short noise at new music start

[vorosj]

I wrote a simple mp3 player using the library. (esp32, oled display, SD, Bluetooth or wired earplug)
It's working, however there is a problem. When it starts a new .mp3, there is a short noise in the beginning, probably something left in a buffer. What I am missing?
the code pieces:

I2SStream i2s;
VolumeStream volumeI2s(i2s);
A2DPStream bt;
VolumeStream volumeBt(bt);
EncodedAudioStream decoder(&volumeBt, new MP3DecoderHelix()); // Decoding stream
StreamCopy copier;

//setup
decoder.begin();
decoder.setOutput(&volumeI2s);
auto cfg = i2s.defaultConfig(TX_MODE);
i2s.begin(cfg);
auto config_vol = volumeI2s.defaultConfig();
volumeI2s.begin(config_vol); // we need to provide the bits_per_sample and channels
volumeI2s.setVolume(0.3);
...
copier.begin(decoder, audioFile); // start
...
if ((copier.copy() == 0))
{ copier.end();
...
audioFile = SD.open(s);
copier.begin(decoder, audioFile);
...
}

[pschatzmann]

Did you try to close and reopen the decoder ?
After all the decoding of an mp3 segment depends on the previous segment, which does not make any sense when you change the file.

[vorosj]

Thank you for the fast reply.
Not sure, how to close-reopen it.

[vorosj]

I tried this, the noise is still there:
copier.end();
decoder.end();
delay(100);
decoder.begin();
copier.begin(decoder, audioFile);

[vorosj]

I did a detailed test. First I flushed all the buffers. Still noise. Then I checked all the steps one by one, and found, that the decoderBt.end() makes the noise. Even if I set the volume to zero.
If I try to simply remove the decoderBt.end() from the sequence, then the copier.begin(decoderBt, audioFile) makes the exact same noise.
I tried to send the noise to thin air with decoderBt.setOutput(nullptr), but there is no such output.
Not easy... :-)

volumeBt.setVolume(0);
delay(3000);
// Flush/reset components
Serial.println("decoderFlush");
decoderBt.flush(); // Clear decoder buffer
delay(3000);
Serial.println("volumei2sFlush");
volumeI2s.flush(); // Flush volume stream
delay(3000);
Serial.println("i2sFlush");
i2s.flush(); // Clear I2S buffer
// decoderBt.setOutput(nullptr); // Disconnect decoder temporarily
delay(3000);
Serial.println("decoderEnd");
decoderBt.end(); // Reset decoder state
delay(3000);
Serial.println("decoderBegin");
decoderBt.begin();
delay(3000);
Serial.println("decodersetOutput");
decoderBt.setOutput(&volumeI2s); // Reconnect decoder output
delay(3000);
Serial.println("audioFileSdOpen");
audioFile = SD.open(s);
delay(3000);
Serial.println("decoderBegin");
decoderBt.begin();
delay(3000);
Serial.println("copierBegin");
copier.begin(decoderBt, audioFile);
volumeBt.setVolume(hangero);

[pschatzmann]

I don't quite understand your logic above: you don't write anything to I2S ?
You could use a NullStream to ignore the output.

It could potentially also be your delays and Serial.prints: If you use an old version of the library you will get noise when you stop sending any audio to I2S.

Do you get the same issue if you use the AudioPlayer class instead ?
What DAC are you using ?

[pschatzmann]

I could not reproduce your issue (with an AudioKit) with the following simplified test sketch which uses your original logic.
AudioBoardStream is just a glorified I2SStream which also sets up the codec via I2C.
I used the ESP Arduino core version 3.1.2 for the test.

#include <SPI.h>
#include <SD.h>
#include "AudioTools.h"
#include "AudioTools/AudioLibs/AudioBoardStream.h"
#include "AudioTools/AudioCodecs/CodecMP3Helix.h"


const int chipSelect=PIN_AUDIO_KIT_SD_CARD_CS;
AudioBoardStream i2s(AudioKitEs8388V1); // final output of decoded stream
EncodedAudioStream decoder(&i2s, new MP3DecoderHelix()); // Decoding stream
File audioFile;
StreamCopy copier(decoder, audioFile);

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

  // setup I2S
  auto config = i2s.defaultConfig(TX_MODE);
  config.sd_active = true;
  i2s.begin(config);

  // setup decoder
  decoder.begin();

  // setup SD
  SD.begin(chipSelect);

  // play all files
  audioFile = SD.open("/ZZ Top/Unknown Album/Lowrider.mp3");
  copier.copyAll();

  audioFile = SD.open("/ZZ Top/Unknown Album/Zztop - Cocaine.mp3");
  copier.copyAll();
}

void loop(){
  delay(1000);
}

Are you sure that your issue is not with your mp3 file ?

[vorosj]

Thank you very much for so much effort to solve my problem.
I try your sample code as soon as getting home. I have the Audiokit too, first I try it, then modify the code for my hw with the PCM5102.

"If you use an old version of the library you will get noise when you stop sending any audio to I2S."
I linked them to .ini this way, is it correct? (tried without the .git, same noise)
lib_deps =
https://github.com/pschatzmann/arduino-audio-tools.git
https://github.com/pschatzmann/arduino-libhelix.git

"You could use a NullStream"
Not sure how to do that. decoderBt.setOutput(NullStream) compiler error.

"What DAC are you using ?"
A PCM5102 board, working, the sound is good.

"Are you sure that your issue is not with your mp3 file ?"
Yes, because perfect on other device, and playing first after reset is good on my program as well, the noise is coming before the next .mp3's start.

[pschatzmann]

Maybe you also try with Arduino: PlatformIO can be tricky with the versions of the ESP32 core.
NullStream is a class: you need to define an object first.

If your PCM5102 has a XMT pin, you can use it to mute it when you don't send any data.

[vorosj]

"If your PCM5102 has a XMT pin, you can use it to mute it when you don't send any data."
Last chance... :-)
First I tried your simple test in my code.
I inserted this segment to the end of my setup, and commented ot the loop, and put there a delay only.
If your PCM5102 has a XMT pin, you can use it to mute it when you don't send any data.
//-----------------------------------------------
Serial.println(" Test start");

// play all files
audioFile = SD.open("/sine1/1kHz.mp3");
copier.copyAll();

audioFile = SD.open("/sine1/Klug.mp3");
copier.copyAll();
//-----------------------------------------------
In order to make the test as clean and informative as possible, the first file is a 5sec 1kHz sine wave. The second is a Hillary Klug song. The noise before the song is there, and I think it's about a 0.2sec part of the sine wave. Later I check it with scope to be sure.

It seems to be a dead end. Really strange.

Now I will try your sample on the Audio kit, without modding a single letter... :-)
Well, except the song titles.
And a sample code with the player class too.

[pschatzmann]

If you use your custom mp3 files, you need to make sure that you fade out and add enough silence at the end.
Alternatively you can try to write enough silence to I2S after you stop sending data ....

The esp32 config has an auto_clear flag, but this should be active by default.

[vorosj]

I didn't know it, thank you. Maybe a properly coded .mp3 has a silent tail? It seems to be important, when I stop the song before it ends, and load another one. I first observed the noise after manually stop a song and start another one. Then tested it this way, and with my own short .mp3's to avoid waiting for the end of long songs. So it's possible, that I misunderstood the situation.

you can try to write enough silence to I2S after you stop sending data ....
A tried flushing the i2s buffer, isn't it clearing any remaining samples?

I suspect it's more like the decoder's feature. If I ended the processes one by one, the noise appeared at decoder.end(). This makes possible to mute by hw. Unfortunately there is a Bluetooth mode as well.

So I like to find a better way to the stop - start another song problem. And have to check, if there is the noise between proper .mp3 songs.
Maybe there is a sample code for the [stop and start new] case?

[vorosj]

A simple test proved that the noise is not in an i2s buffer: in the above code, I set the volume to zero for the 1kHz.mp3 and 1 for the song, and the short noise is there - so it's the decoder.

[pschatzmann]

If you set the volume to 0, the decoder only outputs silence and you had the issue even before calling decoder.end()!

Did you try the writeSilence(): The default I2S buffer size is 6 * 512 so I would try with

 for (int i=0;j < I2S_BUFFER_COUNT, j++) i2s.writeSilence(I2S_BUFFER_SIZE);

and if this does not help, try to make it much bigger.

As mentioned above, this is only necessary if your mp3 file does not contain enough silence in the end.
I did my tests with and without

• calling decoder.end()
• caling delay()

without having any issue. The other thing that I have suggested, is to check with Arduino.

You can also call i2s.end() to prevent any output, but on some DACs this might also create some pops, so using the XMT pin to silence your DAC would be the better approach.