為何SDM ADC 第一級anti-alias filter cut off frequency 是20K

aaaach

為何SDM ADC 第一級anti-alias filter cut off frequency 是20KHz??
4 c3 H8 m7 z9 y8 |' q通常audio digital output sample rate is 44.1/48/96/192KHz
but the first anti-alias filter in analog SDM ADC input is 20KHz
if your sample rate is 192KHz, its fs/2 is 96KHz, 20KHz~96KHz will be attenuated by anti-alias filter
what is the difference with 48/96/192? the signal information is only under 20KHz.
who can tell me what is the difference in this condition?
4 b$ h2 u( }9 Qand is it really used 20KHz as the anti-alias of SDM ADC for audio?

aaaach

原帖由 monkeybad 於 2008-12-23 11:27 AM 發表
& T$ n" A; F0 S雖然SDM ADC是用192K當作sample rate, 但是要處理的聲音信號還是在20K(這是人耳廳的到的的頻寬)
8 C, a0 {! v( u( R8 h( o6 bSDM ADC是用over sampling的技巧讓SNR提高, 所以sample rate通常會比信號的頻寬要大上許多倍

20K is the BW of human hearing,
what is the difference of 44.1/48/96/192KHz data sample rate in audio when this signal is over 20KHz?
SDM ADC uses over sampling for gaining high SNR. the oversampling rate will be 64/128/256 fs.
the fs is 44.1/48/96/192KHz.
SDM ADC with over sampling rate is right point, but sample rate didn't have direct relation with SDM.