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 Post subject: Re: AC-3 RF specification?
PostPosted: 20 Mar 2021, 18:19 
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signofzeta wrote:
If the whole thing is based on a proprietary chip long out of production that we don’t have real documentation on then it’s as far from open source as I can imagine.

And are there seriously pirate copies of this useless chip? That seems crazy.


I don’t know, but if I tried certain IC sellers in China for the odd single example on EBay, chances are that I’d get a relabelled non-working chip with fresh dodgy looking laser markings.

The cool thing is that the service manual for the Pioneer RFD-1, or the Denon AVD-2000 or some other device is readily available. The chip needs some analog frontend stuff, some glue logic, a crystal and a RAM chip. No need for a microcontroller with firmware to make it all work. It’s really self-contained that way. I’ve seen more complicated devices, so there’s nothing to fear here in terms of complexity. Lots of stuff is explained via the service manual for the RFD-1, something else might be given away in the Yamaha, Kenwood, or Denon PDF for instance.
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 Post subject: Re: AC-3 RF specification?
PostPosted: 20 Mar 2021, 18:35 
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Yeah, the chip pretty much is the circuit. There was little to no firmware in any consumer level gear back then.

I would not assume any pirate copies exist. AC-3 decoding for Laserdisc was only relevant for five years, if that, and the installed user base was a few hundred thousand. The incentive to copy something so worthless seems ...below zero. Even pirate LDs themselves are rare because there just want a market for it.
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 Post subject: Re: AC-3 RF specification?
PostPosted: 29 Jun 2021, 14:12 
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mikechambers wrote:
I came into this forum to basically post this exact thread.

I was hoping to find some information on the AC3 RF signal. Like the frequency it operates on, etc.

I'm an embedded firmware developer, and I wanted to look into building my own demodulator with a few cheap parts like say an AVR (Not sure if they're fast enough -- might need to go ARM) plus some RF and SPDIF modules. The problem is I just can't seem to find the required technical documentation on the AC3 RF signal itself.

In theory, I should be able to convert the RF signal into a bitstream and send it out over SPDIF relatively easily. In theory. I'll see if theory matches up with reality if I can get my hands on specs. :lol:

If I'm able to come up with a solution, I'd be happy to share the information and even source code with others who could build their own. Hopefully with just a dirt-cheap Arduino board and a couple other bits. I could utterly fail, as RF isn't one of my areas of expertise, but I'd at least like to give it a try.

$200+ on eBay just to get AC3 surround from a Laserdisc is insane.

I'm wondering if the details are too well-kept of a secret to pull this off.


If you find anything about "software decoding" AC3-RF that would also be very helpful for ld-decode. See: https://github.com/happycube/ld-decode/issues/622
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 Post subject: Re: AC-3 RF specification?
PostPosted: 02 Dec 2021, 16:36 
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Well, there aren't any specs, but I spent some time the last couple of weeks to figure out how it works: https://bitbucket.org/staffanulfberg/ld ... rc/master/

I basically sampled the signals going into and out from my AC3RF decoder and wrote code to demodulate the bits going in, and also to decode the spdif stream going out. It took some crunching to figure out how it all fits together but it's not a mystery anymore:)
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 Post subject: Re: AC-3 RF specification?
PostPosted: 02 Dec 2021, 21:39 
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This is a significant moment in LD history. Fantastic staffanu!
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 Post subject: Re: AC-3 RF specification?
PostPosted: 02 Dec 2021, 22:08 
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Well I sold my decoder just in time 8-)
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 Post subject: Re: AC-3 RF specification?
PostPosted: 03 Dec 2021, 02:22 
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staffanu wrote:
It took some crunching to figure out how it all fits together but it's not a mystery anymore:)


I read the notes and... maybe I understood 10% of them! ^_^;

But it sounds like a great step ahead. :clap:
Sadly too late to have it added to a Radiance by Lumagen!

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 Post subject: Re: AC-3 RF specification?
PostPosted: 03 Dec 2021, 02:23 
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rein-o wrote:
Well I sold my decoder just in time 8-)


FPGAs are not cheap and hard to come by these days with regular price hikes.
It might not cost LESS to do it custom than buying a 2nd hand demod.

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 Post subject: Re: AC-3 RF specification?
PostPosted: 10 Dec 2021, 15:02 
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Just an fyi, there was a variant of the demodulator chip. The Sony ep9es uses chip PD4606a as did Rotel RDA-980. This chip is still available it seems from a google search, haven't tracked down a datasheet yet. I also didn't see the service manual for the ep9es in the archive so I'll submit it, but the Rotel one is already there and shows this chip for anyone interested.

ldfan wrote:

Also, I really doubt your friend would be able to make his own Demodulator since the main requirement is the Pioneer, PM-4007, DSP chip that is the heart of the decoding process. This chip is essentially not available @ this point in time.

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 Post subject: Re: AC-3 RF specification?
PostPosted: 09 Dec 2022, 23:41 
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Thanks to the legwork by staffanu my son and I have managed to include this in ld-decode

https://github.com/happycube/ld-decode/pull/808
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 Post subject: Re: AC-3 RF specification?
PostPosted: 10 Dec 2022, 17:10 
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This is a gigantic leap forward, thank you to all involved.

Also, I love it when the nay-sayers are proved wrong. Let the people saying it can't be done get out of the way of the people GETTING it done.

We all benefit from the knowledge and tenacity of a few people here making amazing homebrew projects to keep LD alive indefinitely.

From 3D printed parts to AC3 mod circuits to DdD + LD Decode and now this. Simply amazing.

I know it is asked a lot and always laughed at but I don't put it past someone finding a way to spin these things up to speed in a new player or to burn a CDV.

Anything is possible. Only time and determination are going to stop it.
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