teensy-audio/examples/HardwareTesting/WavFilePlayerUSB/WavFilePlayerUSB.ino

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

AudioPlaySdWav           playWav1;
AudioOutputUSB           audioOutput; // must set Tools > USB Type to Audio
AudioOutputAnalog        dac;
AudioConnection          patchCord1(playWav1, 0, audioOutput, 0);
AudioConnection          patchCord2(playWav1, 1, audioOutput, 1);
AudioConnection          patchCord3(playWav1, 0, dac, 0);

// Use these with the Teensy Audio Shield
#define SDCARD_CS_PIN    10
#define SDCARD_MOSI_PIN  7
#define SDCARD_SCK_PIN   14

// Use these with the Teensy 3.5 & 3.6 SD card
//#define SDCARD_CS_PIN    BUILTIN_SDCARD
//#define SDCARD_MOSI_PIN  11  // not actually used
//#define SDCARD_SCK_PIN   13  // not actually used

// Use these for the SD+Wiz820 or other adaptors
//#define SDCARD_CS_PIN    4
//#define SDCARD_MOSI_PIN  11
//#define SDCARD_SCK_PIN   13

void setup() {
  Serial.begin(9600);

  // Audio connections require memory to work.  For more
  // detailed information, see the MemoryAndCpuUsage example
  AudioMemory(20);

  SPI.setMOSI(SDCARD_MOSI_PIN);
  SPI.setSCK(SDCARD_SCK_PIN);
  if (!(SD.begin(SDCARD_CS_PIN))) {
    // stop here, but print a message repetitively
    while (1) {
      Serial.println("Unable to access the SD card");
      delay(500);
    }
  }
}

void playFile(const char *filename)
{
  playWav1.play(filename);
  // A brief delay for the library read WAV info
  delay(5);
  // Simply wait for the file to finish playing.
  while (playWav1.isPlaying()) {
  }
}

void loop() {
  playFile("SDTEST1.WAV");  // filenames are always uppercase 8.3 format
  delay(500);
  playFile("SDTEST2.WAV");
  delay(500);
  playFile("SDTEST3.WAV");
  delay(500);
  playFile("SDTEST4.WAV");
  delay(1500);
}

// A known problem occurs on Macintosh computers, where the Mac's driver
// does not seem to be able to adapt and transmit horribly distorted
// audio to Teensy after a matter of minutes.  An imperfect workaround
// can be enabled by editing usb_audio.cpp.  Find and uncomment
// "#define MACOSX_ADAPTIVE_LIMIT".  More detailed info is available here:
// https://forum.pjrc.com/threads/34855-Distorted-audio-when-using-USB-input-on-Teensy-3-1?p=110392&viewfull=1#post110392