Such a great topic, the choice of 70 as in Music70 that is.
I personally associate the meaning of 70 with the following:
1. There are 10 octaves in the audio spectrum of human hearing, from 20Hz to ~21,000Hz. In a diatonic scale (e.g., C Major) each octave has 7 notes. So, [(7 notes per scale) * (10 octaves)] = 70 total notes within the the human hearing spectrum.
In this context, 70 would refer to completeness, all parts being accounted for in the sound from 20Hz to 21,000Hz. The 42Hz punch on a kick drum, the 428Hz melodic element, the distortion-saturated Return channel starting at 17,500Hz, etc. They've referred to envisioning the track as a "crystal" before in interviews, so shaping every element of the sound as perfectly as possible connects to this idea of geometric completeness, related to the 70 spaces for discrete notes in the audio spectrum.
Of course it might not be what BoC had in mind specifically; I just thought it was interesting.
2. This one gets a bit out there, but it is pretty mind-bending. The proportion 0.70 is a meta-attribute of the various relationships between the semitones making up an octave, when using a root note as a reference point.
Here is a list of the ratios the 12 notes comprising a standard chromatic sequence, relative to the root note:
step 0: 720 : 720 (1 : 1) [this is the root note]
step 1 : 768 : 720 (16 : 15)
step 2: 810 : 720 (9 :
step 3: 864 : 720 (6 : 5)
step 4: 900 : 720 (5 : 4)
step 5: 960 : 720 (4 : 3)
step 6: 1024 : 720 (64 : 45)
step 7: 1,080 : 720 (3 : 2)
step 8: 1,152 : 720 (8 : 5)
step 9: 1,200 : 720 (5 : 3)
step 10: 1,296 : 720 (9 : 5)
step 11: 1,350 : 720 (15 :
step 12: 1,440 : 720 (2 : 1) [this is the octave]
You see I re-factored each proportion to out of 720 because that common factor could represent all the proportions, making it easier to understand the relationships between them. And that is where 0.70 can be found.
As a side note before going on, since you can express any musical ratio out of 720, that idea seems to fit nicely with the idea of "Twoism", because 720 also represents two circles. Kind of cool, just a thought anyways.
So back to the 0.70. First thing to do is look at the amount that each proportion relative to 720 goes up. The first semitone goes from 720:720 (duh) to 768:720, a total increase of 48:720. The next semitone goes from 768:720 to 810:720, a total increase of 42:720. Going through the whole chromatic octave results in the following array of respective increases :
semitone_increase_list = [48, 42, 54, 36, 60, 64, 56, 72, 48, 96, 54, 90]
SO, here's where, as I said, it gets "meta".
Due to the fact that every proportion is relative to 720, we can have a meaningful look at the changes between the proportions of notes. In other words, since all the above numbers in "semitone_increase_list" are relative to changes out of 720, we can look at their differences as meaningful.
The difference between notes, or the delta_notes array, is as follows:
delta_notes = [-6, + 12, - 18, + 24, + 4, - 8, + 16, -24, +48, -42, +36]
sum of negatives in delta_array: 98
sum of positives in delta_array: 140
proportion of negative growth to positive growth: 98 : 140 or 0.70 : 1
I think it's pretty beautiful that there's an oscillation between positive change and negative change in the delta_notes array. It seems we humans have an idea of where the notes should stay. And as BoC have mentioned in interviews, there's enough sunlight for that leaf, for that individual note to grow there.
Anyway I'm getting off topic!
dude how did you find this video of me 
