It seemed like an impossible task. To get more the two audio channels into and out from the Pi over the GPIO header. Lots of people wanted that functionality but no one could work out how to do it. I decided this product would have the potential to completely enable and transform other peoples projects. Not only, that if it could be done on the Pi, it could be done on most other embeded boards. It would empower people by solving what seemed impossible. Beyond that, the outcomes for the developing world would be to put an ultra low cost multitrack recorder into the hands of people who otherwise may never be able to afford it - a sub $150 professional grade multitrack recorder. Who knows what people would invent with it !
I put together a plan and began hacking from paradigm to paradigm, making small incremental steps. It felt like I was building a rocket going to the moon for the first time ! No one ever thinks of low level hardware/software hacking as sexy, so it never makes the news
After months and months of struggling, first with purely analogue electronics, ECL logic and all sorts of tricks, I got really close. Sooo close I could sense the signals were going in the right direction - it just needed a little more. But that little more certainly wasn't going to come from analogue electronics alone. I had to change directions.
I decided to learn VHDL and started using FPGAs. On the weekends, whilst guarding my daughter's infant sleep cycles, I would read free range VHDL on my phone or laptop, gradually grasping this non procedural way of "the hardware". Finally after months, at the digital hardware level, I was able to get 8 channels of audio into and out from the Pi hat. Eureka! It is incredibly reliable. So functionally attractive and reliable that it had to be let out of the box ! And so it began ....
Come join the fun and checkout the Audio Injector Octo Pi kickstarter.
p.s. It is arguable that $150 is still well out of reach for a lot of people in developing nations.