I2S microphone with Arduino

Hardware MKR Family MKR1000
1

Im working with the sph0645 I2S microphone and an Arduino MKR 1010. I can read the data from the microphone but the 5 first bits from the sph0645 are always high.
This is the code I'm using:

/*
 This example reads audio data from an Invensense's ICS43432 I2S microphone
 breakout board, and prints out the samples to the Serial console. The
 Serial Plotter built into the Arduino IDE can be used to plot the audio
 data (Tools -> Serial Plotter)

 Circuit:
 * Arduino/Genuino Zero, MKR family and Nano 33 IoT
 * ICS43432:
   * GND connected GND
   * 3.3V connected to 3.3V (Zero, Nano) or VCC (MKR)
   * WS connected to pin 0 (Zero) or 3 (MKR) or A2 (Nano)
   * CLK connected to pin 1 (Zero) or 2 (MKR) or A3 (Nano)
   * SD connected to pin 9 (Zero) or A6 (MKR) or 4 (Nano)

 created 17 November 2016
 by Sandeep Mistry
 */

#include <I2S.h>

void setup() {
  // Open serial communications and wait for port to open:
  // A baud rate of 115200 is used instead of 9600 for a faster data rate
  // on non-native USB ports
  Serial.begin(115200);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  // start I2S at 8 kHz with 32-bits per sample
  if (!I2S.begin(I2S_PHILIPS_MODE, 48000, 32)) {
    Serial.println("Failed to initialize I2S!");
    while (1); // do nothing
  }
}

void loop() {
  // read a sample
  int sample = I2S.read();
  Serial.print("Sample 32 bits: ");
  Serial.println(String(sample, BIN));
  int32_t signed_sample_18bits = (sample>>14) & 0x0003FFFF; //convert 32bits into 18bits signed
  //int32_t signed_sample_18bits = 0b011111111111111111; // Debug conversion: 0b100000000000000000 0b111111111111111111 0b011111111111111111 
  Serial.print("Sample 18 bits: ");
  Serial.println(String(signed_sample_18bits, BIN));
  int32_t sign_bit = signed_sample_18bits >> 17; // only keep the sign bit
  int32_t absolute_sample = signed_sample_18bits & 0x0001FFFF; //taking off the sign bit

  delay(100);

  if (sign_bit == 1) {
    absolute_sample = ~absolute_sample & 0x0001FFFF; // Invert + 1 to make 2's compliment
    absolute_sample += 1;
    //Serial.print("-");
    absolute_sample *= -1;
  }

  Serial.println(absolute_sample);
  delay(200);

}

The Data Format is I2S, 24 bit, 2’s compliment, MSB first. The Data Precision is 18 bits, unused bits are zeros. So I made a conversion of the data but I still get only negative samples. Do you have a solution?

2

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