Matrix recalc speeds

Sooo... Since I realised that the matrix recalculation takes too long, I did some quick calculations and a tiny fix.

By changing the matrix accumulator from an int64_t to an int32_t, I got a reduction from 81us/loop to 48us. Looks like this fixed the envelope "jitter".

Then I started looking at how much happens during recalculation.

We do a staggering 2719 iterations over various params. If we assume that we can achieve 600 instructions every us (600MHz), and we do 12000 loops every second, we have 600 000 000 / 12 000 = 50 000 instructions available to us per loop. Divide this by 2719 iterations.and we end up with 18 instructions per param calculation. That is WITHOUT taking into account everything else that happens during that time, like calculating envelopes, updating the S&H buffers and writing to the DAC.

This is surprisingly low. I am not sure I can make it work but it makes for a great challenge! I should really start looking into more efficient matrix multiplication. 

Update:

Removing amount != 0 checks, e.g. calculating ALL possible params all the time, makes the loop time jump from 48us to 105us.

But then, replacing / 32767 with >> 15 (/32768) brings the time down to 71us. We do get a tiny accumulated error here, I need to check the implications. But it means the worst case scenario is 71us/loop if everything is modulated all the time (?). Still too much, but not as bad as expected. Combining >> 15 with still having the amount check will be the best solution for now.

Not updating envelopes after calculations dropped from 48us to 31us, so we should definitely check for changes before updating.

Things to try: Swapping ints for 32 bit floats and using range [-1, 1]. Means we don't have to divide/shift every calc.

Inline array lookups instead of using variables (though the compiler should figure this out...)

Update 2:

Adding a check for each destination to see if it is necessary to calculate the matrix brought the time down from 48s to 11us (but this will get progressively worse when more things are dynamically modulated). 

Should also add a check to see if env/lfo params have changed before actually updating, as this is a costly process.