How to remove INMP441 MEMS microphone low-frequency noise

Question

I have code that allows me to record I2S audio from the INMP441 MEMS microphone module using an ESP32. The data is read from the data out pin of the device.

When I take the Fourier transform of this signal while recording a 2 kHz tone, I get a large low-frequency noise component that seems to saturate the ADC, see below. The first has 2048 samples while the second has 8192:

I am not sure what the source of this noise is and how one can remove it.

Things that may be important:

• I am transmitting WiFi signals at the same time I am recording.

Setup:

Answer 1

The issue was due to the fact that my software implementation was incorrect. The microphone I am using samples using 24 bits and I did not account for this.

Previously I would read and cast sets of 2 consecutive bytes assuming each sample was two bytes where in reality each sample was three. This meant I was casting incorrectly

Reading bytes from the samples buffer and converting them to uint_16 should have been done as follows:

i2s_read((i2s_port_t)uI2SInterfaceIndex, &buffer16, 4*256, &bytesRead, 100);

int samplesRead = bytesRead / 4;
for (int i = 0; i < samplesRead; i++) {
    m_pTimeChunk->m_vvfTimeChunks[uI2SInterfaceIndex][i] = ((buffer16[4*i+2] << 8) | (buffer16[4*i+3])); 
}

Where every third byte is discarded and only two are used.