teensy-audio/examples/Analysis/MonoPeakMeterAnalog/MonoPeakMeterAnalog.ino

/* Mono peak meter example using Analog objects. Assumes Teensy 3.1

At a minimum DC decouple audio signals to/from Teensy pins with capacitors in the signal paths both in and out, 10uF is often used.
Possibly worthwhile to set up virtual ground at 3v3/2 for both, or if changing DAC REF to 1.2V then 1.2V/2 for output side.

This example code is in the public domain
*/

#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>

AudioInputAnalog        audioInput(A0);         // A0 is pin 14, feel free to change.
AudioAnalyzePeak        peak;
AudioOutputAnalog       audioOutput;            // DAC pin.

AudioConnection c1(audioInput,peak);
AudioConnection c2(audioInput,audioOutput);

void setup() {
  AudioMemory(4);
  Serial.begin(9600);
}

// for best effect make your terminal/monitor a minimum of 31 chars wide and as high as you can.

elapsedMillis fps;

void loop() {
  if (fps > 24) {
    if (peak.available()) {
      fps = 0;
      uint8_t monoPeak = peak.read() * 30.0;
      Serial.print("|");
      for (uint8_t cnt=0;cnt<monoPeak;cnt++) {
        Serial.print(">");
      }
      Serial.println();
    }
  }
}