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Converting the Data Format

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Phil Schatzmann edited this page May 4, 2024 · 23 revisions

I am currently providing quite a few audio processing classes which can be used to change the audio format.

You can use the more generic FormatConverterStream to change of the

  • bits_per_sample
  • number of channels
  • sample_rate

This class is supporting both: the conversion on the input and on the output side.

Converting on the Output Side

This is the recommended way and the propagation of changes of the AudioInfo should work automatically in all the cases.

#include "AudioTools.h"

SineWaveGenerator<int32_t> sine_wave;                   // 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);                         // Output to Serial
AudioInfo from(44100, 2, 32);                                           
AudioInfo to(44100, 2, 16);                                           
FormatConverterStream conv(out);
StreamCopy copier(conv, in_stream);                     // copies sound to out

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

  sine_wave.begin(from, N_B4);
  in_stream.begin(from);
  conv.begin(from, to);

  out.begin(to);
}

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

Converting on the Input Side

Here you need to be a bit more careful: If the input of the FormatConverterStream is an AudioStream you need to deactivate the automatic notification by casting the parameter to a Stream. This is necessary because the system can not know if you intend to use it as input (w/o notification) or as output (with notification)!

#include "AudioTools.h"

SineWaveGenerator<int32_t> sine_wave;                   // 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);                         // Output to Serial
AudioInfo from(44100, 2, 32);                                           
AudioInfo to(44100, 2, 16);                                           
FormatConverterStream conv((Stream&)in_stream);         // Define input and deactivate output notification
StreamCopy copier(out, conv);                           // copies converted sound to out

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

  sine_wave.begin(from, N_B4);
  in_stream.begin(from);
  conv.begin(from, to);

  out.begin(to);
}

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

Examples:

Final Comments

This class is very flexible and convenient to use. However if you need to save some milliseconds in your processing, it is a bit more efficient to use the dedicated class if you need to change only a single parameter: e.g. the sample_rate:

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