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

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# I2S built-in ADC/DAC Example
---
* This is an example of:
* Recording sound from ADC
* Replay the recorded sound via DAC
* Play an audio file in flash
---
* 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"
---
* 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|
---
* 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.
---
* 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.