computationally efficient way of calculating envelope

[remedios_dream]

Hi all,

I'm doing a research about alternative ways of computing some basic shapes of envelopes (linear decay for now).

The mcu of my choice is stm32f401 (84MHz, fpu unit) and for now I handle 7 voices karplus-strong algorithm. I want to add at least decay to each of the voice but here comes the limitations.

For a linear decay I use this simple formula:

[Steveg]

Try using fixed point rather than floating point then you can use shifts to get the division. You'll want to use a buffer size that is a power of 2 as well.
if you are not familiar with "fixed point representation" you can google it, but it is a way of using integers to represent decimal values.
So you probably want to use an 32767 value array of 32 bit integers. To get the decay value right shift the integer by 15 ... in C
decay = value >> 15;
Possibly much faster than floating point (but occasionally not in processors with internal FP support) remembering each value has to be divided by 2^31.