Hi
I have an idea of creating an hdmi input for my diy dac. Basically give my dac a bit of home theater functionality. Does anyone know of an hdmi input circuit with passthrough and digital audio out?
There are many hdmi switches with digital audio out that could be hacked but a dedicated pcb would be a cleaner solution.
I have an idea of creating an hdmi input for my diy dac. Basically give my dac a bit of home theater functionality. Does anyone know of an hdmi input circuit with passthrough and digital audio out?
There are many hdmi switches with digital audio out that could be hacked but a dedicated pcb would be a cleaner solution.
I don't think you'll find much beyond what you've already discovered. The main problem with a product like this is copy protection requirements. HDMI data is encrypted, and it's not allowed to make a box that allows this data to "escape" in digital form (other than more encrypted HDMI) unless it's been downmixed/ downsampled/ degraded in some way, as is generally the case with the digital outs you see on the HDMI switches.
Analog output is another matter entirely. The miniDSP nanoAVR HDA, for just one example, has HDMI in/passthrough, plus 8 channels of analog RCA audio out - with some powerful DSP in between. Uses the AKM AK4440 DAC IC, which of course is no audiophile's darling, but doesn't suck either.
-- Jim
Thank you that was a brilliant explanation!
That miniDSP has exactly the functionality i want to achieve. So getting the digital audio out and into a dac is possible. That leaves just the problem with encryption?
HDMI Splitter is also a Decrypter | Hackaday
The downgraded audio is really a dissapointment. I guess it is a licensing issue? I read somewhere that the hdmi license is really expensive.
That miniDSP has exactly the functionality i want to achieve. So getting the digital audio out and into a dac is possible. That leaves just the problem with encryption?
HDMI Splitter is also a Decrypter | Hackaday
You're welcome! Happy to help.
I'm not sure if it's a licensing issue so much as the fact that all this yummy hi-res digital audio/ video is simply not allowed to exist anywhere "outside the box" unless it's encrypted, or downgraded to one of the "legacy" digital formats. However:
To elaborate a bit:
miniDSP recently developed a nice (to me, anyway) little 8-channel I2S DAC board, which they then proceeded to "marry" to several of their little digital boxes. The nanoAVR HDA for example is descended from the original (HDMI-only) nanoAVR HD, with the DAC board added (and new firmware) in a slightly larger box. The fun part of course is that the original digital board has a nice little I2S header on it (I2S Master), which is used to feed the DAC board in the HDA version, and is of course unencrypted.
So if one were sufficiently proficient in I2S, one could theoretically substitute a different DAC (or several) I suppose. A few caveats so I can sleep tonight:
1. I haven't specifically tried this (yet)
2. This would of course void the warranty on your little $250USD box
3. The company will not support discussions on hacking their products
4. You didn't hear any of this from me.
5. If it matters, be advised that the nanoAVR HD (both versions) resamples everything to 96 KHz. It's a nice high-quality resample (I certainly can't hear it), but it can't be bypassed. The other one, nanoAVR DL, includes Dirac Live processing instead of the user-configurable DSP, and resamples everything to 48 KHz.
Have fun, and let us know how/if you get on.
Wow! This looks like an interesting read, thanks.
-- Jim
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Sorry for any confusion. I2S & HDMI audio are 2 separate entities. For example, the I2S data available on the aforementioned header pins is just pure digital audio in serial form, with clock lines & data lines & stuff. It has been extracted (& decrypted) from the original HDMI audio stream, and no longer has anything to do with HDMI, which of course is a good thing. I don't think the I2S specification even has a provision for any type of encryption.
[EDIT] One other thing: You're not likely to find any I2S anywhere inside something like an HDMI switch or splitter, unfortunately. Such boxes have no need to separate the audio from the HDMI stream, except perhaps to feed the odd coax/toslink/analog stereo output; and in those cases, any I2S signals will be both hard to find and probably already downgraded to comply with the required compliances. The miniDSP stuff is an exception, since it's main purpose is high-quality audio processing (the HDMI output is simply a passthrough for video). That's why there happens to be some serious I2S digital audio lurking inside this product and not the others.
Here's a pretty good description of I2S. Put the kettle on.
-- Jim
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Thank you!
I will read that.
I actually spent the night researching hdmi, i2s, splitters and receivers
From what ive seen so far at least some hdmi receiver chips have spdif and i2s out pins. This appears to be the case for most chips used in hdmi de-embedder / switches / splitters where you get spdif out.
Im hoping that the receiver chips do not downgrade the audio. At least there has to be some chips that dont as the miniDSP manages to get high quality out.
I havnt seen any splitter/switch with i2s out, only spdif, so the pins, if present, should be free and begging to be tapped into
I will read that.
I actually spent the night researching hdmi, i2s, splitters and receivers
From what ive seen so far at least some hdmi receiver chips have spdif and i2s out pins. This appears to be the case for most chips used in hdmi de-embedder / switches / splitters where you get spdif out.
Im hoping that the receiver chips do not downgrade the audio. At least there has to be some chips that dont as the miniDSP manages to get high quality out.
I havnt seen any splitter/switch with i2s out, only spdif, so the pins, if present, should be free and begging to be tapped into
That is a good point. Perhaps the receiver chip is just outputting the type of audio it's been programmed to output by the microcontroller on the board. If this is the case, a hack similar to the one you linked to might be possible. For myself, I'm immensely enjoying the added DSP features of the nanoAVR stuff. If you're not tired of reading, here's what I've been doing with it:
The shorter, summarized version
The longer, Jim-slowly-figures-stuff-out version
Enjoy your hackery, wherever it may lead.
-- Jim
I would have loved to see that rig
Well, it doesn't look like much (especially in my crappy little apartment), but it sure sounds nice!
-- Jim
Most "full featured" version of this that I know of involves using an Oppo BDP-93 or BDP-103 with a Vanity HD board. By "full featured" I mean it completely decodes high resolution DTS and DD. It works really well thanks to the modular construction of the Oppo. The multi-channel digital output board gets fed all 7.1 signals already decrypted from another board, so it's rather straight forward to buffer and re-transmit them. There are a number of very cool options, including femto clock and AES ouptuts, and I think even a DsD over S/PDIF is an option.
Another Oppo BluRay player option that is useful to us is the ability to take HDMI input directly, or via the Audio Return Channel (ARC), which makes it easy to keep your TV as your HDMI switch.
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