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dCS 904 User Manual Manual for Software Version 1.5x and 1.36
dCS Ltd June 2000
Manual part no: DOC135904 iss 2B2
Page 65
135904ma2b2.pdf file available from website
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dCS
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possibly get away with – the amount that simple 16 bit truncation (16 bit Q noise)
would give, if it were well behaved, which it is not.
xTruncation Type,
with 44.1 kS/s data
rate
Noise,
unweighted,
rel 16 bit Q
noise
11
Noise,
F weighted,
rel 16 bit Q
noise
Comments
16 bit truncation 0 dB 0 dB Unpleasant low
level effects
16 bit truncation with
Top Hat dither
3 dB 3 dB Okay – can show
noise modulation at
low signal levels
16 bit truncation with
Triangular dither
4.8 dB 4.8 dB All noise
modulation and
unpleasant effects
removed, but noise
floor is high
16 bit truncation with
Noise Shaped
Triangular dither
4,8 dB 1.2 dB All noise
modulation and
unpleasant effects
removed. Not much
perceived noise
penalty
16 bit truncation with 3
rd
order noise shaping and
no dither
6.9 dB -10.5 dB Okay with input
noise floors down to
–102 dB
16 bit truncation with 3
rd
order noise shaping and
Noise Shaped
Triangular dither
11.0 dB -9.2 dB Unconditionally free
from truncation
effects with all
inputs
16 bit truncation with 9
th
order noise shaping and
no dither
23.4 dB -17.9 dB Okay with input
noise floors down to
–120 dB
16 bit truncation with 9
th
order noise shaping and
Noise Shaped
Triangular dither
28.2 dB -16.7 dB Unconditionally free
from truncation
effects with all
inputs
Table 12 – Dither and Noise Shaping Noise Powers
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
12
.
11
16 bit Q noise is -98.1 dB relative to a full scale sine wave.
12
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.