dCS 954 User Manual

Manual for Standard Software Version 1.5x

dCS Ltd

June 2000

 

 

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.

Level (dB)

 

 

Filter 1 Frequency Responses

 

 

 

 

dCS 954 SW v1.30

 

 

6

 

 

 

 

0

 

 

 

 

32k

48k

96k

 

 

-6

 

 

 

 

 

 

 

 

DSD

 

44.1k

88.2k

176.4k

192k

-12

-18

-24

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.02

10

20

30

40

50

60

70

80

90

100

 

 

 

 

 

 

 

Tone Frequency (kHz)

 

 

 

 

 

 

Figure 27 – Filter 1 frequency responses

Manual part no: DOC136954 iss 2B1

Page 47

file 135954ma2b1.pdf available from website

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