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
if your sample rate is 192KHz, its fs/2 is 96KHz, 20KHz~96KHz will be attenuated by anti-alias filter
  d" {& ~8 ~" g2 @" ~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?
! u- o5 r( L8 P4 {1 W+ Xand 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.
" m0 B: l. P! \5 R8 f8 b$ y* k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。
7 s6 b  i6 @! [4 d9 m" \+ p一般决定SDM SNR的因素有 SDM的结构 阶数 过采样率
* y4 J% C. c! r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)
SDM 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.

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)
SDM 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