I²S DACs

The Raspberry Pi's headphone jack is a simple PWM device, and not designed for high-fidelity audio. This becomes very obvious when you use mt32-pi - distortion in the sound is apparent when quieter sounds are playing.

Luckily, a plethora of inexpensive DAC (digital-to-analog converter) hardware is available for the Raspberry Pi, giving it true hi-fi quality audio output. These often take the form of an easy-to-install "HAT" board that you place onto the Raspberry Pi's GPIO pins. They make use of the Raspberry Pi's I²S bus for interfacing.

⚠️ Note: We do not support any kind of USB DAC audio output device, due to the lack of drivers in the Circle baremetal framework that we depend on. Adding USB audio support to Circle would be a huge undertaking, although if that changes in the future and Circle gains USB audio support, we could certainly make use of it.

Setup

• mt32-pi defaults to PWM (headphone) output. Edit mt32-pi.cfg and change output_device to i2s to enable the I²S DAC driver.
• If your DAC requires software configuration, you may need to edit the i2c_dac_address and i2c_dac_init options to suit your particular DAC. Continue reading for further details.

Compatibility

Currently, we have been targeting DACs based on the Texas Instruments PCM5xxx series of chips due to their popularity, but other DACs could be supported quite easily. The NXP UDA1334 is also reportedly working well.

Some more advanced DACs are configured by software (normally a Linux driver), whereas others need no configuration as they are preconfigured in hardware. This will vary between manufacturers, and so some editing of mt32-pi.cfg may be required.

⚠️ Note: If a DAC requires software configuration, they will not produce any sound until they have been properly initialized. This initialization is done by sending it a special sequence of commands over the I²C (not I²S) bus. For the PCM5xxx family, you can set i2c_dac_init = pcm51xx to enable this.

Feel free to open an issue if you'd like to help us support your DAC, or even just to report success or failure so that we can build a list of supported DACs.

The following models of DAC have been confirmed as working by our testers. Please note the necessary configuration file options.

Manufacturer	Device	DAC chip	Additional config file options	Comments
Arananet	PI-MIDI	UDA1334	None required	Stereo RCA output. Custom design by @arananet also with GPIO MIDI in. Tested by @dwhinham.
Blokas	Pisound	PCM5102A	Ensure sample_rate is set to 48000, 96000, or 192000	Stereo 6.35mm output, volume knob, and integrated SPI MIDI interface. Tested by @dwhinham and @sigkill.
chris-jh	mt32-pi-midi-hat	PCM5102A	None required	Stereo 3.5mm output. Custom free/open source design by @chris-jh also with GPIO MIDI in. Tested by @gmcn42.
Generic	GY-PCM5102	PCM5102A	None required	Stereo 3.5mm output. Found very cheaply on AliExpress and other sites. Tested by @dwhinham.
Generic	Pi-Fi DAC+ v2.0	PCM5122	i2c_dac_init = pcm51xx, i2c_dac_address = 4d	Stereo RCA and 3.5mm output. Tested by @rc55.
gmcn42	clumsyMIDI	PCM5102A	None required	Stereo 3.5mm output. Custom free/open source design by @gmcn42 also with GPIO MIDI in and out/thru. Tested by @gmcn42.
HiFiBerry	DAC+ ADC	PCM5122	i2c_dac_init = pcm51xx, i2c_dac_address = 4d	Stereo RCA output. Tested by @kgorphanides.
innomaker	HiFi DAC HAT	PCM5122	i2c_dac_init = pcm51xx, i2c_dac_address = 4d, sample_rate=44100	Stereo RCA and 3.5mm output. Not compatible with hd44780_4bit displays. Tested by @calvinmorrow and @alexras.
IQaudIO	Pi-DAC Pro	PCM5242	i2c_dac_init = pcm51xx, i2c_dac_address = 4c	Stereo RCA and 3.5mm output. Tested by @dwhinham.

Finding the I²C address of your DAC

The i2c_dac_address configuration file option determines what address on the I²C bus that mt32-pi will send initialization commands to, if i2c_dac_init is not set to none.

If your DAC does not appear in the compatibility table above, you can help by carrying out the following:

• Connect the DAC to your Raspberry Pi.
• Insert an SD card containing the latest version of Raspberry Pi OS (aka. Raspbian) and boot the Pi.
• Run the command sudo raspi-config.
• Select "Interfacing Options", followed by "I²C" and "Yes" to enable the I²C kernel modules.
• Exit raspi-config, and run the command sudo apt-get install i2c-tools to install some I²C utilities.
• Run the command i2cdetect -y 1. The output should be like the following:

       0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
  00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
  10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
  20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
  30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
  40: -- -- -- -- -- -- -- -- -- -- -- -- -- UU -- -- 
  50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
  60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
  70: -- -- -- -- -- -- -- --          
  

• In this example, the address is 4d. Make a note of this and set i2c_dac_address in mt32-pi.cfg.
• If your DAC now works, edit this page and add it to the table! Otherwise, open an issue, and we can try to work out how to support it.