Table 11 - Dither And Noise Shaping Noise Powers - DCS 900E User Manual

dCS 900E / 902E User Manual
dCS Ltd
11
DSD carries this further. The principle is the same, but with DSD, there is more noise than there is signal,
even at full scale. It is just that it is in a part of the spectrum the ear cannot hear.
12
16 bit Q noise is -98.1 dB relative to a full scale sine wave.
Manual part no: DOC0029021E1
Contact on + 44 1799 531 999
dCS
(inside the UK replace + 44 with 0)
Straight forward dither always adds noise – it can only produce signals with a
noise floor higher than Q noise on its own. However, the noise power added is
a few dBs for simple types. Noise shaping adds rather more noise, but it can be
made to add it in parts of the spectrum that the ear is less sensitive to, so the
perceived noise (F weighted noise) is lower – up to three bits lower. It results in
a signal that the ear hears as having a far lower noise floor than a 16 bit
truncated signal, rather than the "not much worse" of dither alone, even though
there is really more noise present
Truncation Type, with
44.1 kS/s data rate
16 bit truncation
16 bit truncation with
Top Hat dither
16 bit truncation with
Triangular dither
16 bit truncation with
Noise Shaped
Triangular dither
16 bit truncation with 3
order noise shaping and
no dither
16 bit truncation with 3
order noise shaping and
Noise Shaped
Triangular dither
16 bit truncation with 9
order noise shaping and
no dither
16 bit truncation with 9
order noise shaping and
Noise Shaped
Triangular dither
Table 11 – Dither and Noise Shaping Noise Powers
Noise shaping on its own is not perfect. It relies on a small amount of noise in
the input signal to generate the frequency shaped correction signal, and if there
is very low noise in the input signal, this mechanism can break down. With
ADCs, however, this situation does not arise, because of the analogue noise in
the ADC and the input signal.
Manual for Software Versions 1.3x to 1.5x
11
.
Noise,
unweighted,
F weighted,
rel 16 bit Q
rel 16 bit Q
12
noise
0 dB
3 dB
4.8 dB
4.8 dB
rd
6.9 dB
rd
11.0 dB
th
23.4 dB
th
28.2 dB
Page 51
th
12
Noise, Comments
noise
0 dB Unpleasant low
level effects
3 dB Okay – can show
noise modulation at
low signal levels
4.8 dB
modulation and
unpleasant effects
removed, but noise
floor is high
1.2 dB
modulation and
unpleasant effects
removed. Not much
perceived noise
-10.5 dB Okay with input
noise floors down to
-9.2 dB Unconditionally free
from truncation
effects with all
-17.9 dB Okay with input
noise floors down to
-16.7 dB Unconditionally free
from truncation
effects with all
Document No: OS-MA-D0002-902.1E1
email to: more@dcsltd.co.uk
web site: www.dcsltd.co.uk
June 2000
All noise
All noise
penalty
–102 dB
inputs
–120 dB
inputs