Super Simple Sampler for M5Stack-Fire board. Open in Arduino IDE.

SuperSimpleSampler.ino

/* A super simple sampler for the M5Stack-Fire board */

//#include <TFT_eSPI.h>
#include <M5Display.h>                 // This library is a lot faster! But also a lot larger.

#define speaker      25
#define microphone   34
#define numberOfBits  8
#define channel       0
#define graphWidth       320
#define graphHeight      120
#define backlight    32

TFT_eSPI    tft = TFT_eSPI();
TFT_eSprite img = TFT_eSprite(&tft);

void setup() {
  pinMode( microphone, INPUT );
  //set pwm on backlight
  ledcAttachPin( backlight, 0);
  ledcSetup( 0, 1300, 16 );
  ledcWrite( 0, 0xFFFF  / 16  ); //dimming the backlight will produce more base noise   
  dacWrite( speaker, 0);
  tft.init();
  tft.setRotation(1);
  tft.fillScreen( TFT_BLACK );
  tft.setTextSize( 2 );
  img.setColorDepth(8);
  img.createSprite( graphWidth, graphHeight );
}

uint32_t counter = 0;
int frameRate = 0;
time_t savedTime;

void loop() {
  img.fillSprite(TFT_GREEN);
  uint16_t previous = map( analogRead( microphone ), 0, 4096, 0, graphHeight );
  counter++;
  uint16_t amplitude;
  for ( uint16_t sample = 1; sample < graphWidth; sample++) {
    amplitude = map( analogRead( microphone ), 0, 4096, 0, graphHeight );
    img.drawLine( sample - 1, previous, sample, amplitude, ILI9341_RED );
    previous = amplitude;
    counter++;
  }
  frameRate++;
  if ( savedTime != time(NULL) ) {
    savedTime = time(NULL);
    tft.setCursor(20, 140);
    tft.printf( "%6iHz    %4i FPS", counter, frameRate );
    counter = 0;
    frameRate = 0;
  }
  img.pushSprite( 0, 0 );
}