Quadraphonic to HDMI?

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JediJoker

2K Club - QQ Super Nova
Joined
Jul 13, 2015
Messages
2,630
Location
Portland, OR, USA
I want to be able to listen to vintage quadraphonic sources with all the benefits of my Marantz SR6014's room correction. Obviously, the 7.1 analog inputs are pass-through only, as the receiver would cost far more if implementing eight channels of ADC. It would be possible to use the MiniDSP DDRC-88A with the -88BM plugin added as a middleman, but that would mean setting up a whole new room correction profile on a separate piece of hardware rather than using what my receiver already has built-in. Plus, I'd be paying for double the channels of ADC that I actually need, and eight superfluous channels of DAC.

The device I have in mind would have at least two sets of 4 x RCA analog inputs (FL/FR/SL/SR) for quadraphonic line sources, internally switched in the analog domain so as to need only four channels of ADC, and a single HDMI output sending the four channels within a 7.1 LPCM stream (correctly assigned). It would only need to output a full screen black (or, heck, a static or moving logo) video signal accompanying the audio to meet HDMI specifications. Considering the less than stellar signal-to-noise ratio and frequency response found on consumer quadraphonic tapes and vinyl, basic 16-bit/48kHz ADCs would suffice. The anti-aliasing filters could start as low as 16kHz, allowing for a gentle slope to -96dB at 24kHz for zero aliasing and minimal phase shift artifacts in the audible band. Up the sampling frequency to 96kHz and one could achieve even better phase coherence.

Seems like a relatively simple device, no? I am not technically apt or electrically knowledgable enough to actually implement my ideas, but intuitively, they seem trivial. I think the most complicated circuits would be the filters and HDMI components. I know I'm not the only one who would find such a device useful, especially as fewer and fewer receivers include multichannel analog inputs of any kind.
 
Oh man, we hashed this out pretty good when I was looking for the same thing here: 4x RCA to HDMI for Quadraphonic Record Player / Quad Demodulator to Use On HDMI Only System

HDMI is not a friend of analog RCA, it sounds like an easy setup but there's apparently licensing costs that would hinder any development and I'm not entirely sure but they do have 2xRCA to HDMI I've seen that I'm curious if you take 2 of them to see if you could splice them together and see if it would work.

The other idea I had was if you just have a demodulator to run the 4 RCA outputs to an older analog receiver with 5.1 or 7.1 or more inputs and just leave the unneeded inputs alone. "Should work" but I don't have one to test with and rumor has it that even if it works you probably wouldn't be able to output from it over the "HDMI out" to your already existing more modern receiver as HDMI spec would block it over DRM software in the receiver. Again, I have not testing this theory but I did go out to search for receivers with 5.1 RCA in and up with HDMI out and they are all over the place used, but newer models with this cost a small fortune, in my case only a few hundred more than the fortune I paid for my shiny new Atmos receiver last year with no surround RCA input!

What I wound up doing was spending about 2 days to put together a speaker switch between my home theater amp and a 70's quad amp, it works pretty good so far. Images in the link above.

Good luck on all this, please read through the link above and check out where many in the community came out to try and assist. It's a pretty awesome bunch who came out to try and tackle this. Please let us know any solution you may have found!
 
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