Audio Volume Fluctuations with ESP32 and MAX98357A

[mikhailbot]

I'm having some weirdness I'm hoping there's an easy explanation for. The snippet is below, but using the basic viola.h WAV to I2S example the volume isn't consistent during the short audio track. There's some minor crackling here and there which is fine, but the volume of the track fluctuates up and down through out. I've confirmed the WAV directly from the linked URL and it doesn't have those fluctuations.

A generic ESP32-WROOM-32 board with a generic MAX98357A DAC/AMP to a small 1" 8ohm speaker (but also happens with a 3" 4ohm one). Powered from a 5V/3A good power supply just in case as well.

#include <Arduino.h>

#include "AudioFileSourcePROGMEM.h"
#include "AudioGeneratorWAV.h"
#include "AudioOutputI2S.h"

// viola sample taken from https://ccrma.stanford.edu/~jos/pasp/Sound_Examples.html
#include "viola.h"

AudioGeneratorWAV *wav;
AudioFileSourcePROGMEM *file;
AudioOutputI2S *out;

void setup()
{
    Serial.begin(115200);
    delay(1000);
    Serial.printf("WAV start\n");

    audioLogger = &Serial;
    file = new AudioFileSourcePROGMEM(viola, sizeof(viola));
    out = new AudioOutputI2S();
    out->SetGain(0.3);

    wav = new AudioGeneratorWAV();
    wav->begin(file, out);
}

void loop()
{
    if (wav->isRunning())
    {
        if (!wav->loop())
            wav->stop();
    }
    else
    {
        Serial.printf("WAV done\n");
        delay(1000);
    }
}