Laserdisc PCM Capture Guide

[zoidberg]

If you have a multimeter you should be able to check if you're getting any output at all from the RF jack. I think the RF signal has a higher voltage than regular audio jacks

[Dr. Cooper]

Currently not, perhaps one can be borrowed early next week.

However, are there any settings that may have to be changed? Right now it's set for bitperfect captures as in the first post. Perhaps the driver-settings that have to be switched to analog, sample rates that have to be changed or whatever?

[zoidberg]

Well yes, it's an analogue FM signal so you'll want to capture with an analogue-to-digital input

[Dr. Cooper]

OK, so the input in the driver-settings should be switched to analog. But that still didn't solve the problem. Anything else that could be changed for now?

Edit: Just tried to find out what happens if the AC3-RF-out is connected to the Cinch-input on a TV. I assume it should be creating some weird scratching noise like a radio on a dead frequency or something like that. But nothing at all, so probably it really is an issue with the hardware on the LD-player and not just a software-issue in the capture-chain?

[zoidberg]

I haven't read anything in the ld-decode documentation that mentions capturing the RF as 16-bit wav. As far as I can tell it works from the raw ld-decode capture which would be captured with a custom domesday board, this is in the MHz range so more like a video signal (hence the custom board)

[Dr. Cooper]

But anyway there should be any sort of noise coming from the AC3-RF-output when an AC3-LD is played and not just silence - or am I totally wrong here?

[zoidberg]

I'm not sure if it's audible in it's raw form. You would probably need an oscilloscope to see the signal.

[bronan]

OK, so the input in the driver-settings should be switched to analog. But that still didn't solve the problem. Anything else that could be changed for now?

You can try capturing a regular LD with analog audio from the standard outs to make sure your recording setup is working correctly.

[Dr. Cooper]

You can try capturing a regular LD with analog audio from the standard outs to make sure your recording setup is working correctly.

That works perfectly fine, it's just the AC3-RF-out where nothing at all can be heard.

[zoidberg]

Reading into it a bit more and it's normal to not be able to 'hear' anything from the AC-3 RF out, it's a radio signal in the megaherz range.

It does seem to me to be the case that you will need the Domesday duplicator device/capture chain to extract this AC-3 signal without a demodulator. Considering the process uses hundreds of GB per hour of raw capture, I have to say it's probably easier to get ahold of a demodulator unit, they do occasionally come up at a reasonable price. There is also something called SDR (software defined radio), maybe the methods used there could be applied to this (QPSK is a common digital modulation method nowadays)