The linking between physical book and digital book is somewhat reminiscent to me to Livescribe.com's use of Anoto digital paper and direct linking of handwriting on the page with recorded audio. Perhaps the physical book and digital book could use such a substrate to effectuate some of the work seen here, but also do it in a way that is easily (digitally) recordable as well as replayable. They've also done some of the handwriting to text work one might want in this space.

reply to Sascha at https://forum.zettelkasten.de/discussion/2583/tipps-for-purchasing-a-dictation-device#latest:

I've got an older Livescribe Pulse pen I love with a small pocket notebook or Post-It Notes. It has an optical character reader and special paper but also records audio and links it to the written text (either before or after the fact). I primarily use it for longer lectures where I'll take scant notes, but have the ability to add to them based on the recorded audio later. They've also got some 3rd party OCR solutions that will take your handwriting and convert it to digital text later. While they do larger sized notebooks and a variety of other papers as well (including printing your own), the small pocket size and ease of use has been fantastic. I've owned one version or another for more than a decade and really love them for this sort of audio on-the-go functionality. Since it's a digital pen, it's also unobtrusive in meetings. The added ability to share pdf documents with embedded audio after the fact isn't bad for classmates or meeting attendees.

Digitize your notes: Step by Step Using Neo Smart Pen https://www.youtube.com/watch?v=Otj3x_9h2RM

Nothing brilliant. the Neo Smart Pen looks like a direct competitor to Livescribe with Anoto paper

I've used Livescribe pens/paper for note taking (including with audio) before, and they've got OCR software to digital workflows. Or for the paper motivated, one could use their larger post it notes and just stick them to index cards as a substrate for your physical ZK with digitally searchable back ups? Now that I've thought about it and written this out, I may have to try it to see if it's better than my prior handwritten/digital experiments.

https://www.myscript.com/