Crackling sound on i2s with internal DAC since 2.0.10

[harbaum]

Board

ESP32 dev board

Device Description

DevKitC

Hardware Configuration

Speaker on GPIO25

Version

latest master (checkout manually)

IDE Name

Arduino IDE

Operating System

Linux and Windows

Flash frequency

40Mhz

PSRAM enabled

no

Upload speed

921000

Description

This demo sketch used to play a rectangle wave form on GPIO25 it works on 2.0.6 to 2.0.9

Since 2.0.10 sound is distorted and has a crackling noise overlaid. Oscilloscope shows short spikes in the rectangle signal.

Sketch

#include "driver/i2s.h"

unsigned short snd_buffer[64];

void setup() {
    static const i2s_config_t i2s_config = {
    .mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_TX | I2S_MODE_DAC_BUILT_IN),
    .sample_rate = 24000,
    .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,

    .channel_format = I2S_CHANNEL_FMT_ONLY_RIGHT,
    .intr_alloc_flags = 0,
    .dma_buf_count = 4,
    .dma_buf_len = 64,   // 64 samples
    .use_apll = true
  };
  i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
  i2s_set_dac_mode(I2S_DAC_CHANNEL_RIGHT_EN);
}

void loop() {
  // generate square wave
  for(int i=0;i<32;i++)  snd_buffer[i] = 0x0000;
  for(int i=32;i<64;i++) snd_buffer[i] = 0x1000;

  size_t bytesOut = 0;
  i2s_write(I2S_NUM_0, snd_buffer, sizeof(snd_buffer), &bytesOut, 0);
  printf("BytesOut: %d\n", bytesOut);
}

Debug Message

Endless sequence of
BytesOut: 128
BytesOut: 0

No difference in output between 2.0.9 and 2.0.10

Other Steps to Reproduce

No response

I have checked existing issues, online documentation and the Troubleshooting Guide

• I confirm I have checked existing issues, online documentation and Troubleshooting guide.

[VojtechBartoska]

@me-no-dev Please help with triage, thanks

[SuGlider]

@harbaum - DAC only supports 8 bits sample per channel. This is the problem.
Anyway, this is an IDF issue, not related to the Arduino Core directly.

[SuGlider]

You can try this:

    // adjust the samples to 8bit ch1 + 8bit ch2
    .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,        // the DAC only uses 8 bits per channel
    .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,        // stereo

or

    // adjust samples to 8bit single channel
    .bits_per_sample = I2S_BITS_PER_SAMPLE_8BIT,         // the DAC only uses 8 bits
    .channel_format = I2S_CHANNEL_FMT_ONLY_LEFT,         // mono

[harbaum]

@SuGlider Thanks for the reply. I'll give this a try asap. However,

the example on this page:
https://docs.espressif.com/projects/esp-idf/en/v4.3.5/esp32/api-reference/peripherals/i2s.html

includes this line

.bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT, /* the DAC module will only take the 8bits from MSB */

This was the reason why I chose 16 bit.

Later on the page states:

I2S_MODE_DAC_BUILT_IN = 16
Output I2S data to built-in DAC, no matter the data format is 16bit or 32 bit, the DAC module will only take the 8bits from MSB

For some reason all these comments are gone in later ESP-IDF docs.

[harbaum]

There's probably a directly relationship between arduino ESP32 board support versions (2.0.xx) and the ESP-IDF version (4.x/5.x).

This broke from 2.0.9 to 2.0.10. Where can I see what underlying ESP-IDF versions these two use?

Edit: 2.0.9 is based on ESP-IDF 4.4.4, 2.0.10 and 2.0.11 are based on 4.4.5

[harbaum]

Some more investigation. The stereo version also crackles. So does only right and only left.

On the oscilloscope i see short spikes of the intended volume/voltage but not nearly as long as expected.

[harbaum]

Interesting fact: I had left and right mixed in channel_format and set_dac_mode. That gave a sound on previous versions, while it IMHO shouldn't.

With 2.0.11 it only works with left/left or right/right. But still there's significant noise, which there isn't with 2.0.9 a and earlier. The example (now with right/right) gives a rectangle signal but with noticeable crackling noise. While the cracks are not extremely dominant in the rectangle version, they are very prominent in a real audio example.

Still, the example above produces noticeable crackling noises.

[harbaum]

You can try this:

    .bits_per_sample = I2S_BITS_PER_SAMPLE_8BIT,         // the DAC only uses 8 bits
    .channel_format = I2S_CHANNEL_FMT_ONLY_LEFT,         // mono

Switching to 8 bits doesn't make a difference.

[harbaum]

The distortions seen on the oscilloscope.

[SuGlider]

@harbaum - I've found what solves the issue.

Please use .use_apll = false instead of true.
I don't know exactly what has changed from the IDF 4.4 precompiled libraries used in the Arduino Core 2.0.9 to the Arduino Core 2.0.10.

It seems that it's nothing that has chaged in the Arduino Layer... maybe something changed in the IDF side.
I'll try to quickly see if there is something in the IDF github that may justify this finding.

[SuGlider]

I couldn't see any change in https://github.com/espressif/esp-idf/blob/release/v4.4/components/driver/i2s.c that would justify such change. Maybe something changed in the components used to calculate and set the I2S source clock when it uses APLL.

Thanks for reporting! You may want to open an issue within IDF github to report this APLL issue.