Very nice. Although this brings up lots more questions...
When I see your work, it is rather amazing. So I get the feeling that you have already practiced and defined each section of of the turtle shell in a sketchbook somewhere else. Each section of the shell is so detailed, all sections are very detailed as that is your style, so I am just using a section of the turtle shell as an example. But the details are so fine, it was originally very hard for me to think that you were doing this all on-the-fly. I felt that you already had an idea, you already had some patterns defined, so you just went to work at a larger scale.
However, here in this post, it nearly seems like you are designing all of this on-the-fly because you are discussing what comes out with different music.
Which is pretty amazing. In the video, it looks like you went back and erased once or twice. Perhaps that is just the video but that would lend itself to the on-the-fly theory about your method.
I suppose that if you are doing all of this on-the-fly, then my thoughts go into repetition. For example, I would think that you design one section of the shell on-the-fly, then if you really like it, you will replicate that to the other sections.
This is all just assumption and thoughts running through my head as I look at your work. You don't have to comment if you wish to keep this stuff secret. I will understand.
This turtle I actually drew on a smaller scale around 2 years ago :-) I felt it might have been have hindered the quality of the project trying to create a new piece whilst juggling trying out this new timelapse method. So I went with an older drawing I fancied doing on a larger scale and created it to fit with the song, drawing the parts that reflected that moment in the music... (This wasn't very clear in the post, so thank you for raising the question!) So I always start with the eye, then imagined the little patterns around the eyes emerging to the "tinkles" at the beginning of the song and had the dark netted part kind of "blurt out" as the music descended (wow, it is a lot harder to explain this in words than I thought!) The next step I'm now working on is combining the two and creating something brand new where the whole piece is based on the piece of music :-) It took around 3 months to finish this one, so I'm not sure how long it'll be until the next one's ready! But I've made a start.
There's a timelapse I made in a similar style featuring a new piece I freehanded straight to the wall, so all is possible! I've used the same basic outline for previous elephants, but not the same design :-)
And thank you for taking the time to write out such a thoughtful reply by the way, it's my pleasure to extend the same courtesy back to you. Followed and look forward to keeping in touch in future!