Cool. AK CODECs sound very nice, sometimes even better than Cirrus chips.

Some years ago I did a similar board hooking an STM32F4 to a TLV320AIC3256 CODEC. TI provides an audio development IDE, PurePath [0], to program the embedded miniDSP where you can 'code' and configure different effects graphically (they even have a guitar FX demo, tool written in LabVIEW - yikes!).

Sadly they don't disclose the low level programming instruction codes, therefore changing things programmatically in the microcontroller at runtime is limited. I tried to reverse engineer the instructions with limited success, and then I just lost interest. ¯\_(ツ)_/¯

[0] http://www.ti.com/tool/AICPUREPATH_STUDIO

Very nice. Also check out ELK which is a much more ambitious such project. Https://elk.audio

I'm not sure how this is better than a raspberry pi. $5 more would get you a lot more power.

My understanding is that for audio the bit resolution of the A/D is crucial. Also looks like they have put together a system that not only can get a good sample but enough of them in some amount of time that it is usable and of some quality.

Not only that, audio CODECs have analog filters designed specifically for audio capture and reproduction, sometimes even configurable.

The advantage of having a cheap tiny board is that you can build a system like a polyphonic synth with very capable voices with relative ease. And since each one has inputs too, you can interconnect signals giving a lot of flexibility (aka modular synth).

A lot more power, yes, but also a lot more to worry about. It's a plus if you don't have to manage an entire OS. It would also probably need a lot more watts than this little board.