[PD] Acoustic conversions : formulas?

[Miller Puckette]

Hi all,

pitch = 69 + 12 * log_2(frequency/440) = 69 + (12/log(2)) * log(frequency/440)

frequency = 440 * exp(log(2) / 12 * (pitch - 69))

It's calculated (in slightly streamlined form) in x_acoustic.c .

"rms to db" is:

db = 100 + 20 * log_10(rms)

and so on.

cheers
Miller

On Thu, Jul 18, 2002 at 04:48:26PM -0600, David Sabine wrote:
> Hello all,
> 
> Can somebody tell me what formula is used in PD to convert MIDI to frequency?  (i.e. how does [mtof] REALLY work?)
> 
> Is it a table? or a formula?
> 
> By the same token, I'd like the formulae for [ftom], [dbtorms], [rmstodb], [dbtopow], and [powtodb] as well.
> 
> Regards,
> Dave Sabine