[sdiy] Wavetable Design Update

[Matthew Smith]

Quoth Veronica Merryfield at 02/02/11 18:59...
> Use a spreadsheet to do it all with the percentage 
 > error, then pick the best. Should take about an hour
 > to get the formulas done then it's just about picking
 > the values.

Similar idea - I was guessing I was going to tackle this in Perl, 
building the rules as I saw what got spat out.

But this is the "static" method - would this mean that me picking values 
would mean that an on-the-fly calculation simply isn't feasible?

> Also, have a think about cutting the top end. The upper harmonic 
 > content will be from the sample rate and you won't need
 > anything about 20Khz. However, some say 10Khz is enough
 > in practise although midi note 127 is 12khz.

I'm only covering the MIDI note range, so 12.n kHz is the ceiling.

> If you have a low pass filter at 12Khz, a square wave would do 
 > for note 127 since the ear is not too good at hearing
 > 24Khz. However, this may be heresy to some :)

I know what you mean. I keep telling myself that I'm building a musical 
instrument, NOT a piece of laboratory test gear!

But changing the waveform dependent on frequency would add quite a huge 
complication to the design. As it is, the whole system is pretty 'dumb' 
- it just takes a note, generates a clock frequency of f*256, scans the 
EEPROM, outputs to DAC. Getting f is my biggest problem!

For reference, this is my note frequency lookup table generator:

www.smiffysplace.com/files/miditab.pl

...and this is the resultant .csv formatted with OpenOffice Calc:

www.smiffysplace.com/files/miditab.ods

If I need to do further calculations, I'll just tweak miditab.pl

Cheers

M



-- 
Matthew Smith
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