DCS dCS 904 DSD, dB), SQNR, Filter, (20 kHz, Comments, Stability, Description, DSD Overview, Signal to Q Noise and SACD Specs

dCS 904 User Manual	Manual for Software Version 1.5x and 1.36
dCS Ltd	June 2000

DSD

DSD Overview

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 audio. The frequency response is very high (well above 100 kHz) although at these ultrsonic frequencies noise is also present.

The dCS 904 offers a number of different DSD modulators – as Filter options. All the modulators in 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	Comments	SQNR	Stability	Description
		(20 kHz,
		dB)
1	High SQNR, high stability	126.14	1.7*1010	Two complex
			8.2*108	zeros
2	High SQNR	127.23		Two complex
			1.5*1011	zeros
3	High SQNR, very high	124.66		Two complex
	stability		3.0*1012	zeros
4	Extremely high stability	122.07		Two complex
			7.1*1010	zeros
5	Reduced 100k noise	122.27		Two complex
			3.7*1011	zeros
6	Single complex zero	110.78		Single complex
	Real zeros	101.5	2.0*1010	zero
7				Real zeros only

Table 3 – 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 14 on page 35. 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 20 dB more suppression below 10 kHz.

SACD5 specifies ultrasonic noise in two bands. These are specs informative specs E2 and E3, and filter performance for a number of specs including these are given below. The measurements given have been made using a Fourier Transform based method.

5Super Audio CD System Specifications, Part 2, Audio Specifications, available from Philips System Standards and Licensing, Licensing Support, Building SFF-8, PO Box 80002, 5600 JB Eindhoven, The Netherlands

Manual part no: DOC135904 iss 2B2 Page 32 135904ma2b2.pdf file available from website

Contact dCS on + 44 1799 531 999	email to: more@dcsltd.co.uk
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