in sigma delta for audio applicaitons which input frequency should be taken for calculating SNDR. audio range 20 to 22KHz or so taking a Band Width of 25KHz which frequency to take.
Fin=Fs / 2^n to fit the input frequency in 20~~22K Hz.
EX: Fs=2MHz, Fin=2M / 2^9 = 3.90625KHz
you can find Fin=3.90625KHz ,Harmonic3 = 11.71875 KHz
so you can calculate SNDR
No, n is a arbitrary number.
use FFT function to calculate SNDR,
you can think a easy scale between fs and fin,
fs........32768
---=------------
fin........2^n
(if you want 32768 points)
so fin=fs*2^n/32768
if I do this ,I will choise n=multiple of 2, to fit fin below 22kHz