of capturing an entire .ac3 stream.

If you find out how to do this please let me know!

[asifanwar]

This is how I successfully captured a 5.1 AC3 stream from my NTSC LD.

LD RF out connector -> external RF demodulator box
RF demodulator box -> CO2 converter (to convert SPDIF to optical)
CO2 converter box (as optical) -> optical IN on my sound card

Note: my Abit IS7-E mobo optical in wouldnt work, so I bought an $20 sound card with optical in that DID work. I had to select the 'reverse' option on the mixer software options, whatever the heck THAT does!
(Chaintech model AV515M, from Newegg.com of course)

I then used CoolEdit to record from the optical-in port as 'stereo 16-bit 48kHz' and it looks like white noise.

Save that as a PCM RAW file, 16-bit Motorola PCM

Rename that <file>.pcm to <file>.ac3
This will be a 'broken' AC3 file, which I then dropped onto BeSliced and told it to "Fix AC3", rendering a perfectly working 6 channel AC3 file!

You can then do with this as you please, such as split it up with BeSweet in the usual fashion etc.
I split it and then fused the various sides of the LD together into longer files, as the LD movie was split over three sides. I trimmed off the beginning and end bits of my capture too. I made a note of the EXACT timestamps I did these operations on so all six files would be altered in identical ways and they all ended up precisely the same size to 1/100th of a second. Very easy to do in CoolEdit, and I am sure in any decent audio package.

I then re-encoded the six 'mono' waves into a 5.1 384K AC3 and it sounds awesome!

Hope this helps.

AFAIK: a key point here is the RF demodulator box. I had to get one on eBay, cos they are kind of rare. There is no way around this, as the LD does NOT produce usable output in the way DVDs do.

[SeeMoreDigital]

Hi asifanwar,

This is amazing. I find it astonishing that a 2Ch CoolEdit captured file can be re-rendered by BeSliced to create a 6Ch AC3 file!

What NTSC laserdisc's did you try. Did you use a THX LD with 6Ch test audio files on them?

Another thing. Have you tried using the same proceedure with a DVD's 6Ch AC3 optical or electrical output - as a cross reference?

Now, you say the key element was purchasing the 'RF demodulator' box. I take it that this device converts an LD's electrical output to an optical output!

I only ask, as I wonder how well a sound card would work that already has an electrical input such as the Creative SBLive with Live Drive?

Really interesting stuff. Thanks!

[asifanwar]

The discs I did were a certain Trilogy...
(the Special Edition, widescreen remastered versions)

The RF demodulator takes the LD's RF output and demodulates it (duh!) into what we are used to which is SPDIF 6 channel. The same kind of thing coming out of a DVD player. I had to use the extra step of the CO2 converter as my sound card doesnt have SPDIF 'RCA-style connector' in, but only optical in.

AFAIK, there is no sound card or software that will do the job of the RF demodulator. I spent a long time reading a LOT of web pages before I embarked on this project, and they all said the same thing. If you want the AC3, you have to demodulate the signal coming out of your LD player. Some older receivers have built in demodulators, but very few modern ones do, as there is little use for RF demodulating nowadays given the DVD technology actually provides you with a usable stream already. I have not tried the method with the DVD player for several reasons:
1. it is cumbersome to take my DVD player into my bedroom
2. I wouldnt need the RF demodulator so the test wouldnt be equivalent
3. the things worked perfectly, so I am happy!
4. the damn project is finally over so I am REALLY happy! (took quite some time what with all the menu creation etc)

I am certainly no expert in this, but I really think you need one of these stupid litle RF demodulator boxes. But when it is done, the sound is really worth it! I have NEVER seen the movies like this, not even in the cinema! I dont believe there is any way around the RF demodulator to do true 6-ch AC3 (to the best of my knowledge). If someone knows different, I have never seen a method. (no flames please!)

BTW the CoolEdit file is simply a RAW data file, it is not really '2-channel' in the proper sense. After all, the 6 channels were quite happy to travel down a single wire. That's what the encoding/decoding process is all about.

[SeeMoreDigital]

Hi again asifanwar,

Do you have any info/specs you can PM me or post here regarding your RF demodulator.

I really am happy that you've licked the 6Ch LaserDisc output problem.

I've been spinning my head round this for years. Well done!

Cheers

[asifanwar]

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3028201134

This is the very item I bought on eBay, about 2 months ago. The price is about average for what these things go for, AFAIK, after having watched quite a few go by. If you do a search on eBay in the Home Electroncs section for the phrase "RF demodulator" you should find a couple. You could get it for your project and stick it back up for sale again when you are done. I decided to keep mine, as I am not sure I will find one in years to come.

OR...

You can attempt to modify your LD player yourself (yikes!)
http://www.laaudiofile.com/ac3mod.html
http://www.cybertheater.com/HW_Reviews/AC-3_Mod/ac3_mod.html
http://www.soundlabsgroup.com.au/bde/bde_ac3_kits.htm
http://www.precisionlaserdisc.com/ac3-whatisit.html

This page has a bit of technical stuff on the RF signal:
http://users.aol.com/chunter/ac-3mod.html

You may also find this interesting reading:
http://www.thadlabs.com/LD_info/ac-3_demods.txt

Please note that I am not affiliated with any of these sites,and give them in good faith for the general interest of this forum. [end of cowardly disclaimer!]

Hope this helps.

[asifanwar]

BTW, is this not in the wrong forum? Shouldnt this be in the AUDIO forum, rather than the "Capturing Video" bit?

[SeeMoreDigital]

Well you've certainly done your homework.

Being in Europe, most of us LaserDisc owners did'nt have players with AC3 output.

Also, as far as I am aware no PAL LaserDiscs were ever released with AC3 soundtracks just NTSC ones.

Ofcourse, the player situation may have changed toward the end of LaserDiscs life here in Europe. If I remember correctly a couple of manufacturers released 'combo' (LaserDisc / DVD) players which must have incorporated AC3 audio.

If so I would'nt mind getting my hands on one of these for all sorts of technical reasons!

Thanks again....

And I think you're right. This thread really should have been in the 'audio' section of the forum. As I'm sure there are many members who would find what you've done very interesting.

[jggimi]

Moved to audio forum.