AutoAnalogAudio Library & I2S Output Now Working on nRF52840

 AutoAnalogAudio Library & I2S Output Now Working on nRF52840

Playing around with high quality audio on the XIAO Sense 52840

Its been a while since my last post regarding I2S audio on the nRF52840, but I finally got it working!

It came down to too small of buffer sizes, plus incorrect pins used for the MAX98357A breakout board. Now that the main problems are figured out, I have it working. There are still some issues with buffering, as there are small clicks or pops here or there throughout playback if the buffer sizes are too small.

To get it working with the current code from GitHub users need to enable I2S by calling the begin(); function a little differently:

aaAudio.begin(0, 1, 1);  //Setup aaAudio using DAC and I2S

This example enables the 'DAC' output using I2S within the AutoAnalogAudio library.

Valid sample rates have now been modified to standard sample rates: 16kHz, 24kHz, 32kHz & 44kHz. These are the only accepted sample rates.

I've decided to leave the PWM output as the default behavior since it is simpler in nature, gives good results and works OK with smaller buffer sizes. This is important when transmitting or receiving audio over radio link, since you need pretty large buffers with I2S.

Users can set the I2S pins prior to calling the begin() function for other boards that use different pins.

aaAudio.I2S_PIN_LRCK = 28;

Default Arduino Pin-Out for MAX98357A on XIAO Sense 52840:

BCLK: D1 (P0.03)

LRCK: D3 (P0.29)

DIN: D5 (P0.05)

SD Pin needs to be set HIGH for left output

GAIN: VIN

Use buffer sizes from 3200 to 6400 samples with higher sample rates / bit-rates.

AutoAnalogAudio Arduino library updated with ESP32 Support

 AutoAnalogAudio Arduino library updated with ESP32 Support

ESP32 DAC/ADC Output/Input via the I2S peripheral

Previously this year, I received some ESP32 based MCUs with OLED displays from DigitSpace, and used these devices to add ESP32 support to the AutoAnalogAudio library. It is a bit different from previous iterations, since instead of AVR interrupts and PWM, the ESP32 uses much more advanced peripherals. The I2S capabilities of the ESP32 provide a fairly seamless interaction when in/outputting audio signals, since it is just a matter of configuring the I2S, DAC and/or ADC and feeding and/or drawing data from the device. The main challenge in this case was combining the I2S functionality with RTOS tasks to provide a simple, asynchronous audio interface as is the case with the AutoAnalogAudio library.

The capabilities are much the same, but the ESP32 portion is still a bit in development, although working nicely at this point. The ESP32 example is specifically for the ESP32 device, since some minor API changes were required to manage RTOS tasks in combination with the I2S peripheral. This allows asynchronous handling of audio, so users can start playback and manage other tasks however desired while audio playback occurs.

Hardware:

1 x ESP32 OLED Wifi Kit
1 x MAX9815 Microphone Preamp
1 x TDA7297 PA Module

The MAX9815 will provide some audio to sample, and the TDA7297 was used to amplify the output of the onboard DAC. The above hardware as mentioned is provided by DigitSpace.

Connecting the Hardware:

With the ESP32, the AAAudio library samples the ADC on analog channel 4 by default, and sound output is on DAC1 and/or DAC2 (See previous post for pinout) The ADC channel cannot currently be changed, but that is on the to-do list.

Limitations:

The ESP32 onboard ADC will provide relatively good quality audio sampling, at 12-bits. The onboard DAC however, is only 8-bits, so the output will not be quite as high quality as with the Arduino Due. Using a higher sample rate can make up a for the low bit-rate of the DAC, as higher sample-rate * bit-rate = quality.

Overview:

Updating the library for ESP32 support has been fairly interesting, as it required a fair bit of learning and development time to understand I2S and how to control the related peripherals, while providing the same or similar behavior as with currently supported devices like the Due or Uno.

All in all it seems to perform pretty well. Audio input or output from virtually any source can be managed via the AAAudio library.

The updated library has been released and should be available via the Arduino Library Manager.

Source Code: https://github.com/TMRh20/AutoAnalogAudio
Documentation: http://tmrh20.github.io/AutoAnalogAudio

ESP32 - Playing around with the I2S peripheral and DAC audio output

 ESP32 Arduino - Playing around with the I2S peripheral, ADC and DAC audio output

 In some of my last posts, I mentioned the ESP32 based boards I recently received from DigitSpace, and I finally found some time to play around with some of the audio based peripherals. In this case I'm starting small, attempting to create a simple sine wave output using the internal DAC.

The documentation for the I2S peripheral is a bit limited it seems, but there is enough information in the Arduino Github repo to make sense of things and get some basic audio output going.

The general theory seems to be pretty simple compared to working with previous libraries, TMRpcm and AutoAnalogAudio, which utilize timer driven interrupts and nested interrupts (AVR devices) to handle asynchronous audio processing. The ESP32 provides a number of methods to handle audio processing, with peripherals designed to offload this work from the central processor, making the user interface mostly about buffering and handling audio data.

I've put together a simple outline of the code on GitHub.

The above code will produce a simple sine wave output on the DAC pins (see previous ESP32 related posts for pinout) and can be toggled off/on by entering a '1' on the Arduino Serial monitor. An audio file can also be defined and played by entering a '2' in the Serial monitor. In this case the sketch is setup for a 32Khz, 16-bit, Mono audio file.

In this case the hardest part is following the documentation found above and figuring out just how simple it actually is to handle the I2S peripheral. Really, you just configure the appropriate sample rate and output pins, mode etc, and then feed data into the peripheral. If doing any digital signal processing, its really about providing enough CPU time to handle the data and feed it into I2S. If handling audio files, the hardest part is decoding.

This should prove to be a good basis for the AutoAnalogAudio library since the only thing left to do is add ADC support and either use timers or RTOS tasks to handle asynchronous processing of the audio.

New Sampling/Audio library for Arduino : AutoAnalogAudio

Easy access to the internal DAC(or PWM), ADC, Timers & DMA for sound generation

I've been playing around with the Arduino Due for a while now, and finally got to looking over the datasheet and playing around with some of the internals because of ongoing requests regarding audio functionality and advanced timer usage etc.

As a result of my dabbling, I've created a sampling library to simplify access to the onboard Analog-to-Digital (ADC), Digital-to-Analog (DAC), Timer and DMA peripherals.

It is a simplified API that allows users to create a wide range of audio or related applications in short order.

Auto Analog Audio (Automatic DAC, ADC & Timer) library

Goals:

Extremely low-latency digital audio recording, playback, communication and relaying using a simple API

Features:

• New: Now supports AVR devices (Uno,Nano,Mega,etc)
• Designed with low-latency radio/wireless communication in mind
• Very simple user interface/API to Arduino DUE DAC, ADC, Timer and DMA
• PCM/WAV Audio/Analog Data playback using Arduino Due DAC
• PCM/WAV Audio/Analog Data recording using Arduino Due ADC
• Onboard timers drive the DAC & ADC automatically
• Automatic sample rate/timer adjustment based on rate of user-driven data requests/input
• Uses DMA (Direct Memory Access) to buffer DAC & ADC data
• ADC & DAC: 8, 10 or 12-bit sampling
• Single channel or stereo output
• Multi-channel ADC sampling
• AVR devices with no DAC or DMA use pseudo DAC(PWM) & DMA(Timer + Memory Buffer)

Testing:

The results so far have been very good. Using the nrf24l01+ radio modules, I was able to stream a standard format *.wav file of high quality (48khz, 16-bit, Stereo) from a Raspberry Pi to the Arduino Due using a slightly modified version of the included Wireless Speaker example.

To put that in perspective: Data Rate = Sample Rate * Channels * BytesPerSample

Streaming over Radio (RF24):
Data Rate = 48,000 * 2 * 2 = 192.0KB/s 

Streaming from SD Card:
Data Rate = 44,100 * 2 * 1 = 88.2KB/s (maximum rate with noticeable slowdown)

Using an SD card is a bit less exciting, as the audio starts to slow down noticeably with audio of 44.1khz, 8-bit, Stereo. Unfortunately, the SD speed is currently a bit limited, since the HSMCI is not available on stock Arduino Due, and I haven't found a faster working library like sdFat for Due.

SdFat Lib:
The sdFat library works with the due, I just had to initialize it at SPI_DIV6_SPEED (10.25Mhz SPI), and it worked using a value of 5 (17mhz SPI) as well. Initial tests show the max read speeds with the stock SD library at about 113KB/s, and 182KB/s with sdFat lib. Adjusting the SdFatConfig.h file to set ARDUINO_FILE_USES_STREAM = 0 results in speeds of 204KB/s with my current card & module.

These numbers indicate that the Due can handle quite a bit of punishment, and is easily up to the task at hand. The main limitation seems to be the throughput of whatever device is providing the audio or recording it etc.

Initial testing on AVR devices seems to indicate functionality similar to my RF24Audio and TMRpcm libraries.

If using a faster device, or generating audio from tables stored in memory, it seems that the Due with the AAAudio library will most likely handle it.

Notes:

If using the RF24 library in combination with an SD card, I highly recommend using a separate SPI BUS for the radio and SD card. I experienced a number of problems with high speed transfers etc when attempting to extend the length of wires used or connect an SD card module as well.

See the SPI_UART library section of the RF24 docs to enable a secondary SPI BUS for the radio.
Due Pins - TX1: MOSI, RX1: MISO, SDA1: SCK, CS&CE: User selected



Installation: AutoAnalogAudio is available via the Arduino Library Manager


I've also included a number of examples that demonstrate usage:
Click: File -> Examples -> AutoAnalogAudio in the Arduino IDE

SDAudio Examples: Demonstrate how to play back and record WAV/PCM format audio from SD card using the AAAudio library

Wireless Examples: Demonstrate receiving and sending streams of audio data via nrf24l01+ radio modules and are easily modified to work with other radios or devices. Some matching examples and audio samples are included for Raspberry Pi.

Audio Generation Examples: Demonstrate playback of simple audio tones or synthesized audio.

ADC/Audio Capture Examples: Demonstrate how to capture data/audio streams from the ADC on one or more pins/channels.

Documentation: http://tmrh20.github.io/AutoAnalogAudio
Source Code: https://github.com/TMRh20/AutoAnalogAudio