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??
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
% ^: K0 G! o7 \8 v3 |6 Lif 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?
+ w' Z! T: o: E, `+ dand is it really used 20KHz as the anti-alias of SDM ADC for audio?

ronnie710409

因為無論oversampling 64/128/256, 只要有oversampling, out-of-band noise就會alias到in-band, 所以無論你sampling rate多少的確跟AAF無關, 是跟你的in-band有關係而已.

netronix

因為人耳能聽到的聲音頻率大概在20hz~20Khz之間.
" R4 a7 v; J# G0 ]所以AAF要是signal bandwidth

lynker

SDM通过过采样来提高ADC的精度，但不可用采样频率/过采样率来理解输入信号带宽，尽管这个频率要大于输入信号带宽。
一般决定SDM SNR的因素有 SDM的结构 阶数 过采样率
1 S& O; g+ S3 t( t$ U& @在结构确定的情况下，可以根据性能要求来改变过采样率。

liangshangquan

AAF的cut off freq和sample freq無關，只和信號帶寬有關，音頻應用bw=20~20KHz，SO~~~

anita66

這問題也困擾我很久了,不知有沒有大大分享一下心得??或是再說明的詳細一點呢??3Q~

aaaach

原帖由 monkeybad 於 2008-12-23 11:27 AM 發表
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)
3 i* W* |9 y2 @+ E# G$ _& lSDM 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

0 z* W$ S% `/ ]( ]" v2 J
5 j# d# R% S. t1 C, I/ T! Y20K 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.
7 d1 K+ U$ m2 Zthe fs is 44.1/48/96/192KHz.
# a$ J6 o% m; |$ H0 m( ZSDM ADC with over sampling rate is right point, but sample rate didn't have direct relation with SDM.

李鐏鐶

因為人耳能聽到的聲音頻率大概在20hz~20Khz之間.

monkeybad

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)
1 n) D* I$ R! d5 s; }' zSDM 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