User Guide

dCS Purcell User Manual Manual for Software Issue 2.2x
dCS Ltd September 2004
Manual filename: Purcell Manual v2.2x.doc Page 24 email: [e-mail]
English version web-site: www.dcsltd.co.uk
N.Shape
N.ShapeN.Shape
N.Shape – Noise Shaping
The unit can be used to noise shape signals where the wordlength is being
truncated (set to less than 24 bits).
do this: Open the Menu and step through until the display shows N.Shape.
do this: Press the
Select button once.
Assuming for this example that Noise Shaping is currently switched off, the
display will change to Off.
do this: Press the
Select button slowly five times. The display will show in turn: 1st, 3rd,
9th, Auto and finally Off.
do this: Choose the setting you want and wait for the Menu to time-out.
The NS indicator in the status indicator block lights when Noise Shaping is set
to 1st, 3rd or 9th. It also lights when Noise Shaping is set to Auto with Out
Word set to less than 24 bits.
In Auto mode, Noise Shaping is applied as follows:
Out Word
Out WordOut Word
Out Word N.Shape
N.ShapeN.Shape
N.Shape
23 – 24 bits
Off
21 – 22 bits
1st
17 – 20 bits
3rd
16 bits
9th
Table 2 – Auto Noise Shaping settings
It is generally best to leave Noise Shaping set to Auto as this will always give
a sensible setting. Otherwise, consult Table 1 for the appropriate setting.
For more information about Noise Shaping, please see “Wordlength Reduction”
on page 52. Note that for 176.4 or 192kS/s output sample rates, the Out Word
setting cannot be changed from 24 bits, so Noise Shaping is disabled.
Dither
DitherDither
Dither
The unit can add Dither to the signal if necessary – and has several dither
options. We recommend you only add Dither if it is really necessary – it
inevitably degrades the noise performance of the system.
do this: Open the Menu and step through until the display shows Dither.
Assuming for this example that Dither is currently switched off, the display will
change to Off.
do this: Press the
Select button slowly four times.
The display will show in turn the dither types available: Top Hat, Triangle, N.Tri
(Noise Shaped Triangle) and finally Off.
do this: If the DAC you are using will accept 24 bit input data, set Dither to Off.
Otherwise, consult Table 1 for the appropriate setting. Choose the setting you
want and wait for the Menu to time-out.
For more information about Dither, please see “Wordlength Reduction” on page
52. Note that for 176.4 or 192kS/s output sample rates, this setting cannot be
changed - Off is selected automatically.