Dump everything you know about HDMI eARC here

[djtwxj]

thanks
it not identify support dolby atmos

check this one, support dolby atmos

https://www.aliexpress.com/item/1005008762182617.html

 

[MCH]

thanks
it not identify support dolby atmos

check this one, support dolby atmos

https://www.aliexpress.com/item/1005008762182617.html

Thanks for sharing. If you buy one, would you mind posting pictures of the insides?
Thanks

 

[stigger]

From the link above:

The Navceker HDMI-compatible Switch supports LPCM 7.1CH, Dolby True-HD, DTS-HD, AC 3, DTS, DSD, Dolby Digital Plus, and Dolby Atmos audio formats, but cannot decode these audio formats

So unless I'm missing something, it won't give any benefits over the extractor mentioned in the first post.

 

[djtwxj]

What's the audio format from I2S?

the HDMI input audio format is dolby truehd + atmos + mat
the i2s audio format is also dolby truehd + atmos +mat , if so how to remove mat and get dolby truehd + atmos
or dolby truehd + atmos , if so we can decode it to pcm 9.1.6
or dolby truehd , if so can only decode to 7.1

 

[djtwxj]

can help record samples from the i2s port with hdmi in dobly atmos audio format?

 

[phofman]

IIUC an eARC -> I2S extractor capable of all formats would require an 8ch I2S (just like the eARC extractor in RK3588 SoC). Then it's up to the I2S receiver how it treats the incoming data streams. The transmission could be TDM too (i.e. bit clock running at 8ch * 192kHz * 24bits = 36.864 MHz = maximum eARC bitrate of 37Mbps).

 

[djtwxj]

The bitstream audio from HDMI in i think is not 8 ch, it should be 2 ch with dolby truehd atmos with mat?

 

[phofman]

PCM/LPCM has channels. Non-PCM streams are just bitstreams (which yield channels after decoding to PCM) which need to be stuffed somehow into the channel-oriented transmission links.

Look at this nice eARC description for eARC transmitter/receiver chips SiI9438/SiI9437 https://www.digikey.pl/Site/Global/...nfRfVFOwB8POxLizNVoEQqvsGZrDlyLu_j9637GTFlV-S and their data brief https://www.latticesemi.com/-/media...aSheets/SiI-DB-02013-B.ashx?document_id=52242 - the I/O interfaces are 4-lane (= 8ch) I2S.

 

[djtwxj]

No, not disconnecting anything, I even left the resistors in place and simply soldered the wires to them.

Hi, would u mind upload some pictures of your setup of the two boards?

 

[stigger]

Hi, would u mind upload some pictures of your setup of the two boards?

Sorry, I didn't make any photos back then, and now everything's assembled, so there is not much to see. But connecting the lanes is quite straightforward, as long as you have a datasheet for one of the chips (was linked somewhere in this thread) and a digital multimeter to test the connections.

 

[danstahl]

I'd like to DIY an hdmi earc source from a computer. This way I can directly send audio to a sink (eg minidsp or soundbar) without going through an extractor or a TV.

My thought is that I could use a tv hdmi board and hook it up to a rpi, but I haven't had much luck finding tv hdmi boards. Any pointers to where I could find such a device?

 

[phofman]

I'd like to DIY an hdmi earc source from a computer.

Would regular HDMI multichannel audio suffice? Much easier than HDMI earc source.

 

[danstahl]

Indeed, that's trivial . I have a minidsp flex htx and a orei earc extractor, it would be nice to remove the earc extractor and go straight from the computer.

 

[phofman]

Well, an earc-only DSP would be a big limitation here

 

[djtwxj]

no more update on this ?

 

[MCH]

no more update on this ?

Well, @stigger managed to hack the board in post #1 and bring the multichannel signal to a raspberry pi successfully. I have not found any other eARC device that exposes the i2s pins in a header and the evaluation boards remain expensive, so probably something like the one in post #1 is still your best option.
The information about eARC remains very scarce and I am not aware of any hack or anyone making it work on any SBC, so yeah, nothing new under the sun I guess...

 

[phofman]

Details of eARC are in HDMI 2.1 specs, e.g. https://dokumen.pub/hdmi-specificat...ia-interface-specification-v21-v21nbsped.html - from page 293

Quoting from that document:

The eARC TX shall not send audio other than Basic Audio unless the eARC Capabilities Data Structure indicates support
of other audio formats and sample rates. The eARC TX shall only send Basic Audio or audio that the eARC RX indicates
it supports.

That means eARC RX controls what the TX can send. It's logical, technically correct, but it means IMO a proper eARC (or ARC) support requires being able to control the eARC receiver - what audio capabilities the eARC RX sends in the capabilities data structure. Maybe some hard-coded default (8ch, ...) is being used in the standalone eARC receivers.

 

[stigger]

I'm still very happy with my hacky solution, by the way. Setting it up was not easy, but once configured it seems to be stable enough. Kodi on the Ugoos box decodes the sound to PCM and downmixes to 3.1, TV passes it through, then through the eARC/RPi/CamillaDSP/UltraLite-mk5 chain. Kodi allows to set a negative audio delay, so I don't have to worry about FIR latency.

The only limiting factor of this setup is inability to use the TV as a content source: you always need an external box with configurable negative audio delay. Fire TV stick works well too.

 

[nullpointerninja]

Hi stigger, have you measured the latency without any FIR filters active? I’m wondering if it might be useful for real time capture of multichannel LPCM but I don’t know if the inherent latency of capturing via I2S might defeat the purpose without even considering any filtering at all.

Thanks!

 

[stigger]

I did not, and if I were to measure the latency without filtering, I'm not sure if that would be of any use, because measuring reliably is quite difficult and there are too many factors influencing the result:
- my TV is A95L, which is known to have a higher than average video processing latency, requiring to manually set an additional delay on the A/V receiver
- eARC has a mandatory lipsyncing protocol. The TV allows to enable or disable A/V syncing, and I'm not really sure if that affects anything with this eARC extractor device
- my Kodi setup sometimes has lipsync quirks as well, restarting the playback helps