How to change volume for internal DAC on esp32 ?

[PowerTcX]

Hi, i have a noob question, how to change volume in this example ?

/**
 * @file streams-url_mp3-analog.ino
 * @author Phil Schatzmann
 * @brief decode MP3 stream from url and output it on I2S
 * @version 0.1
 * @date 2021-96-25
 * 
 * @copyright Copyright (c) 2021
 */

// install https://github.com/pschatzmann/arduino-libhelix.git

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


URLStream url("ssid","password");
AnalogAudioStream analog; // final output of decoded stream
EncodedAudioStream dec(&analog, new MP3DecoderHelix()); // Decoding stream
StreamCopy copier(dec, url); // copy url to decoder


void setup(){
  Serial.begin(115200);
  AudioLogger::instance().begin(Serial, AudioLogger::Info);  

  // setup analog
  auto config = analog.defaultConfig(TX_MODE);
  analog.begin(config);

  // setup I2S based on sampling rate provided by decoder
  dec.setNotifyAudioChange(analog);
  dec.begin();

// mp3 radio
  url.begin("http://stream.srg-ssr.ch/m/rsj/mp3_128","audio/mp3");

}

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

[pschatzmann]

It's in the documentation: https://github.com/pschatzmann/arduino-audio-tools/wiki/Volume-Control