Laggy output when mixing multiple mp3

[Tolomaj]

Hi, I am trying to mix multiple mp3 files together and play them.

Unfortunately, after some struggle the audio that came from speaker is laggy.

My question is if is there anybody with same experience and know if I do something wrong or if this is a limitation of ESP32 witch iam using?

When I play just one track (removing anything ending in 2 and 3), the lag is not there.

My thesis is that these 3 tracks are switched on and off in loop but I don't know anymore what do differently.

This is my code running on ESP322 with external TAS5825M DAC.

#include <string.h>
#include <sys/unistd.h>
#include <sys/stat.h>
#include "esp_vfs_fat.h"
#include "sdmmc_cmd.h"
#include "driver/sdmmc_host.h"

#include "esp_system.h"
#include "dirent.h"

#include "board.hpp"

#include "AudioTools.h"
#include "AudioTools/AudioLibs/AudioSourceSD.h"
#include "AudioTools/AudioCodecs/CodecMP3Helix.h"

#include <SPI.h>
#include <SD.h>
#include "SD_MMC.h"

#include <Wire.h>
#include <TAS5825M.h>
TwoWire dac_wirea( 1 );
TAS5825M tas_daca( dac_wirea );

I2SStream i2s; // final output of decoded stream
OutputMixer<int16_t> mixer(i2s, 3);

//audio [1]
VolumeStream volume1(mixer);
EncodedAudioStream decoder1(&volume1, new MP3DecoderHelix()); // Decoding stream
StreamCopy copier1; 
File audioFile1;

//audio [2]
VolumeStream volume2(mixer);
EncodedAudioStream decoder2(&volume2, new MP3DecoderHelix()); // Decoding stream
StreamCopy copier2; 
File audioFile2;

//audio [3]
VolumeStream volume3(mixer);
EncodedAudioStream decoder3(&volume3, new MP3DecoderHelix()); // Decoding stream
StreamCopy copier3; 
File audioFile3;

void mini_main(void){
   //inicializace DAC & TAS5825M
        if ( dac_wirea.begin( DAC_I2C_SDA, DAC_I2C_SCL ) == false ) {
            printf( "error: failed to begin DAC Wire (I2C)" );
            //todo vyhlásit error
        }
	    tas_daca.begin();


  //init SD card
  SD_MMC.setPins( SD_SCK, SD_MOSI, SD_D0, SD_D1, SD_D2, SD_D3 );
  while ( !SD_MMC.begin() ) {
    Serial.println( "Error talking to SD card!" );
    delay( 100 );
  }


  // load files
  audioFile1 = SD_MMC.open("/aa.mp3");
  audioFile2 = SD_MMC.open("/bb.mp3");
  audioFile3 = SD_MMC.open("/cc.mp3");


  // setup i2s
  auto config = i2s.defaultConfig(TX_MODE);
    config.pin_bck = I2S1_SCK;
    config.pin_ws = I2S1_LRCLK;
    config.pin_data = I2S1_SDIN;
  i2s.begin(config);

  
  // set initial volume
  volume1.setVolume(0.1);
  volume1.begin();

  volume2.setVolume(0.2);
  volume2.begin();

  volume3.setVolume(0.2);
  volume3.begin();
  

  // setup decoders
  decoder1.begin();
  decoder2.begin();
  decoder3.begin();

  
  //start mixer
  mixer.begin(4608);


  // begin copy
  copier1.begin(decoder1,audioFile1);
  copier2.begin(decoder2,audioFile2);
  copier3.begin(decoder3,audioFile3);


  while(1){
    //copier loop
    copier2.copy();
    copier1.copy();
    copier3.copy();
  }
}

I hope for any help or suggestion on what to try.

[pschatzmann]

I am surprised that you don't run out of RAM since the mp3 decoder needs quite a bit of it.
I bet you are stressing out the SD drive with your logic: try to measure the impact on what you are doing!

Another theory would be that the sequential decoding would be adding to the lag. You can try to replace the mp3 with wav: if it is improving then the issue is rather the decoding, if it is getting worse, the issue is the data access....

[Tolomaj]

I am surprised that you don't run out of

RAM since the mp3 decoder needs quite a bit of it.
I use ESP32-s3 with 16MB so it has plenty of memory.

You can try to replace the mp3 with wav

It worked like charm. So the SD card is not a problem.

I probably don´t need mp3 support and can use wav. But I am curious.
Is there way to improve MP3 decoding?
Something like decoding few frames ahead?

[pschatzmann]

Maybe by using some mp3 with a smaller sample rate.

You could also try to decode to separate queues in parallel using tasks and use a spearate task just to do the mixing. Thre is a Wiki for Multicore Processing