esp-idf/examples/peripherals/i2s_adc_dac/README.md

# I2S built-in ADC/DAC Example


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* This is an example of:
    * Recording sound from ADC
    * Replay the recorded sound via DAC
    * Play an audio file in flash
    
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* Run this example
	* Set partition table to "partitions_adc_dac_example.csv" in menuconfig, or rename sdkconfig.default to sdkconfig directly.
	* Set IDF_PATH and run "make flash"
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* This example will execute the following steps:
    1. Erase flash
    2. Record audio from ADC and save in flash
    3. Read flash and replay the sound via DAC
    4. Play an example audio file(file format: 8bit/8khz/single channel)
    5. Loop back to step 3
  
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* Hardware connection:

  | ESP32 | Microphone + amplifier | amplifier + speaker |
  |--|--|--|
  | GPIO36(ADC1CH0 input) | data output pin |  |
  | GPIO25(DAC1 output) |  | right channel speaker input|
  | GPIO26(DAC2 output) |  | left channel speaker input|

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* How to generate audio files:
	
	* tools/generate_audio_file.py is an example of generate audio table from .wav files.
	* In this example, the wav file must be in 16k/16bit mono format.
	* generate_audio_file.py will bundle the wav files into a single table named audio_example_file.h
	* Since the ADC can only play 8-bit data, the script will scale each 16-bit value to a 8-bit value.
	* Since the ADC can only output positive value, the script will turn a signed value into an unsigned value.
	
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* Note:
	* DAC can only play 8-bit data, so the wav file data are scaled to 8-bit data.
	* I2S DMA can only output 16-bit/32-bit data to DAC, DAC will only take the highest 8-bit data and output accordingly. 
	* Before I2S DMA can output data stream to DAC, the data format should be converted to 16-bit or 32-bit by padding zeros.