dCS 974 User Manual

Manual for Software Version 1.0x

dCS Ltd

May 2001

 

 

DSD

Filter Options

DSD is a single bit very high sample rate (2.822 MS/s) format, where the single bit words are heavily noise shaped to push noise energy above the audio band. The frequency response is very high (well above 100 kHz) although at these high frequencies, noise is also present.

For SACD purposes, 0 dB0DSD is set at 6 dB below the peak to peak level one might expect a full scale sinewave to occupy – this ensures that artefacts that

begin to occur at the limits of the DSD amplitude range do not move down into the audio band. The 0 dB0DSD level is shown graphically in Figure 39, page 98.

The dCS 974 offers a number of different DSD modulators – as Filter options. All the modulators have the same signal frequency response. They differ in the way they shape the out-of-band Q noise, and in how far they suppress the in-band Q noise. Filters 1 to 5 suppress Q noise at least 120 dB below the nominal 0dB DSD signal, which is one of the marketing specs for SACD.

Filter

CommentsSQNRStabilityDescription

 

 

(20 kHz,

 

 

 

 

dB)

 

 

1

High SQNR, high stability

126.14

1.7*1010

Two complex

2

 

 

8.2*108

zeros

High SQNR

127.23

Two complex

3

 

 

1.5*1011

zeros

High SQNR, very high

124.66

Two complex

4

stability

 

3.0*1012

zeros

Extremely high stability

122.07

Two complex

5

 

 

7.1*1010

zeros

Reduced 100k noise

122.27

Two complex

6

 

 

3.7*1011

zeros

Single complex zero

110.78

Single

7

 

 

2.0*1010

complex zero

Real zeros

101.5

Real zeros

 

 

 

 

only

 

 

 

 

 

Table 4 – DSD Filter Summary

Signal to Q Noise and SACD Specs

Although 120dB SNR over the 0-20 kHz band is a good target, it does not match the ears response that well. The F weighted curve is currently accepted as a good model for the ear, and we can use this to weight the noise produced by the various filter choices. Such a weighting is shown in Figure 38 on page 98, and DSD gives very good performance using such a weighting (better than 23 bit pcm)

The figure shows that Filter 6 and 7 give more F weighted Q noise suppression in the audio band than Filters 1 to 5. Filter 6 gives around 20 dB more suppression than Filters 1 to 5 under all circumstances and Filter 7 gives 20dB more suppression below 10 kHz.

Manual part no: DOC1241121A1

Page 71

Document No: OS-MA-A0124-112.1A1

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