What is the maximum allowed transition band of the low-pass filter used in the reconstruction kernel for a CD with maximum speech frequency of 4 kHz? My question is if the transition band in the question below would be from 4Khz to the Nyquist frequency of 22.05Khz or from 4Khz until 44.1Khz-4Khz=40.1Khz?
If you don't want DAC noise near 40-44 kHz to alias down into your audio, you want the narrower/lower transition band reconstruction filter.