[sdiy] Frequency to MIDI Conversion

[Richard Wentk]

At 21:18 20/02/2003 -0600, MED wrote:
> >
>polyphonic:
>output sines for each note. FFT. Extract pitch. Wash, rinse, repeat. no?

No. FFTs aren't magic. They have issues like frequency resolution, and a 
tradeoff between resolution and frame sample rate. You'll also get 
frequency components being produced by (say) a step envelope, which an FFT 
will read as a transient with all possible frequencies. So you'd need to 
use the right envelope, do a lot of jiggling and fiddling to make sure your 
analysis routines are smart enough to bridge the gap between integer 
multiples of the analysis frequency, and so on.

I have seen this done. There's a freeware polyphonic pitch extractor for 
piano available online somewhere. But it's way more complicated to go down 
this route than to hack into the key scanning matrix  - an approach that 
will work in real time using very simple hardware and software, and give 
you instant accurate guess-free MIDI no matter what noises your synth is 
making.

Richard