DAM1021 NOS with a 3 Pole passive filter

[Ken Newton]

You are right. I always thought that the ideal DAC is the R-2R DAC, which perfectly restores the original signal and only adds the image spectrum. However, the result of the function calculation proves that its ZOH characteristic is indeed a function of (sinx)/x (X=f*pi/44.1k). Later I tested the FFT transform of the NOS AD1851 with a 200M digital oscilloscope. Even if the sampling rate is set to 2.5 MHz, 18 kHz also has about 2.5 dB attenuation. Calculated by switching the AD1851 to work at 44.1k and 192k sample rates. This attenuation is similar to a linear interpolation filter. Thank you very much for making me realize this mistake.

BR,
Mark

Mark, it's not easy for any of us to admit to an mistake. I respect your integrity and courage. Thanks.

By the way, the ZOH roll-off is problematic because it covers two full octaves, from 20kHz smoothly down to 5kHz. So, while -3dB@20kHz may not be audible, a frequency response masking contour spanning 20kHz to 5kHz is much more audible.

 

[Trajan]

I find -3db @18kHz as sounding completely unacceptable, aging ears or not. You really need a sinx/x filter for NOS or alternatively have to correct this in FIR.

I wonder if you know much about mastering music or have even seen much music on a spectrum analyzer. There is almost nothing typically at that frequency that you 'need' to hear.