Does this library only work for 16-bit audio? How about mono instead of stereo?

[frohro]

Hi @pschatzmann ,

This problem could be something to do with my OS. I am using Ubuntu 24.04 with pulseaudio selected it Audacity.

My testing seems to indicate that this library works for 16-bit audio in stereo, but not for 24-bit or 32-bit audio, even at lower sample rates. Nothing in mono works for me. I have been changing the Audacity settings to the same format I'm testing. Here is the basic program I started withe As is, it works:

#include "Adafruit_TinyUSB.h"
#include "AudioTools.h"

AudioInfo info(48000, 2, 16);
SineWaveGenerator<int16_t> sineWave(32000);                // subclass of SoundGenerator with max amplitude of 32000
GeneratedSoundStream<int16_t> sound(sineWave);             // Stream generated from sine wave
Adafruit_USBD_Audio usb;

size_t readCB(uint8_t* data, size_t len, Adafruit_USBD_Audio& ref) {
  return sound.readBytes(data, len);
}

void setup() {
  Serial.begin(115200);

  // Setup sine wave
  sineWave.begin(info, 2000.0);

  // Start USB device as Audio Source
  usb.setReadCallback(readCB);
  usb.begin(info.sample_rate, info.channels, info.bits_per_sample);

  // If already enumerated, additional class driverr begin() e.g msc, hid, midi won't take effect until re-enumeration
  if (TinyUSBDevice.mounted()) {
    TinyUSBDevice.detach();
    delay(10);
    TinyUSBDevice.attach();
  }
}

void loop() {
  // use LED do display status
  usb.updateLED();
}

I was getting ready to test 24 bits, so to make sure it wasn't the amount of data causing the problem, I decided to test mono instead of stereo. To do that, I changed this line only:

AudioInfo info(48000, 1, 16); // sample rate, channels, bits per sample

and got this:

I also tried 24 bits by changing these lines:

AudioInfo info(8000, 2, 24); // sample rate, channels, bits per sample
SineWaveGenerator<int24_t> sineWave(32000);                // subclass of SoundGenerator with max amplitude of 32000
GeneratedSoundStream<int24_t> sound(sineWave);   

Changing the sample rate seems to work okay with 16-bit stereo, but not with 24 bits (or 32 bits). Mono does not work for me with any bit rate. I suspect only 16-bit stereo audio works. Is that correct? What might I be doing wrong?

Thanks,
Rob

[frohro]

I am still testing this @pschatzmann . Now I am using your sawtooth example. I have been able to get mono to work now. I'm not sure why I was having difficulty there. I am still not getting 24 bits to work.

#include "Adafruit_TinyUSB.h"
#include "AudioTools.h"  // https://github.com/pschatzmann/arduino-audio-tools

Adafruit_USBD_Audio usb;
AudioInfo info(48000, 1, 16);
SawToothGenerator<int16_t> sawtooth;               
GeneratedSoundStream<int16_t> sawthooth_stream(sawtooth);

void setup() {
  Serial.begin(115200);
  //while(!Serial);  // wait for serial

  // generate 10 hz 
  sawtooth.begin(info, 10.0f);

  // Start USB device as Audio Source
  usb.setInput(sawthooth_stream);
  usb.begin(info.sample_rate, info.channels, info.bits_per_sample);
}

void loop() {
  // optional: use LED do display status
  usb.updateLED();
}

[pschatzmann]

24 bit might be tricky and you need to figure out what this means! There are basically 2 interpretations: one is that it is represented by 3 bytes and another that it is represented by 4 bytes. On the ESP32 and I think on the RP2040 I am using int24_4bytes_t. Maybe usb expects int24_3bytes_t ?

ChatGPT gives: 4 bytes (32 bits) per sample: Common in USB Audio Class 2.0+ for efficiency.
3 bytes (24 bits) per sample: Possible, but less frequently used in USB audio transmission.

[pschatzmann]

In the Adafruit_audio_config.h bytes per sample are defined as 2!

[frohro]

Thanks, @pschatzmann ! So if bytes per sample are defined as 2, it looks like doing other than 16-bit audio will likely not be easy. :-) For now, 16 bits will have to do I guess. Thanks for finding that up for me in the source. Does AudioTools have a filter that will do better than just truncating the last byte of the 24 bits and if so is that already in the FormatConverter?
Thanks,
Rob

[pschatzmann]

I committed some change so that you can try to redefine BITS_PER_SAMPLE in the build_flags of platformio.ini.

My number format conversion is currently relying on floating point multiplications: This might not be the fastest approach, but it was easy to implement and good enough in terms of speed.

[frohro]

I did a quick check with this platformio.ini

[env:pico]
platform = https://github.com/maxgerhardt/platform-raspberrypi.git
; board_build.f_cpu = 133000000L
board = pico
framework = arduino
board_build.core = earlephilhower
build_flags = 
    -DUSE_TINYUSB
    -DCFG_TUSB_RHPORT0_MODE=OPT_MODE_DEVICE
    -DCFG_TUD_AUDIO=1
    -DCFG_TUD_CDC=1
    -DRP2040_HOWER
    -DBITS_PER_SAMPLE=24
lib_deps = 
    https://github.com/pschatzmann/Adafruit_TinyUSB_Arduino.git#Audio
    https://github.com/pschatzmann/arduino-audio-tools.git
upload_protocol = picotool
monitor_speed = 115200

and this .cpp

#include "Adafruit_TinyUSB.h"
#include "AudioTools.h"  // https://github.com/pschatzmann/arduino-audio-tools

Adafruit_USBD_Audio usb;
AudioInfo info(48000, 2, 24);
SawToothGenerator<int24_t> sawtooth;               
GeneratedSoundStream<int24_t> sawthooth_stream(sawtooth);

void setup() {
  Serial.begin(115200);
  //while(!Serial);  // wait for serial

  // generate 10 hz 
  sawtooth.begin(info, 10.0f);

  // Start USB device as Audio Source
  usb.setInput(sawthooth_stream);
  usb.begin(info.sample_rate, info.channels, info.bits_per_sample);
}

void loop() {
  // optional: use LED do display status
  usb.updateLED();
}

and got this, so I'm still not successful.