[sdiy] semitones from dividers...Electronotes idea

[dan snazelle]

I was reading Electronotes today and something I read interested me but at the same time I am a bit stuck on how to implement it. It has to do with using logic to create
semitones.

Here is the text:

FROM Electronotes #70 page 12  (by bernie hutchins)  (3rd paragraph)


"the problem of non-integer division (usually by irrational numbers-to be approximated) comes up often in schemes to generate the tones of various musical scales.

in the equally tempered scale, the ratio of the semitone is 2 to the 1/12th power which is the irrational number 1.0594631...

which can be approximated by the rational fraction 196/185=1.059459......to an excellent approximation as can be seen.

Pulse drop-out methods can be used which drop out 11 pulses for every 196 by decoding a divide by 196 counter and blocking clock counts from reaching
the output."


There is a tiny digram which follows this information which simply shows a "divide by 196" box, which is connected to a bunch of lines and another box which is
 labelled "decoder for 11 of 196 states".  this connects to an inverter, which then connects to one side of an AND gate, the other side of which is connected to the same signal which drives the CLOCK IN of the counter.

I like the idea of being able to generate semitones from LOGIC but there is very little explanation of how to setup the decoding.

any ideas?

thanks!!