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ESP32AudioFramework

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Dual core concurrent multi-task processing of continuous real-time audio on the ESP-32

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### Dual Core Audio Framework for ESP32
Proof Of Concept Demos:
Dual core concurrent multi-task processing of continuous real-time audio
on the ESP-32.

Tested on Espressif ESP32 Dev board
Rev. 1 silicon

Arduino IDE with the ESP32 core from espressif

ADC/DAC sample processing at 8Ksps for voice audio range (< 4KHz).
Not suitable for music as is.

Core 1 -- Sample Service

Core 0 -- Application Processor

Cores use alternating ping-pong buffers to pass samples between them every
N samples. Tasks synchronize on a "FrameAvailable" semaphore.

Frame processing
runs every N samples on the Application Processor. The Frame processing technique
introduces latency delay (audio input to output).

Concurrency examples include:
* Continuous sine wave
* Dual tone (frequencies re-create old telephone dial tone)
* Continuous phase frequency sweep test signal (300--3000 Hz in 5 sec.,repeated)
* Microphone talk-through
* Pink Noise example from portaudio.com
* Voice Alert Example
__________________________________________________________________

I'll add more Digital Signal Processing examples to test the limits of this
framework. And maybe find some optimizations.

bobolink
twitter: @wm6h

__________________________________________________________________

ref:
esp32 arduino ide
https://github.com/espressif/arduino-esp32

Sensorsslot's ESP32 Arduino IDE Dual core multi-tasking intro:
YouTube video: https://www.youtube.com/watch?v=k_D_Qu0cgu8
 http://esp32.info/docs/esp_idf/html/dd/d3c/group__xTaskCreate.html

some watchdog info:
 https://github.com/espressif/arduino-esp32/issues/595

You can do Digital Filtering with a MCU
YouTube https://www.youtube.com/watch?v=k0LHp6jtHA8

High-Voltage Signal Conditioning for Low-Voltage ADCs
http://www.ti.com/lit/an/sboa097b/sboa097b.pdf

Audio Out Circuit.

The PAM 8403 uses 5VDC from the ESP-32 Dev Board.
Output is on DAC1 GPIO pin 25 of the ESP32
No DAC re-construction filter is used.
Some aliasing on the sweep app is heard at high volume. Maybe a re-construction
at the DAC output would help.

Audio In circuit: SparkFun Electret Microphone Breakout BOB-12758
https://www.sparkfun.com/products/12758
It has a freq. response to 10KHz and we sample at 8Ksps so a pole is added to
its response to turn it into a 1st order (20 dB/Decade power drop-off)
anti-aliasing filter (LPF) with 4KHz cutoff
Add a 47pF cap across R5 (820K). From JP1-3 to U1-4 is easier.
We would like a 2nd order filter here (40 dB/Decade power drop-off).
 https://cdn.sparkfun.com/datasheets/BreakoutBoards/Electret_Microphone_Breakout_v20.pdf

note: this circuit could be avoided by sampling at 16Ksps

mic audio is on analogRead(34)
ADC_WIDTH_9Bit to more or less match the DAC 8 bits.
An ADC_ATTEN_11db pad is set in order to run the mic at 3.3 Volts

3/10/18 Pink Noise example from portaudio.com modified for ESP32 Audio Framework. Statistics haven't been verified with spectrum analyzer.

3/15/18 modified sine generator with nkolban's BLE library. Select freq of sine over BLE (30-3000 Hz UTF-8 
unsigned int string < 5 chars).   https://youtu.be/MGNU7COFlT4

3/21/18 Voice Alert example. Audio samples stored as an array in the source. File edited in Audacity (Audacity.com) and saved as mono, 8Ksps, signed 16-bit PCM Microsoft WAV file. Converted to C source with xxd -i fn.wav fn.c

3/24/18 Project completed and Summary.md posted.

![BlockDiagram](https://raw.githubusercontent.com/bobh/ESP32AudioFramework/master/ESP32AudioFrameworkBlock.png)
# ESP32_AudioFramework

ESP32AudioFramework

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