Multichannel audio on a Pi will get a whole lot easier and cheaper!

[charlielaub]

It's alive! Haven't done tons of listening but I'm getting clean output on all channels. Example FFT from ch 3 shown below as captured by a MOTU Ultralite Mk5.

Thanks for all your help @phofman!

Now to try some I2S input.

Michael

I'm a little confused about why you would bother with the I2S interface when you have a USB MOTU ULmk5 with 10 analog output channels and that (supposedly) works perfectly with CDSP... Was there a reason for going that route?

 

[gordoste]

I'm a little confused about why you would bother with the I2S interface when you have a USB MOTU ULmk5 with 10 analog output channels and that (supposedly) works perfectly with CDSP... Was there a reason for going that route?

He said before he was looking at using the I2S input to bring surround sound into CDSP. I assume this would be much cheaper.

 

[mdsimon2]

I'm a little confused about why you would bother with the I2S interface when you have a USB MOTU ULmk5 with 10 analog output channels and that (supposedly) works perfectly with CDSP... Was there a reason for going that route?

I am not personally very interested in multichannel I2S output but I figured others might be (although I always love to tinker). And as a first step in multichannel I2S with the RPi I figured multichannel output would have less variables as I already have a McFIFO / McDualXO + 8 channel AES output device sitting on the shelf that I know works with multichannel I2S input.

I am mostly interested in the potential for multichannel I2S input from a 7.1 HDMI to I2S extractor like this -> https://www.aliexpress.us/item/2251832845605595.html. An Apple TV + HDMI to I2S extractor + RPi 5 running CamillaDSP + multichannel USB DAC (like the UL Mk5) is a very interesting AVR replacement setup to me.

Michael

 

[charlielaub]

He said before he was looking at using the I2S input to bring surround sound into CDSP. I assume this would be much cheaper.

The MOTU also has 8 analog inputs, plus toslink and coax spdif inputs...

 

[mdsimon2]

The MOTU also has 8 analog inputs, plus toslink and coax spdif inputs...

Which would be great if I had an AVR, but I don't.

I do have an Apple TV, several multichannel DACs and a 7.1 HDMI to I2S extractor. A RPi 5 is a small investment to see if I can make it all work.

Michael

 

[charlielaub]

I am not personally very interested in multichannel I2S output but I figured others might be (although I always love to tinker). And as a first step in multichannel I2S with the RPi I figured multichannel output would have less variables as I already have a McFIFO / McDualXO + 8 channel AES output device sitting on the shelf that I know works with multichannel I2S input.

I am mostly interested in the potential for multichannel I2S input from a 7.1 HDMI to I2S extractor like this -> https://www.aliexpress.us/item/2251832845605595.html. An Apple TV + HDMI to I2S extractor + RPi 5 running CamillaDSP + multichannel USB DAC (like the UL Mk5) is a very interesting AVR replacement setup to me.

Michael

OK, I see. A bit of a hardware mish mash but you are home cooking an interesting and challenging project. I used to try these things with the Pi, with HDMI audio extractor dongles or HATs, but not with input.

Are you planning to process audio from home theater (movies)? If so what sort of latency do you expect?

 

[mdsimon2]

OK, I see. A bit of a hardware mish mash but you are home cooking an interesting and challenging project. I used to try these things with the Pi, with HDMI audio extractor dongles or HATs, but not with input.

Are you planning to process audio from home theater (movies)? If so what sort of latency do you expect?

Yes, 5.1/7.1 audio from streaming services

My hope would be to clock sync the UL Mk5 to HDMI extractor via the TOSLINK output of the HDMI extractor. This should allow me to avoid resampling in CamillaDSP. In synchronous systems I've been able to successfully use a chunk size of 256 and 48 kHz which gives around 15 ms latency with the UL Mk5, although I might need to increase chunk size. Long story short, under 30 ms.

Michael

 

[mdsimon2]

Congrats. Now you know we will be expecting a titorial

Very brief tutorial assuming you know your way around a Pi / Linux.

1) Install raspberry pi os lite 64 bit using raspberry pi imager.

2) Clone 6.7 kernel.

git clone --depth=1 --branch rpi-6.7.y https://github.com/raspberrypi/linux

3) Configure kernel

cd linux
KERNEL=kernel_2712
make bcm2712_defconfig

4) Modify kernel to use all i2s inputs / outputs.

nano ~/linux/arch/arm/boot/dts/broadcom/rp1.dtsi

rp1_i2s0_18_21: rp1_i2s0_18_21 {
   function = "i2s0";
   pins = "gpio18", "gpio19", "gpio20", "gpio22", "gpio24", "gpio26", "gpio21", "gpio23", "gpio25",  "gpio27";
   bias-disable;
};

rp1_i2s1_18_21: rp1_i2s1_18_21 {
    function = "i2s1";
    pins = "gpio18", "gpio19", "gpio20", "gpio22", "gpio24", "gpio26", "gpio21", "gpio23", "gpio25",  "gpio27";
    bias-disable;
};

5) Compile modified kernel. This will take around 45 minutes on a raspberry pi 5.

make -j4 Image.gz modules dtbs
sudo make modules_install
sudo cp arch/arm64/boot/dts/broadcom/*.dtb /boot/firmware/
sudo cp arch/arm64/boot/dts/overlays/*.dtb* /boot/firmware/overlays/
sudo cp arch/arm64/boot/dts/overlays/README /boot/firmware/overlays/
sudo cp arch/arm64/boot/Image.gz /boot/firmware/kernel_2712.img
sudo reboot

6) Clone RaspberryPi_I2S_Master

git clone https://github.com/AkiyukiOkayasu/RaspberryPi_I2S_Master

7) Compile RaspberryPi_I2S_Master and copy to /boot/overlays

cd RaspberryPi_I2S_Master
dtc -@ -H epapr -O dtb -o i2smaster.dtbo -Wno-unit_address_vs_reg i2smaster.dts
sudo cp i2smaster.dtbo /boot/overlays

8) Modify /boot/config.txt to use I2S.

sudo nano /boot/config.txt

#dtparam=i2c_arm=on
dtparam=i2s=on
#dtparam=spi=on
dtoverlay=i2smaster

9) Reboot pi.

sudo reboot

10) Setup CamillaDSP configuration.

I used playback device as hw:I2Smaster, S32LE format and 8 channels.

----

Some good references where I gathered all this info, again thanks to @phofman.

Raspberry Pi Documentation - The Linux kernel

The official documentation for Raspberry Pi computers and microcontrollers

www.raspberrypi.com

GitHub - AkiyukiOkayasu/RaspberryPi_I2S_Master: General I2S master I/O device tree overlay for Raspberry Pi.

General I2S master I/O device tree overlay for Raspberry Pi. - AkiyukiOkayasu/RaspberryPi_I2S_Master

github.com

RPi5 I2S details? - Raspberry Pi Forums

forums.raspberrypi.com

https://datasheets.raspberrypi.com/rp1/rp1-peripherals.pdf

----
Pin Mapping
GPIO 18: BLCK/SCLK
GPIO 19: WS/LRCLK
GPIO 20: I2S data IN 0
GPIO 22: I2S data IN 1
GPIO 24: I2S data IN 2
GPIO 26: I2S data IN 3
GPIO 21: I2S data OUT 0
GPIO 23: I2S data OUT 1
GPIO 25: I2S data OUT 2
GPIO 27: I2S data OUT 3
----

Michael

 

[mdsimon2]

Got the HDMI to I2S extractor working as an input in to the RPi5 running in slave mode!

Followed instructions from here -> https://github.com/AkiyukiOkayasu/RaspberryPi_I2S_Slave/tree/master. I needed to change all instances of <&i2s> to <&i2s_clk_consumer> as described here -> Re: Simple-audio-card I2s audio issues (bookworm). My CamillaDSP capture device is hw:GenericStereoAu,1 using 8 channels of S32LE.

Now getting 8 channels of perfect 24 bit audio at 48 kHz over HDMI from a MacBook Pro in to the RPi5 running CamillaDSP. Using the UL Mk5 as a playback device clocked via optical from the extractor. Currently using 512 chunk size in CamillaDSP and buffer level seems pretty stable but I'll need to listen for longer to see if I get buffer under runs.

Only oddity so far is channels 3 (center) and 4 (subwoofer) seem to swapped in the extractor, although this could also be something to do with routing from my Mac. This seems persistent through CamillaDSP restarts.

Looking forward to doing some testing with an Apple TV tomorrow.

Michael

 

[MCH]

I think this is excellent news for the DIY folks. With one of these Explore hdmi transceiver chips similar to the one Michael uses but the ones that don't need MCU (ie. EP92A3E), and a multichannel dac, one could now assemble a hat that takes HDMI, sends it to the pi for DSP and outputs more than decent up to 8 channels analog in a very compact cost effective device.
I have in a drawer the HDMI side reverse engineered from one of these extractors. It is a lot of parts, but only one IC and no programming involved.
If this works with stuff like netflix, it will make a very cool project (crossing fingers for no channel swapping this time )

 

[phofman]

@mdsimon2 : Maybe you could try an overlay like this which only changes the pins param of the rp1_i2s0/1_18_21 nodes (untested):

//Device tree overlay for 8ch RP1
/dts-v1/;
/plugin/;

/ {
    fragment@0 {
        target = <&rp1_i2s0_18_21>;
        __overlay__ {
            pins = "gpio18", "gpio19", "gpio20", "gpio22", "gpio24", "gpio26", "gpio21", "gpio23", "gpio25",  "gpio27";
        };
    };

    fragment@1 {
        target = <&rp1_i2s1_18_21>;
        __overlay__ {
            pins = "gpio18", "gpio19", "gpio20", "gpio22", "gpio24", "gpio26", "gpio21", "gpio23", "gpio25",  "gpio27";
        };
    };
};

A very handy command is listing the whole tree, with overlays applied (the symbols are at the end):

dtc -I fs /sys/firmware/devicetree/base

 

[mdsimon2]

Apologize for my ignorance, should I try that overlay on an unmodified kernel?

Is that a replacement of a portion of the i2smaster.dts / genericstereoaudiocodec.dts or should it be used on it's own?

Michael

 

[phofman]

That should work (provided the overlay is correct) for the stock RPi kernel. Just put it into another DTS file, compile to dtbo, and add to config.txt https://raspberrypi.stackexchange.com/a/40220

 

[charlielaub]

Got the HDMI to I2S extractor working as an input in to the RPi5 running in slave mode!

Followed instructions from here -> https://github.com/AkiyukiOkayasu/RaspberryPi_I2S_Slave/tree/master. I needed to change all instances of <&i2s> to <&i2s_clk_consumer> as described here -> Re: Simple-audio-card I2s audio issues (bookworm). My CamillaDSP capture device is hw:GenericStereoAu,1 using 8 channels of S32LE.

Now getting 8 channels of perfect 24 bit audio at 48 kHz over HDMI from a MacBook Pro in to the RPi5 running CamillaDSP. Using the UL Mk5 as a playback device clocked via optical from the extractor. Currently using 512 chunk size in CamillaDSP and buffer level seems pretty stable but I'll need to listen for longer to see if I get buffer under runs.

Only oddity so far is channels 3 (center) and 4 (subwoofer) seem to swapped in the extractor, although this could also be something to do with routing from my Mac. This seems persistent through CamillaDSP restarts.

Looking forward to doing some testing with an Apple TV tomorrow.

Michael

Are doing, or plan to do, any processing within CamillaDSP or is CDSP just a tool to connect the I2S input to the ULmk5 output while maintaining sync?

 

[mdsimon2]

Are doing, or plan to do, any processing within CamillaDSP or is CDSP just a tool to connect the I2S input to the ULmk5 output while maintaining sync?

Yes, using CamillaDSP to implement processing. This is a bit of a far out project without any concrete plans but the intent would be to use DIY active speakers for at least L + C + R.

Michael

 

[mdsimon2]

That should work (provided the overlay is correct) for the stock RPi kernel. Just put it into another DTS file, compile to dtbo, and add to config.txt https://raspberrypi.stackexchange.com/a/40220

Made a file called 8chi2s.dts with your code snippet and used the command "dtc -@ -H epapr -O dtb -o 8chi2s.dtbo -Wno-unit_address_vs_reg 8chi2s.dts" to compile which is just copy / paste from RaspberryPi_I2S_Master example. Copied the dbto to /boot/overlays and added dtoverlay=8chi2s to /boot/config.txt.

I don't see any difference when running "dtc -I fs /sys/firmware/devicetree/base" when the dtoverlay is specified or not (files attached for reference).

Michael

 

[mdsimon2]

Did some listening with an Apple TV HD, seems well behaved and am getting 5.1 PCM.

Haven't found anything that will send 7.1 from the Apple TV, it will either report "5.1" or "Dolby Atmos" but I never see anything on the rear channels. Although from some googling it doesn't seem like much if any non-atmos 7.1 is available on streaming services and even if it is technically 7.1 there is rarely any content on the rear channels. If you know of a 7.1 example available streaming let me know.

Center is coming through on channel 4 which seems to confirm the center / subwoofer channel swapping is occurring in the extractor.

Michael

 

[phofman]

I don't see any difference when running "dtc -I fs /sys/firmware/devicetree/base" when the dtoverlay is specified or not (files attached for reference).

IMO the 8ch pins were applied correctly, sure there is a difference:

pavel@hp:~$ diff overlay_*
1320c1320
<             rsts = <0x20>;
---
>             rsts = <0x1020>;
2765c2765
<                         pins = "gpio18\0gpio19\0gpio20\0gpio21";
---
>                         pins = "gpio18\0gpio19\0gpio20\0gpio22\0gpio24\0gpio26\0gpio21\0gpio23\0gpio25\0gpio27";
3083c3083
<                         pins = "gpio18\0gpio19\0gpio20\0gpio21";
---
>                         pins = "gpio18\0gpio19\0gpio20\0gpio22\0gpio24\0gpio26\0gpio21\0gpio23\0gpio25\0gpio27";

But I do not see any master/slave card changes in those dumps, no spdif or capture_link string, etc, all i2s configs have status disabled. Debugging e.g. https://forums.raspberrypi.com/viewtopic.php?t=186438 https://www.raspberrypi.com/documentation/computers/configuration.html#part5.2

 

[mdsimon2]

IMO the 8ch pins were applied correctly, sure there is a difference:

pavel@hp:~$ diff overlay_*
1320c1320
<             rsts = <0x20>;
---
>             rsts = <0x1020>;
2765c2765
<                         pins = "gpio18\0gpio19\0gpio20\0gpio21";
---
>                         pins = "gpio18\0gpio19\0gpio20\0gpio22\0gpio24\0gpio26\0gpio21\0gpio23\0gpio25\0gpio27";
3083c3083
<                         pins = "gpio18\0gpio19\0gpio20\0gpio21";
---
>                         pins = "gpio18\0gpio19\0gpio20\0gpio22\0gpio24\0gpio26\0gpio21\0gpio23\0gpio25\0gpio27";

But I do not see any master/slave card changes in those dumps, no spdif or capture_link string, etc, all i2s configs have status disabled. Debugging e.g. https://forums.raspberrypi.com/viewtopic.php?t=186438 https://www.raspberrypi.com/documentation/computers/configuration.html#part5.2

Sorry, I had just grep'd the files for "i2s" and "8ch" and didn't see any changes. I also did not have any of the master / slave overlays in place.

Just set it up with the i2s slave overlay and works great! Much easier / faster than compiling the kernel. Also attached the overlay log for reference.

Michael

 

[DWPress]

You guys are making me want a RPi5 just to get back into my audio coding days. BUT NOOOO - so much else to do - can't go down that rabbit hole.