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Old 19th February 2005, 12:43 PM   #21
sovadk is offline sovadk  Denmark
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I see. How do you explain the difference in SNR?
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Old 21st February 2005, 06:55 AM   #22
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There are several reasons IMO:

1.) Nothing ever works as good in practice as it should work in theory. If it really would, then the Sharp D-S amps would have a much better SNR than their 100dB (Theoretically 270 dB @ 20 kHz).

2.) The chosen dither is certainly not optimal.

3.) The chosen NTF may not be optimal either since I didn't spend too much time on detemining it. I just chose 200 kHz cutoff and fourth-order Butterworth for the NTF and then derived the coefficients for achieving it. This choice is quite critical: the lower the cutoff frequency - the worse the SNR, the higher it is (i.e. aggressive noise-shaping) - the more the loop is prone to instability.


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