Hello,
I am very new to the Teensy topic. With four MAX4466s, two Audioshields and one Teensy 3.2, I'm trying to build a quad-recording device based on the Sparkfun tutorial. I tried to extend the stereo recording sketch from "inmidi" to 4 channels. But it does not work.

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

// GUItool: begin automatically generated code
AudioInputI2SQuad        i2s_quad1;      //xy=375,276
AudioRecordQueue         queue3;         //xy=580,292
AudioRecordQueue         queue4;         //xy=580,329
AudioRecordQueue         queue1;         //xy=581,222
AudioRecordQueue         queue2;         //xy=582,258
AudioConnection          patchCord1(i2s_quad1, 0, queue1, 0);
AudioConnection          patchCord2(i2s_quad1, 1, queue2, 0);
AudioConnection          patchCord3(i2s_quad1, 2, queue3, 0);
AudioConnection          patchCord4(i2s_quad1, 3, queue4, 0);
AudioControlSGTL5000     sgtl5000_2;     //xy=131,135
AudioControlSGTL5000     sgtl5000_1;     //xy=135,40
// GUItool: end automatically generated code


// which input on the audio shield will be used?
const int myInput = AUDIO_INPUT_LINEIN;
//const int myInput = AUDIO_INPUT_MIC;


// 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 // 254?
//#define SDCARD_MOSI_PIN  11  // not actually used
//#define SDCARD_SCK_PIN   13  // not actually used

// Remember which mode we're doing
int mode = 0;  // 0=stopped, 1=recording, 2=playing



// The file where data is recorded
File frec;

void setup() {
  // record queue uses this memory to buffer incoming audio.
  AudioMemory(120); // 60

  // Enable the audio shield, select input, and enable output
  sgtl5000_1.setAddress(LOW);
  sgtl5000_1.enable();
  sgtl5000_1.inputSelect(myInput);
  sgtl5000_1.volume(0.5);
  
  
 sgtl5000_2.setAddress(HIGH);
 sgtl5000_2.enable();
 sgtl5000_2.inputSelect(myInput);
 sgtl5000_2.volume(0.5);


  // Initialize the SD card
  SPI.setMOSI(SDCARD_MOSI_PIN);
  SPI.setSCK(SDCARD_SCK_PIN);
  if (!(SD.begin(SDCARD_CS_PIN))) {
    // stop here if no SD card, but print a message
    while (1) {
      Serial.println("Unable to access the SD card");
      delay(500);
    }
  }

  startRecording();
}


void loop() {
  if (millis() > 10000 && mode == 1) {
    stopRecording();
  }
  else {
    if (mode == 1) continueRecording();
  }
}

void startRecording() {
  Serial.println("StartRecording");
  if (SD.exists("RECORD.RAW")) {
    SD.remove("RECORD.RAW");
  }
  frec = SD.open("RECORD.RAW", FILE_WRITE);
  if (frec) {
    Serial.println("File Open");
    queue1.begin();
    queue2.begin();
    queue3.begin();
    queue4.begin();
    mode = 1;
  }

}

// write all 512 bytes to the SD card   
void continueRecording() {
  if (queue1.available() >= 2 && queue2.available() >= 2  && queue3.available() >= 2 && queue4.available() >= 2) {
    byte buffer[512];
    byte buffer1[128];
    byte buffer2[128];
    byte buffer3[128];
    byte buffer4[128];
    memcpy(buffer1, queue1.readBuffer(), 128);
    memcpy(buffer2, queue2.readBuffer(), 128);
    memcpy(buffer3, queue3.readBuffer(), 128);
    memcpy(buffer4, queue4.readBuffer(), 128);
    queue1.freeBuffer();
    queue2.freeBuffer();
    queue3.freeBuffer();
    queue4.freeBuffer();
    int b = 0;
    for (int i = 0; i < 512; i += 8) {
      buffer[i] = buffer1[b];
      buffer[i + 1] = buffer1[b + 1];
      buffer[i + 2] = buffer2[b];
      buffer[i + 3] = buffer2[b + 1];
      buffer[i + 4] = buffer3[b];
      buffer[i + 5] = buffer3[b + 1];
      buffer[i + 6] = buffer4[b];
      buffer[i + 7] = buffer4[b + 1];
      b = b+4;
    }
    elapsedMicros usec = 0;
    frec.write(buffer, 512);  //256 or 512 (dudes code)
    Serial.print("SD write, us=");
    Serial.println(usec);
  }
}

void stopRecording() {
  Serial.println("StopRecording");
  queue1.end();
  queue2.end();
  queue3.end();
  queue4.end();
  // flush buffer
  while (queue1.available() > 0 && queue2.available() > 0 && queue3.available() > 0 && queue4.available() > 0) {
    queue1.readBuffer();
    queue1.freeBuffer();
    queue2.readBuffer();
    queue2.freeBuffer();
    queue3.readBuffer();
    queue3.freeBuffer();
    queue4.readBuffer();
    queue4.freeBuffer();
  }
  frec.close(); // close file
  mode = 4;
}
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This is a recording of a 1 kHz Sine-wave.

i hope someone can help me.

p.s.: Sorry, I have not spoken much English since school and have some problems expressing myself.