HDMI 7.1 to PCM1794A (or alternatives)

[snoopy33]

Hi,

I currently have a DAC I build comprising of a CM6631A USB to I2S converter and a PCM1794A I2S to analog.

I'm looking to upgrade to four channels and believe USB is not the best way to do it. HDMI or Displayport (over USB-C) are available, so I've began looking at:

Buy Products Online from China Wholesalers at Aliexpress.com

My intention is to send stereo over four channels most of the time, and occasionally downmix 5.1 to 4.0 in Alsa (Linux) and send it over where I'll have a second PCM1794A available for the rear channel.

Can you see any issues with this approach or suggest alternatives?

 

[ubergeeknz]

Why do you believe USB isn't the way to do it?

 

[snoopy33]

Well for a start there's no obvious means to get 4 channels (or more) over USB without resorting to encoding to Dolby Digital 5.1?

 

[dwk123]

Well for a start there's no obvious means to get 4 channels (or more) over USB without resorting to encoding to Dolby Digital 5.1?

Um, there are zillions of multi-channel USB solutions out there. Lots of 7.1 solutions based on Xmos, and then there are all the pro studio solutions that can go up to dozens of channels.

The minidsp usbstreamer would be one to look at if you want I2S out.

 

[chris719]

Well for a start there's no obvious means to get 4 channels (or more) over USB without resorting to encoding to Dolby Digital 5.1?

Not true, as the above poster mentioned.

USB Audio Class 2.0 supports everything you want. The CM6632A will do what you need if you want to stick with a similar chip.

 

[snoopy33]

Ok, other considerations like bandwidth, jitter etc? It just seems that HDMI is better suited to carrying multiple audio channels and at least there's a product (link above) that can do it.

Searching "CM6632A" on aliexpress brings up no products.

minidsp usbstreamer is x3 the cost and re-encodes to TOSLINK. So I'd need another item in the middle to convert this back out to I2S channels.

 

[Sebastian K]

Dear Snoopy,
I had my share of experience with multichannel over HDMI, and while I've yet to find a USB solution, from what I've seen so far I have to agree with the other posters.
HDMI does support 8 ch up to 192/24 (32?) from the beginnings, but the interface is actually for video and transports audio as a by-product.

• I've had crackles during playback due to contact problems.
• I've experienced video driver crashes (these are responsible for the HDMI output).
• The video signals are very high frequency, long cables may degrade output.
• There are measurement results on the web showing jitter well above what the AES has defined as inaudible.

All of the above should be non-issues with an asynchronous UAC 2.0 compatible USB interface, so I'd like to get one too.

Here is one board: XMOS Multichannel high-quality USB to/from I2S/DSD SPDIF PCB - DIYINHK

 

[keilau]

Hi,

I currently have a DAC I build comprising of a CM6631A USB to I2S converter and a PCM1794A I2S to analog.

I'm looking to upgrade to four channels and believe USB is not the best way to do it. HDMI or Displayport (over USB-C) are available, so I've began looking at:

Buy Products Online from China Wholesalers at Aliexpress.com

My intention is to send stereo over four channels most of the time, and occasionally downmix 5.1 to 4.0 in Alsa (Linux) and send it over where I'll have a second PCM1794A available for the rear channel.

Can you see any issues with this approach or suggest alternatives?

I used a similar board and connect the I2S output to a ES9038Q2M
DAC board directly using a 6 conductor cable.
Lusya HDMI/MHL to Dual mode Separation Extraction Audio I2S/DSD/Fiber Coaxial Converter Switch Board T0731 HDMI to I2S/IIS|Switch Caps| | - AliExpress
I am not interested in multi-channel audio. I did it to get SACD output from a Sony Blu-Ray player, UBP-X800 through HDMI.

The 5VDC line on HDMI is sufficient to power the board. No external power supply is needed.