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dCS 954 User Manual Manual for Standard Software Version 1.5x
dCS Ltd June 2000
Manual part no: DOC136954 iss 2B1
Page 47
file 135954ma2b1.pdf available from website
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Frequency Response
The overall frequency response is determined by the sample rate, the digital
filter and the analogue filter. If imaging is to be avoided, all filters must cut-off
before Fs/2 is reached, with a margin to allow for sufficient attenuation to be
reached to effectively eliminate Nyquist images.
At a sample rate of 44.1kS/s, a flat 20kHz pass band must be maintained with at
least 80dB of attenuation above Fs/2 (22.05kHz). This allows barely 2kHz
margin between the pass band and the stop band for the filter to do its work,
necessitating a very sharp filter.
At sample rates of 88.2kS/s and above, there is so much extra bandwidth
available that maintaining a flat 0 - 20kHz audio band is less of a problem. This
allows more relaxed filters to be used, resulting in extra sonic benefits.
Frequency responses for all 7 PCM sample rates, set to Filt1, are shown below.
Filter 1 Frequency Responses
dCS 954
SW v1.30
-24
-18
-12
-6
0
6
0.02 10 20 30 40 50 60 70 80 90 100
Tone Frequency (kHz)
Level (dB)
192k176.4k
96k
88.2k
48k
44.1k
32k
DSD
Figure 27 – Filter 1 frequency responses