Converting 32 bit stream to 16 bit

[wegscheider]

Hi Phil:

First of all, thank you very much for the fantastic library. In a project where I want to save the output from an I2S microphone to SD card, I am running into the following problem: When I artificially generate the output (via SineWaveGenerator) in 16 bit everything works perfect. However, the microphone produces a 32 bit stream which I obviously need to convert to 16 bit. That's where I am struggling. I used the following code to test but receive only zeros on the serial monitor:

#include "AudioTools.h"

uint16_t sample_rate=44100;

SineWaveGenerator<int32_t> sine_wave(32000); // subclass of SoundGenerator with max amplitude of 32000
GeneratedSoundStream<int32_t> in_stream(sine_wave); // Stream generated from sine wave
CsvStream<int16_t> out(Serial, 1); // Output to Serial
NumberFormatConverterStreamT<int32_t, int16_t> conv(in_stream);
StreamCopy copier(out, conv);

void setup(){
Serial.begin(115200);
AudioLogger::instance().begin(Serial, AudioLogger::Warning);

sine_wave.begin(1, sample_rate, N_B4);
conv.begin();
in_stream.begin();

out.begin();
}

void loop(){
copier.copy();
}

What am I doing wrong with the converter function?

Any help is very much appreciated.

Werner

[pschatzmann]

Did you try to output the 32 bit GeneratedSoundStream directly. I propose that you leave the amplitude away in the constructor of the sine_wave or increase it to the max value of a 32 bit number.
First I just want to make sure that your sound generation is working...

[wegscheider]

Yes, the GeneratedSoundStream works just fine.

[pschatzmann]

I was running your sketch with my proposed change with
SineWaveGenerator<int32_t> sine_wave;
And for me it works like a charm:

When you use 32000 as max amplitude the converted signal is oscillating around +-0.00001490116 which gives 0 when converted to an integer!

[wegscheider]

Thank you very much! I can reproduce your result. That explains also why I got only so small numbers when using the I2S microphone.

Now for the I2S microphone which gives me 24 bit values on a 32 bit stream, what do I need to use the full 16 bit range and not only have values from 0 to 255 in my 16 bit stream? I tried to use <int24_t> streams in my sine_wave example (amplitude 8000000) but the values are still only covering 8 bits.

[pschatzmann]

Quite recently I added some functionality to determine the max number by data type. Initially I relied on the size, but this does not work for int24_t because this has 4 bytes like the int32_t.
I just committed the related change to the NumberFormatConverterStreamT which should work now with int24_t in a better way.

If the volume is still too low you can add a VolumeStream to your chain....

[wegscheider]

Thank you very much, then I will try that.

[pschatzmann]

I was just converting your example to 24bit and I am getting the expected result

[wegscheider]

Great, got everything to work now. However the 24bit input from the microphone didn't work but 32 bit and a VolumeStream, then conversion to 16bit did the trick!