“ESP8266 has an ADC input which is a 10 bit analog to digital converter and this pin is the audio signal input for the “ESP8266 Audio Recorder” project.
This project is an arduino (c-language) source code, which is a firmware for the ESP8266 module and records the audio data by reading the ADC pin’s value, encodes the data and sends it to the web browser via the firmware’s Web Application.
The web browser saves the data and the user can play or download the recorded audio.
The audio signal must be between 0-3.3v for ESP32 and NodeMCU modules and must be between 0-1v for directly connecting to the ESP8266 modules.
The best compatible audio amplifier is LM386. The “WaveShare Sound Sensor” is using this op-amp and also you can use the suggested schematics in the manual file of the project.”