Tuttut:
Edit/New: I updated the library (ported the core output part to hand-optimized ASM) and now also 16 Bit audio output (even in stereo) is possible (combining two PWM outputs using 2 resistors, known as 256R-R-network).
You know about sigma-delta noise-shaping? Its not too hard to get high resolution out of a single 8 bit PWM
channel using it. Basically you shift the quantization noise up in frequency out of the audio band - its
closely related to dithering in 8 bit graphics.
How do you handle upsampling to 62.5kHz BTW?
For best results with sigma delta noise-shaping I'd suggest using 6 bit PWM so you can run PWM at 250kHz,
gives a lot more space to push the noise into, and its much easier to filter too.