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DCS dCS 974, Digital to Digital Converter Dither, Noise, Power, Power, Noise, Added, (0-Fs/2), Perceived, Dither Type, Added Noise, (unweighted), dCS 974 Performance Curves

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dCS 974 User Manual	Manual for Software Version 1.0x
dCS Ltd	May 2001

Dither

The dCS 974 uses relatively unusual dither generators to achieve the very good statistics necessary for audio purposes. Many dither generators use PRBS generators (Pseudo Random Binary Shift register generators). These are well known, well documented, and very predictable – but unfortunately their statistics are not that great. The problem shows up as a spectrum that is not flat, and histograms (PDFs, Probability Density Functions) that diverge from the ideal quite significantly.

Adding dither adds noise. Top hat dither uses one generator per channel to add ±0.5 lsbs p-p of rectangularly distributed dither, and triangular dither uses two generators per channel to add ±1 lsbs p-p of triangularly distributed dither. This is on top of the Q/√12 rms dither from word length reduction in the first place (where Q is the size of the output word lsb). The noise shaped triangular setting uses one generator to add ±1 lsbs p-p of triangularly distributed dither that is frequency shaped, and so has low perceived (weighted) noise power. This last is a significant test of generator performance – the dCS 974 performs very well. Performance curves for all these settings, including PDFs of the added dither, are given in the dCS 974 Performance Curves, page 94.

The noise added by the dither settings is summarised below:

Dither Type	Noise	Added Noise	Perceived
	Power	Power	Noise
	(0-Fs/2)	(unweighted)	Added
			(F weighted)
No dither	Q/√12	0 dB	0 dB
(straight truncation)
Top Hat dither	Q/√6	3 dB	3 dB
Triangular dither	Q/√4	4.8 dB	4.8 dB
Noise Shaped Triangular	Q/√4	4.8 dB	1.2 dB
dither

Table 10 – Noise Added by Dither Types

If dither is used, it is shaped (made less audible) by noise shaping. This applies as much to noise shaped triangular as the others.

Manual part no: DOC1241121A1

Page 85

Document No: OS-MA-A0124-112.1A1

Contact dCS on + 44 1799 531 999	email to: more@dcsltd.co.uk
(inside the UK replace + 44 with 0)	web site: www.dcsltd.co.uk

Contents

© 2001 dCS Ltd dCS Ltd PRODUCT OVERVIEW Monitoring Test Generator Ease of Use About this Manual About Sample Rates CONTENTS The Hardware – Controls and Connectors Page Page STEP-BY-STEP GUIDE Preliminaries Step 1 – Selecting an Input Connecting to a Dual AES Source Connecting to a Quad AES source Connecting to a DSD SDIF-2source WCLK IN Connecting to a DSD Quad source Step 2 – Setting the Sync Source Syncing to an AES/EBU Reference AES Ref Loop Step 3 - Setting a Conversion proceed to Setting the Output Mode Setting the Output Sample Rate Setting the Output mode Step 4 – Connecting the Outputs Step 5 – Reducing the Output Wordlength Proceed to Other Settings Other Settings Sample Rate Conversion / Format Conversion Submenu TYPICAL APPLICATIONS Converting a 24/96 recording to CD format Demultiplexing a 24/96 Dual AES recording (Bit for Bit) Upsampling a CD General Sample Rate Conversion and Distribution PCM to DSD Using a Master Clock Converting Quad AES to CD Format Multi-channelSample Rate Conversion – bit aligned sources Multi-channelSample Rate Conversion – Using a Master Clock Multi-channelSample Rate Conversion – with more alignment tolerance Multi-channelSample Rate Conversion – with multiple sample rates out Page THE SOFTWARE – MENU AND SETUPS Page Navigating through the Menu – what the On-Screensymbols mean Page Top Menu Error Monitoring Test Info Bit Activity Monitors NOT Level Meters Display Sample Rate Conversion / Format Conversion Submenu Multiple Channel Sync Multiple Channel Sync’ing Single Master Slave Input Sample Rate Output Sample Rate 1 pass INPUT SAMPLE RATE (kS/s) OUTPUT SAMPLE RATE (kS/s) 2 Pass Output Mode AES Clk Output SDIF Clk Output dCS 974 Performance Curves Out Number of Filters Available Output Word Length Noise Shaping AES Message Edit SPDIF Message Edit Gain/Balance and Maximise not Swap Channels L/R Flip Phase Detect Silence De/Pre-Emphasis Display Customise Page Error Monitor Submenu Test Submenu Generator Amplitude Adjustment Generator Frequency Adjustment Self Test Info Submenu Bit Activity Monitor Submenu Level Meters Submenu Meter Type (Bar or Numerical) Decay Time Set Using the dCS 974 to monitor a track Watch Out for this One Display Submenu Setups and Locking the Front Panel Demo “First choose a name!” AES2 DSD DSDQ Fixed Setups AES1 Au>24 DA Au>CD N9 F2 QA Au>CD N9 F2 DSD2>CD N9 F2 Locking Out Changes, and Unlocking Again Error Monitor Bit Activity Monitor Level Meter Page THE HARDWARE – CONTROLS AND CONNECTORS Rear Panel Signal Outputs AES/EBU Digital Outputs 3 pin XLR Male (4 off – AES 1, AES 2, AES 3, AES 4) AES 2, AES AES/EBU Clock Output3 pin XLR Male (1 off – AES CLK OUT) Front Panel LED indicators Noise shaping L/R flip Gain Balance Digital Data Formats Supported DSD E2 spec E3 spec DSD Data Formats PCM Input and/or Output Performance Spurs Noise Group Delay Group Delay (∝s) Sample Period (∝s) Conversion Clocking Sample Alignment SDIF WCLK IN Page Page Multiple Channel Sync’ing Page Multiple Channel Multiple Sample Rate Synchronising Noise Shaping Dither Digital Interface Specifications SPDIF (optical) Message Handling SPDIF Message Handling SDIF-2Message Handling DESCRIPTION Definition Default Message Power Consumption Size, Weight and Operating Conditions Page dCS 974 PERFORMANCE CURVES Page Page Page Page Page Page Page Page Page GENERAL TECHNICAL INFORMATION Word Length Reduction lower Truncation Type, with Noise 44.1 kS/s data rate unweighted What does it look like Page When is Dither Needed Page USING YOUR dCS 974 FOR THE FIRST TIME What’s in the Box Supply Voltage Setting Getting Started Page Installing the Unit in a Rack Page OPTIONS Locking to Video Sample Rates Mains Supply Voltage Ordering Options for a New Unit Having Your Options Changed Page MAINTENANCE AND SUPPORT Hardware Software Warranty Update or Calibration Safety and Electrical Safety TROUBLESHOOTING FAQs Page “Invalid Fs Out for Fs In” message The Customise Display menu will not allow another option to be set If You Need More Help Other Information INDEXES AND SOFTWARE VERSION NUMBERS Definitions of Units Tables Figures Keywords and Phrases Page Page Page Page Owner Registration Transfer