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Sat May 17 14:01:03 EDT 2014

Audio scale units

Following chuck moore's advice: pick good units!

Trying to get a good idea of units for audio synth applications.

Order of magnitude: 20mA, 20kHz, 2.2mV (sawtooth from current through cap).

These seems proper units:

mA
kHz
V
uF
kOhm

Derived from main equation:
C = I / f V  
-> uF = mA / kHz V     (/ 0.001 (* 1000 1)) = 10E-6 

So caps are in the nF-uF range, with impedances of:

                              Ohm from Hz, F                 kOhm from kHz, uF
20kHz -> 17 Ohm      (/ 1.0 (* 6.28 20000 0.00000045))  (/ 1.0 (* 6.28 20    0.45))
20hZ  -> 18 kOhm     (/ 1.0 (* 6.28    20 0.00000045))  (/ 1.0 (* 6.28 0.020 0.45))


So typically nA and pF range parasitic values can be ignored.  Those
are important mostly for MHz applications, not kHz.


EDIT: Let's try that out on a diode ladder computation:
f = 1 / 2 pi R C
R = V_T / I
=>
f = I / 2 pi V_T C

   mA        mV uF     kHz
(/ 1 (* 6.28 25 0.33)) 0.019







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