f4uac

F4UAC – USB Audio Class headphones on STM32 MCU (-ish)

Wait, what ? Again ? sigh yeah, again.

Abstract

Loose implementation of excellent ST appnote AN5142, using so-called Black Pill boards.

Description

So, USB audio on STM32. Usually this involves USB-I2S bridge, some DAC, and maybe power stage on cheap D-class chip. Boring. Let’s do it in software (and hey, check that paper above, really).

(back ? good)

Audio data flow:

As one can see, while overall scheme remains the same, some (let’s call it) improvements exists:

• S16/S24/S32/[email protected]/48kHz and S16/[email protected]/96kHz as input;
• optional subwoofer channel with crossover at 120 Hz;
• 8x/16x upsampler with 24/48-tap FIR interpolator;
• 4th order noise shaper;
• 7bit/384kHz PWM as output;

From USB poit of view, things are pretty straightforward:

Requirements

• arm-none-eabi toolchain, i.e. from here
• octave with
• octave-signal extension.

Quickstart

git clone --recurse-submodules
make

Precompiled binaries are in bin/ directory

Schematics

Resulting PWM outputs are GPIOA8/GPIOA9 for left/right channels, with complementary GPIOB13*/GPIOB14*. Sample schematics for headphones:

Another one, sort of ‘desktop speakers’:

Oh, and you can attach OLED display. Or two. And encoder. And proper power stage. Anyway, here’s latest:

Maybe i should consider title change.