USB stereo output issue

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

// GUItool: begin automatically generated code
AudioEffectEnvelope      envelope1;      //xy=380.25000762939453,1945.7500286102295
AudioSynthWaveformSine   sine1;          //xy=415,1821.25
AudioEffectDelay         delay1;         //xy=572.5000076293945,2039.0000305175781
AudioMixer4              mixer2;         //xy=865.0000152587891,2018.7500305175781
AudioMixer4              mixer1;         //xy=871.5000152587891,1942.2500305175781
AudioOutputUSB           usb1;           //xy=1085.0000038146973,1950
AudioSynthWaveform       waveform3; //xy=1354.4443359375,778.8888549804688
AudioSynthWaveform       waveform4; //xy=1358.4443359375,704.8888549804688
AudioMixer4              mixer3; //xy=1532.4443359375,729.8888549804688
AudioSynthWaveform       filterFreqMod1;  //xy=1585.4443359375,902.8888549804688
AudioFilterStateVariable filter2; //xy=1707.4443359375,730.8888549804688
AudioSynthWaveform       AMod1;           //xy=1762.4443359375,877.8888549804688
AudioSynthWaveformDc     dc2; //xy=1769.4443359375,924.8888549804688
AudioMixer4              mixer4; //xy=1933.4443359375,865.8888549804688
AudioEffectMultiply      multiply2; //xy=1936.4443359375,737.8888549804688
AudioOutputAnalog        dac2; //xy=2102.4443359375,734.8888549804688
AudioConnection          patchCord1(envelope1, delay1);
AudioConnection          patchCord2(envelope1, 0, mixer1, 0);
AudioConnection          patchCord3(sine1, envelope1);
AudioConnection          patchCord4(delay1, 0, mixer2, 0);
AudioConnection          patchCord5(mixer2, 0, usb1, 1);
AudioConnection          patchCord6(mixer1, 0, usb1, 0);
// GUItool: end automatically generated code






void setup() {
  // allocate enough memory for the delay
  AudioMemory(120);
  
  // enable the audio shield
//  sgtl5000_1.enable();
//  sgtl5000_1.volume(0.5);
  
  // configure a sine wave for the chirp
  // the original is turned on/off by an envelope effect
  // and output directly on the left channel
  sine1.frequency(1000);
  sine1.amplitude(0.5);

  // create 3 delay taps, which connect through a
  // mixer to the right channel output
  delay1.delay(0, 300);

  mixer1.gain(0, 0.5);
  mixer2.gain(0, 0.5);
  
}

void loop() {
  envelope1.noteOn();
  delay(36);
  envelope1.noteOff();
  delay(4000);
}