- I can add a DAC to the Voice controller and control it directly there - using a I2S Audio DAC will probably give a very high audio quality
- I can make a separate board with the same DAC, an extra MCU and external memory
- I can try to use the DCOs - they already have a 16bit DAC and I think I have exposed enough SPI pins to make it possible to access external SPI memory. This is the cheapest option but the sound quality must be tested.
In any case, when making the Voice board I should leave room for an optional wave card. It doesn't need its own VCA as the DAC should be good enough for volume control as well.
PIC32 and I2S Dac
It seems most Audio DACs these days use I2S for communicating with the host. The PIC32MX (and other low-end PIC MCUs) don't have I2S support built in, but here is something that seems to make it work:
https://www.aidanmocke.com/blog/2018/11/22/i2s/
https://hackaday.io/project/28965-pic32mx-music-box-with-fm-synthesis-and-i2s-dac
https://tutorial.cytron.io/2017/08/13/i2s-pic32mxmz-introduction/
DAC in general
DACs need a reconstruction filter to remove unwanted frequencies. Here is an example that claims to be good:
https://www.analogfilters.com/high-quality-reconstruction-lowpass-filter-for-digital-audio/
https://www.softwaredidaktik.de/active-filters/download/
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