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: espressif/arduino-esp32#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.
