Espressif Systems (Shanghai) CO., LTD

Espressif Audio Development Guide

Ai-Thinker Co., Ltd.

A.I. ESP32-Audio-Kit
A.I. ESP32-A1S
ESP32-Audio-Kit Wiki (not found)

ESP32-A1S I2S/PCM Audio Interfaces Stereo

X-Powers AC101, I2S/PCM Audio Interfaces Stereo CODEC with Capless Headphone Drivers for Portable Audio Applications

Maxim Integrated

Audio
MAX98357A, Tiny, Low-Cost, PCM Class D Amplifier with Class AB Performance

Texas Instruments Incorporated.

Speaker amps that drive big, clean sound
TLV320AIC23B, Low-Power Stereo CODEC with HP Amplifier

Analog Devices, Inc.

Class D Audio Amplifiers: What, Why, and How

Wikipedia

Class-D-Verstärker
I2S

Tutorials

I2S Sound Tutorial for ESP32
mikrocontroller.net ESP32 A1S Eval
ARM MP3/AAC Player
I2S
ALL YOU NEED TO KNOW ABOUT I2S
Audio acquisition with Espressif ESP32 WROOM and WROVER modules

GitHub

github.com/espressif/esp-adf
github.com/phkehl/esp32-a1s-audio_hal
github.com/donny681/esp-adf
github.com/pschatzmann/ESP32-A2DP
github.com/Ai-Thinker-Open/ESP32-A1S-AudioKit
github.com/Yveaux/AC101
github.com/schreibfaul1/ESP32-audioI2S
github.com/biologist79/Tonuino-ESP32-I2S
github.com/Edzelf/ESP32-Radio

Schematics

ESP32-Audio-Kit Schematics (PDF)
ESP32-A1S Module (PDF)