USB(PCM2706) to ESP32 for a PC digital sound system

[alw1746]

This project uses a PCM2706 board that has a USB-to-SPDIF interface but also outputs I2S with a jumper setting. This is perfect for building a digital sound system for a PC. The I2S interface outputs 12MHz on the MCLK pin but it worked with just BCLK,LRCLK,DATA connected to the ESP32. For testing, I wired up the following components:

USB(PCM2706) -> ESP32 -> DAC(PCM5102) -> stereo amplifier

On Windows, the module shows up as Speakers (2 - USB Audio DAC) and music apps like VLC output to it just like a normal soundcard. The only catch is the Windows volume/mute control has no effect, you need to use your amplifier for that. However application-level volume control such as in VLC works as expected. Given the module is a standard USB audio device, it should be supported in Linux as well.

Sketch

/* 
Test a PCM2706 board that has a USB-to-SPDIF interface but also outputs I2S with a jumper setting.
The component connections are:    USB(PCM2706) -> ESP32 -> DAC(PCM5102) -> stereo amplifier
*/
#include "AudioTools.h"

AudioInfo info(48000, 2, 32);
I2SStream in;          //PCM2706 USB-I2S
I2SStream out;         //PCM5102 DAC
StreamCopy copier(out, in);

void setup(void) {
  Serial.begin(115200);
  // change to Warning to improve the quality
  AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Warning); 
 
  // start I2S in
  auto config_in = in.defaultConfig(RX_MODE);
  config_in.copyFrom(info); 
  config_in.i2s_format = I2S_STD_FORMAT;
  config_in.is_master = false;    //ESP32=slave,PCM2706=master
  config_in.port_no = 0;
  config_in.pin_bck = 5;
  config_in.pin_ws = 4;
  config_in.pin_data = 6;
  in.begin(config_in);

  // start I2S out
  auto config_out = out.defaultConfig(TX_MODE);
  config_out.copyFrom(info); 
  config_out.i2s_format = I2S_STD_FORMAT;
  config_out.is_master = true;
  config_out.port_no = 1;
  config_out.pin_bck = 7;
  config_out.pin_ws = 9;
  config_out.pin_data = 8;
  out.begin(config_out);
}

void loop() {
  copier.copy();
}

The PCM2706 board and ESP32-S3 Supermini(Tenstar Robot) are generic Aliexpress items while the PCM5102 is from Adafruit.

[A-KL]

Hi @alw1746,

Thanks for sharing! I'm actually building something very similar, but couldn't get it to work properly.

The sound read from PCM2706 (via I2S) is very noisy and seems to be mixed into a single channel, despite settings in windows\mac os.

I'm using the same esp32s3 board, MAX98357 I2S as output (works perfectly fine with other scatches), and almost the same USB card (without S/PDIF):

Here is my code:

#include "AudioTools.h"

AudioInfo info(44100, 2, 16);
I2SStream in;
I2SStream out;
StreamCopy copier(out, in);

void setup(void) {  
  Serial.begin(115200);
  AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Info); 

  Serial.println("starting I2S...");
  auto config_in = in.defaultConfig(RX_MODE);
  config_in.copyFrom(info); 
  config_in.i2s_format = I2S_STD_FORMAT;
  config_in.is_master = false;
  config_in.port_no = 0;
  config_in.pin_bck = I2S_IN_BCK;
  config_in.pin_ws = I2S_IN_WS;
  config_in.pin_data = I2S_IN_SD;
  in.begin(config_in);

  auto config_out = out.defaultConfig(TX_MODE);
  config_out.copyFrom(info); 
  config_out.i2s_format = I2S_STD_FORMAT;
  config_out.is_master = true;
  config_out.port_no = 1;
  config_out.pin_bck = I2S_BCK;
  config_out.pin_ws = I2S_WS;
  config_out.pin_data = I2S_SD;
  out.begin(config_out);
}

void loop() {
  copier.copy();
}

The only difference is AudioInfo info(44100, 2, 16);.
Did this format work for you? My usb module supports 48000,Hz, but only at 16-bit, not 32. Which setting did you use in Windows\Linux?

Would appreciate any help :)

[pschatzmann]

The only issue I see is the inpropoer Log level as documented in many places e.g. here !

Also double check that the PCM2706 supports 16 bits properly, if not change it to e.g. 32bits!
And finally double check if your input device requires a master clock pin...

[A-KL]

Just tested with 32bits and it works! Maybe I didn't understand the datasheet correctly:

It never mentions 32bit i2s output. @pschatzmann , thanks for the hints!

[alw1746]

I had similar problems with 44.1kHz as well. After trying various permutations of the 3 parameters (sample rate, bits, channels) I got it to work only at 48kHz 32-bit despite what the datasheet said. Perhaps it's related to some USB audio driver issue. I tried changing the Windows Device Manager Sound properties to 44100 to match the ESP32 but it did not help. Another problem you may encounter is distorted output with buzzing interference. Restarting ESP32 will not fix it, it is a driver issue. Solution:

Device Manager -> Sound -> USB AUDIO DAC Properties -> Advanced
-Select 16 bit, 44100Hz and click Test. Sound is slightly distorted.
-Select 16 bit, 48000Hz and click Test. Sound returns to normal.

The PCM2706C is 10 years old so it is possible changes to the USB driver since then has introduced some incompatibilities.