capturing laserdisc ac-3 5.1 channels simultaneously?

[clashradio]

Just curious if it's possible to capture the 5.1 ac-3 channels from a laserdisc simultaneously as one track, with all channels in sync sort-of like a multi-track recording?

I'm newbie to the ac-3 RF track on LD's; was only concerned about the 2-channel pcm track for years but now I want to include the 5.1 track when I do my LD captures to BD.

I know I need to demodulate the RF signal from the disc and in doing research I ran into two different types of devices for this; a processor and a demodulator.

Seems a processor has rca coax RF input, then all the channels are analog rca-outs. And a demodulator has rca coax RF input, with either a single rca coax-out or toslink-out for Dolby Digital.

Do I capture each channel separately with a processor and sync them up the best I can in my NLE, or does using a demodulator make it possible to capture all channels simultaneously with the proper soundcard that can record multi-track?

I am using a Fosucrite Scarlett 18i6 soundcard which I believe is capable of multi-track recording from either coax or toslink. Just not sure if it will recognize the demodulated signal as a multi-track.

Ideally I'd like to capture simultaneously as then I'd know the channels would be in sync. Plus I wouldn't have the play the movie 3 times to capture the LR/RF/Center/RL/RR/sub

[usually_quiet]

I doubt that the Focusrite 18i6 can capture 5.1 ac-3 out from the ac-3 RF demodulator. The Focusrite 18i6 is an audio interface used for mixing input from various audio sources. The documentation I found indicates that the Focusrite 18i6's optical audio port is an ADAT port, not an S/PDIF port. The Focusrite 18i6 has an RCA S/PDIF port, which is only for stereo audio input, and almost certainly PCM, not Dolby Digital.

Don't buy any more expensive gear to use for this project if you don't understand how you will use it. If someone else is recommending this stuff to you, stop listening to him/her unless he/she can personally demonstrate how to use it for capturing the output of a LD player.

[clashradio]

First off [usually quiet] I want to thank you for all of your help on my laserdisc-to-BD post, & apologize for not totally understanding all of your information. You took your time to try to help and I just wasn't grasping, and I'm sorry.

My buddy who recommend the 18i6 mainly deals with recording musicians and multi-tracking etc. I have a standard consumer mini-disc player (that has optical in/out) & I wanted to transfer those discs to my PC via the 18i6 using the optical toslink. The 18i6 wouldn't recognize the signal. But we inputed a multi-track recording from his mixer and walla...signal/sound. We didn't take the time to see if I could record each channel. But since I got a signal I figured it was something to do with multi-tracking. Same went for a non-encrypted dvd; When I tried to capture the audio from a dvd player via toslink into the mini-disc deck...no signal. The mini-disc deck will record analog all day however.

So like you said, before I buy an expensive demodulator, I'd like to know if the 18i6 would treat the signal coming from the demolulator as a multi-track signal? or do I play it safe and buy a processor instead? With the processor you get the separate rca-output channels which I can then record separately and then import the four tracks (left front/right front, center, right rear/left rear, sub) into my NLE which supports multi-track audio.

Do you know why an audio processor cost significantly less than a demodulator?

What quantization would you recommend capturing the ac-3 audio at? Wouldn't make since capturing WAVE 16b/44k right? (I know that's what the pcm track is). Would 384kbps mp3 be a closer match?

oh, I wanted to add; I think one reason the 18i6 won't capture 2-track stereo has something to do with Low Latency?

[usually_quiet]

I have a standard consumer mini-disc player (that has optical in/out) & I wanted to transfer those discs to my PC via the 18i6 using the optical toslink. The 18i6 wouldn't recognize the signal. But we inputed a multi-track recording from his mixer and walla...signal/sound. We didn't take the time to see if I could record each channel. But since I got a signal I figured it was something to do with multi-tracking. Same went for a non-encrypted dvd; When I tried to capture the audio from a dvd player via toslink into the mini-disc deck...no signal.

You are trying to record digital signals that don't match the type of signal the recording device can accept through the connection that you are using.

If you see a Toslink port on a consumer electronic device, it is for optical S/PDIF. If you see a Toslink port on pro sound equipment, there is a very good chance that it is for ADAT. ADAT ports only accept ADAT signals and optical S/PDIF ports only accept S/PDIF signals, even if they look the same and take a Toslink cable. This means the signal from an optical S/PDIF output on a consumer electronic device like an AC3 RF demodulator or a Minidisc player won't be recognized if you connect them to an ADAT port like the one on the Focusrite 18i6.

The Minidisc player probably only accepts digital audio if it is unprotected 2-channel LPCM audio. The audio signal carried by Toslink out from a DVD player may be copy protected, especially coming from a commercially produced disc. ...or the audio may be a 5.1 channel AC3 stream if it is from a DVD.

So like you said, before I buy an expensive demodulator, I'd like to know if the 18i6 would treat the signal coming from the demolulator as a multi-track signal? or do I play it safe and buy a processor instead? With the processor you get the separate rca-output channels which I can then record separately and then import the four tracks (left front/right front, center, right rear/left rear, sub) into my NLE which supports multi-track audio.

I think I just answered that. If you have to use the Focusrite then you need the processor. I hope your buddy can help you with this. I know nothing about using a mixer.

Do you know why an audio processor cost significantly less than a demodulator?

I don't know but my guess is that audio processors are either more common or less sought after.

What quantization would you recommend capturing the ac-3 audio at? Wouldn't make since capturing WAVE 16b/44k right? (I know that's what the pcm track is). Would 384kbps mp3 be a closer match?

These questions make no sense to me.

FWIW, I would be trying to capture the 5.1 channel AC3 audio with one of the Hauppauge video capture devices able to record the identical 5.1 channel AC3 stream received as input.

[clashradio]

[QUOTE= This means the signal from an optical S/PDIF output on a consumer electronic device like an AC3 RF demodulator or a Minidisc player won't be recognized if you connect them to an ADAT port like the one on the Focusrite 18i6. [/QUOTE]

I'm sure that's it. That has to be why the 18i6 doesn't recognize the mini-disc player.

[QUOTE= The Minidisc player probably only accepts digital audio if it is unprotected 2-channel LPCM audio. The audio signal carried by Toslink out from a DVD player may be copy protected, especially coming from a commercially produced disc. ...or the audio may be a 5.1 channel AC3 stream if it is from a DVD. [/QUOTE]

I'll have to experiment with an unencrypted 2-channel mix dvd

What quantization would you recommend capturing the ac-3 audio at? Wouldn't make since capturing WAVE 16b/44k right? (I know that's what the pcm track is). Would 384kbps mp3 be a closer match?

These questions make no sense to me.

I guess what I was asking, albeit not very clearly was since Video audio contains Lpcm and ac-3 (and also DTS), and Redbook audio is Wav and mp3 (I know there are a million other compressed files besides mp3) I think of pcm as wav and ac-3 as mp3. I was wondering if capturing mp3 as a wav file would have any benefits. Sort-of like how BD's contain dts-ma audio, if capturing the ac-3 at 16/44 or 16/48 wav would be the same as if the 5.1 track is now dts quality.

[usually_quiet]

I guess what I was asking, albeit not very clearly was since Video audio contains Lpcm and ac-3 (and also DTS), and Redbook audio is Wav and mp3 (I know there are a million other compressed files besides mp3) I think of pcm as wav and ac-3 as mp3. I was wondering if capturing mp3 as a wav file would have any benefits. Sort-of like how BD's contain dts-ma audio, if capturing the ac-3 at 16/44 or 16/48 wav would be the same as if the 5.1 track is now dts quality.

No. An MP3 file or AC3 file that has been decoded to LPCM, sampled at 16/44 or 16/48, then stored a WAV file doesn't provide better quality than the original MP3 file or AC3 file. The only advantage is it can now be used with something that accepts WAV files, but not AC3 or MP3 files.

Dolby/AC3, DTS, and MP3/MPEG-1 Audio Layer III are all lossy types of compression. "Lossy" means that some of the audio information contained in the original uncompressed digital audio is discarded when it is encoded to these formats. The discarded information is not restored when AC3, DTS or MP3 files are decoded to an uncompressed format. It is gone forever.

DTS-HD Master Audio and Dolby TrueHD are lossless compressed formats. No audio information is discarded when the original uncompressed audio is encoded, so the original uncompressed audio is fully restored when they are decoded.

[clashradio]

[QUOTE=usually_quiet;2504878]

Dolby/AC3, DTS, and MP3/MPEG-1 Audio Layer III are all lossy types of compression. "Lossy" means that some of the audio information contained in the original uncompressed digital audio is discarded when it is encoded to these formats. The discarded information is not restored when AC3, DTS or MP3 files are decoded to an uncompressed format. It is gone forever.

Ok, I was thinking once it's compressed it's gone forever.

What I was trying to ask in my first post was; since ac-3 is compressed, and since my 18i6 is capable of multi-track recording (from the eight 1/8" analog jacks) what bit rate and frequency should I record at as an mp3? It's a waste of space recording at WAV 16/44. Do you know the equivalent ac-3 audio (for LD). I know dvd ac-3 is a little bit higher than 384mbps.

From what I understand, if you extract a Lpcm track from a LD to say a cd recorder, the quantization would be WAV 16/44 for LD, 16/48 for dvd.

[usually_quiet]

Ok, I was thinking once it's compressed it's gone forever.

What I was trying to ask in my first post was; since ac-3 is compressed, and since my 18i6 is capable of multi-track recording (from the eight 1/8" analog jacks) what bit rate and frequency should I record at as an mp3? It's a waste of space recording at WAV 16/44. Do you know the equivalent ac-3 audio (for LD). I know dvd ac-3 is a little bit higher than 384mbps.

From what I understand, if you extract a Lpcm track from a LD to say a cd recorder, the quantization would be WAV 16/44 for LD, 16/48 for dvd.

I know nothing about encoding MP3 audio or mixing. Why do you think you should use MP3 for audio? AC3 has wider support than MP3 when combined with video in a media file.

LD AC3 characteristics obtained from: http://originaltrilogy.com/topic/Why-laserdisc-soundtracks-are-better/id/15519:

The AC3 soundtrack has always the 384kbps bitrate at 48KHz, almost always 20bit 5.1 channels

I don't think I can help you any further. I don't have the knowledge you need.

[clashradio]

I didn't know I could capture as an ac-3 file? I've never been interested in ac-3 for the longest time, or 5.1 audio for that matter. But I think it would be neat to have a BD with 5.1 audio as well as 2-channel pcm.

I never could understand why everyone went ga ga over ac-3 audio. Must be due the fact that was how 5.1 was presented? (until BD's came along)

[usually_quiet]

I didn't know I could capture as an ac-3 file? I've never been interested in ac-3 for the longest time, or 5.1 audio for that matter. But I think it would be neat to have a BD with 5.1 audio as well as 2-channel pcm.

I never could understand why everyone went ga ga over ac-3 audio. Must be due the fact that was how 5.1 was presented? (until BD's came along)

So, whatever software you are using with the Focusrite 18i6 doesn't provide AC-3 as an option for output, only WAV or MP3. I think you will need to depend on the friend who recommended the Focusrite 18i6 for help. Your buddy apparently knew enough about the Focusrite 18i6 to recommend it to you and presumably he knows something about the software you are using too. I also think you need help with this task to be provided in person.

[Cornucopia]

If you look up ADAT lightpipe, you'll see that the "toslink" like optical cable hardware maybe the same, but it is TOTALLY incompatible to spdif. The only way to go adat->toslink/spdif is a converter box (which would likely just as easily convert to rca spdif). So that port is NO GO.
Also, the rf ac3 goes through a demodulator in either instance: with a processor it additionally decodes the ac3 to multichannel pcm and from there (likely) goes from d->a. Which means you are having another stage/generation of a->d mixed in there (with addional loss/distortion/noise and possible level mismatch).
With the "demodulator" you are only demodulating from rf back to ac3. However, as has been suspected, it does not look like the focusrite hardware (via spdif) nor the scarlett mix app/driver supports passthrough of un-decoded ac3 for straight capture.
It MAY be possible to add a directshow ac3 decode filter in line so that to the scarlett mix app it is seen as 8 channels, but since it only expects/allows >2 channels via adat lightpipe (spdif supports only 2 lpcm channels, and/or ac3/dts streams masquerading as pcm), it is very likely that if you can get it to work at all you would only be able to cap 2 digital channels at a time using THIS hardware. Ultimately, this hardware is both overkill and not optimal for your current use case.

Scott

[clashradio]

I do have a convertor box (adat toslink-to-rca s/pdif). I end up getting distortion on the recording which is not present while capturing. I just chalked it up to thinking it was the cheap Chinese box itself. Plus I'm guessing the output would only be 2-channel if I were to use it from the demodulator to the convertor box.

So you're saying a processor outputs the decoded ac-3 into pcm via the rca's? If that's the case then I should capture as WAV or PCM 16/44 @1536kbps.

I didn't know s/pdif only supports 2 channel Lpcm as I know it supports 5.1. But as you said it's ac-3 5.1 masquerading as pcm.

Ya I was trying to avoid not having to capture the channels separately as three passes (Left Front/Right Front as one track/Left Rear/Right Rear as one track/Center/LFR as one track).

Ideally to avoid the multiple a-d signal conversions and loss, it would be neat if it was possible to capture directly from a demodulator as it's already decoded to digital in 5.1 for an amplifier to receive and kick out the 5.1.

[usually_quiet]

I do have a convertor box (adat toslink-to-rca s/pdif). I end up getting distortion on the recording which is not present while capturing. I just chalked it up to thinking it was the cheap Chinese box itself.

I'm not entirely sure even now that you understand that S/PDIF and ADAT are different, incompatible formats, even if both can be delivered via a Toslink cable. Which ADAT Toslink-to-RCA S/PDIF converter box did you buy?

All the cheap ($10 to $20) Chinese boxes with a Toslink connection and a RCA digital audio connection that I have seen are S/PDIF adapters for situations where one's equipment doesn't have the same type of S/PDIF connection. I don't believe that an ADAT to S/PDIF converter could be a cheap ($10 to $20) device. The conversion is too complex.

I didn't know s/pdif only supports 2 channel Lpcm as I know it supports 5.1. But as you said it's ac-3 5.1 masquerading as pcm.
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.
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Ideally to avoid the multiple a-d signal conversions and loss, it would be neat if it was possible to capture directly from a demodulator as it's already decoded to digital in 5.1 for an amplifier to receive and kick out the 5.1.

Yes, and there are people who have captured 5.1 Dolby Digital/AC3 from Laserdisc using an ac-3 RF demodulator, plus a sound card (or audio interface device) as LPCM, then extracted the 5.1 Dolby Digital/AC3 stream hidden inside.

There are old threads on the subject (mostly not at VideoHelp), but sifting through all the years-old posts to figure out what might work now is hard, confusing work. If you want to do this, you had better hope that someone who knows what sound card (or audio interface device) to buy today and what drivers/software need to be installed today finds your thread.

[Cornucopia]

I agree with usually_quiet. Since ADAT supports 8 ch, on a true converter box there either has to be multiple spdif outs or there has to be a mapping option, or both.

Also, you do realize that of all the releases of LD material, only the last few years included anything that supported AC3 (and even then, not all did). So very often, this kind of decoding will NOT be possible, much less necessary.

Scott

[clashradio]

[QUOTE=usually_quiet I'm not entirely sure even now that you understand that S/PDIF and ADAT are different, incompatible formats, even if both can be delivered via a Toslink cable. Which ADAT Toslink-to-RCA S/PDIF converter box did you buy?

I do know that s/pdif and adat are different and not compatible. I admit I don't understand all of the differences of the two, however between you and Scott I learned that adat is capable of multi-track and s/pdif is not, even though both are digital.

I have a cheap Monoprice conversion box. Mine has optical-in and coax-out. I assumed it was adat-in and s/pidif-out but probably not. I bought it because my soundcard won't accept the toslink signal from LD's or mini-disc etc, but with this box I can send to the coax rca to the soundcard and get signal (that's why I assumed the box was an adat-to- s/pdif converter).

So my card's toslink must be set up for adat and the coax rca is s/pdif.

I've read about guy named "hairyhen" over at the Star Wars Original Trilogy site that extracted the 5.1 mix from the 1993 DC laserdisc.

[usually_quiet]

I have a cheap Monoprice conversion box. Mine has optical-in and coax-out. I assumed it was adat-in and s/pidif-out but probably not. I bought it because my soundcard won't accept the toslink signal from LD's or mini-disc etc, but with this box I can send to the coax rca to the soundcard and get signal (that's why I assumed the box was an adat-to- s/pdif converter).

The Monoprice box that you bought allows connecting an optical (Toslink) S/PDIF device to a coaxial RCA S/PDIF device. They are not bi-directional, meaning the connection on the "In" side must match the connection on the source device and the connection on the "Out" side must match the connection on the destination device. That is why some boxes are described as "Toslink to coax RCA converters" and others are described as "coax RCA to Toslink converters".

So my card's toslink must be set up for adat and the coax rca is s/pdif.

Yes. I told you that in my initial reply to this thread:

The documentation I found indicates that the Focusrite 18i6's optical audio port is an ADAT port, not an S/PDIF port. The Focusrite 18i6 has an RCA S/PDIF port, which is only for stereo audio input, and almost certainly PCM, not Dolby Digital.

I've read about guy named "hairyhen" over at the Star Wars Original Trilogy site that extracted the 5.1 mix from the 1993 DC laserdisc.

You are mistaken. DolbyDigital was not used on LaserDisc until 1999, for the Japanese release of Star Wars: Episode I – The Phantom Menace. [Edit]The final LaserDisc titles were released in 2001, so Scott is correct in saying 5.1 audio was only available on LaserDisc in the last few years of production.

[clashradio]

Yes. I told you that in my initial reply to this thread.

Yes sorry [usually quiet]. I didn't understand that adat and s/pdif were different , that's why I missed your explanation of the Focusrite documentation.

I've read about guy named "hairyhen" over at the Star Wars Original Trilogy site that extracted the 5.1 mix from the 1993 DC laserdisc.

You are mistaken. DolbyDigital was not used on LaserDisc until 1999, for the Japanese release of Star Wars: Episode I – The Phantom Menace.

I know the 1999 Japan Episode 1 had 6.1; are you thinking of that as far as Dolby not being on LD's until 1999? Attached is a pic from my 1989 U.S. Empire Strikes Back LD that says 'dolby surround". That same symbol is on my 1992/93/95 releases of Star Wars as well. I admit I'm a newbie to surround, and I know some of the earlier discs actually said "AC-3" on them. But is Dolby Surround the same as or another name for ac-3?

[usually_quiet]

I know the 1999 Japan Episode 1 had 6.1; are you thinking of that as far as Dolby not being on LD's until 1999? Attached is a pic from my 1989 U.S. Empire Strikes Back LD that says 'dolby surround". That same symbol is on my 1992/93/95 releases of Star Wars as well. I admit I'm a newbie to surround, and I know some of the earlier discs actually said "AC-3" on them. But is Dolby Surround the same as or another name for ac-3?

It appears that DolbySurround is a digital audio format used for home video, which predates Dolby Digital AC3. It can provide either stereo or 2.1 channel audio.

Wikipedia says the following in its Dolby Pro Logic article:

Dolby Surround is the earliest consumer version of Dolby's multichannel analog film sound decoding format Dolby Stereo. It was introduced to the public in 1982 during the time home video recording formats (such as Betamax and VHS) were introducing Stereo and HiFi capability. The term Dolby Surround is used so as not to confuse theater surround (Dolby SR, which has four channels of audio) with home stereo, which has only two. The term also applies to the encoding of material in this sound format. It was capable of decoding Dolby Stereo stereo tracks to 3.0 channels (Left, Right, frequency limited single Back channel).

[Edit]The Wikipedia article for DolbyDigital says that Before 1996, Dolby Digital was marketed as Dolby Surround AC-3, Dolby Stereo Digital, and Dolby SRD. In 1995, the LaserDisc version of Clear and Present Danger featured the first home theater Dolby Digital mix.

So, the first LaserDisc with AC3 sound appeared in 1995. It seems to be 5.1 audio. Now it looks like only discs released in the final 6 years of production could have 5.1 audio.

[Arnold_Layne]

[Attachment 44098 - Click to enlarge]

Yes. I told you that in my initial reply to this thread.

Yes sorry [usually quiet]. I didn't understand that adat and s/pdif were different , that's why I missed your explanation of the Focusrite documentation.

I've read about guy named "hairyhen" over at the Star Wars Original Trilogy site that extracted the 5.1 mix from the 1993 DC laserdisc.

You are mistaken. DolbyDigital was not used on LaserDisc until 1999, for the Japanese release of Star Wars: Episode I – The Phantom Menace.

I know the 1999 Japan Episode 1 had 6.1; are you thinking of that as far as Dolby not being on LD's until 1999? Attached is a pic from my 1989 U.S. Empire Strikes Back LD that says 'dolby surround". That same symbol is on my 1992/93/95 releases of Star Wars as well. I admit I'm a newbie to surround, and I know some of the earlier discs actually said "AC-3" on them. But is Dolby Surround the same as or another name for ac-3?

No. AC-3 (or Dolby Digital) is not the same as Dolby Surround. Dolby Surround is a crude analog surround format used before Dolby Digital and DTS were adopted in home theater systems.

[Cornucopia]

No! You are conflating different, separate things. (somebody beat me to it...)
Dolby Surround is a 4->2->4 (later 5->2->5 etc with DS ProLogic) matrixing scheme. It is architecture-agnostic, so can be used in analog or digital. It has been around since late 70s/early 80s.
Ac3 is only digital (hence "dolby digital"), and and ALL discreet (aka not matrixed), and has only been around since about 1993, and as mentioned only appearing in LD in 99 or later.
Since the middle state of DS is 2 channel, it is very easy & straightforward to put the Lt+Rt signal in the normal stereo/2ch spot, and that is what media companies have done for a long time for media that only supports 2ch: pre-ac3 LD, VHS/SVHS/Beta/8mm/Hi8, VCD. Even some audio-only media use it: CD, LP/45, Cassettes, MD.

To "extract" surround from DS material, just capture the standard 2ch stream, and then tell your player/TV/AVreceiver to decode the stereo as DS. Done.
Or, cap as stereo, then later decode & upmix to 5.1, etc. and save the multitrack as whatever you want: separate channel files, 6ch wav, ac3 5.1, dts, etc, to save the extraction permanently. Note however that this just saves the guessed-at upmix, so it is an approximation of the mix.
In fact, due to the incomplete and destructive nature of matrixing, any DS material will ALWAYS be a higher crosstalk approximation. It will never again be equal to the original multichannel mix.
Another reason why it is only used as a last resort (when no multichannel options are available).

@usually_quiet, wikipedia got a lot of that wrong, or at least only partially right.

Scott

[usually_quiet]

@usually_quiet, wikipedia got a lot of that wrong, or at least only partially right.

That figures. In any case, Dolby Digital /AC3 5.1 audio was only available on LaserDisc releases for a few years near the end.

[clashradio]

Thanks [Cornucopia] & [usually quiet]. It's been a real journey learning the best method for LD to BD, ac-3 audio, adat & s/pdif, Dolby Digital and Dolby Surround. Your info and help has been much appreciated!

Jason