What Does It Look Like; Figure 28 - Noise Shaping And Dither Spectra - DCS 900E User Manual

dCS 900E / 902E User Manual
dCS Ltd
There is another option not supported by the dCS 900 & 902 – generate the dither
independently of the signal and frequency shape it prior to addition, but do not
add it in an error shaping loop. This seems to dCS to combine the worst of all
worlds – the high noise floor in the 0-6 kHz area of straight dither, and the high
total noise of noise shaping. However, some people use it.

What does it look like?

Figure 28 gives the spectra of 16 bit truncated 44.1 kS/s signals with a –90dB
sine present, for two dither only signals (Top Hat, Noise Shaped Triangular), and
with a 10
The equivalent simply truncated spectrum is shown in Figure 29, separately
because it is so revolting. In it, we can see that at the signal level shown
(-90 dB) error power from the quantising/truncation is beginning to pile into the
fundamental, which is showing an amplitude error of +1.3 dB, as well as all the
unwanted harmonics.
although the sign of the error could be either way.
We see that the noise shaping approach maintains low noise in the critical audio
mid band.
-60
-80
-100
-120
-140
-160
0 2 4
13
for comparison with the table, 10
Manual part no: DOC0029021E1
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-
th 13
order noise shaped
This would show up on a conventional linearity plot,
Noise Shaper and Dither Only Comparison
dCS 972 SW v1.54
16 bit truncation, Noise Shaped Triangular dither
16 bit truncation, Top Hat dither
16 bit truncation, high order noise shaping only
44.1 kS/s sampling, 1024 point FFTs, H6 window, -90 dB 1.44 kHz input
6 8 10
Frequency (kHz)
Figure 28 – Noise Shaping and Dither Spectra
th th
and 9 order noise shaping are very similar.
Page 52
Manual for Software Versions 1.3x to 1.5x
signal, generated and processed by a dCS 972.
12 14 16 18
Document No: OS-MA-D0002-902.1E1
email to: more@dcsltd.co.uk
web site: www.dcsltd.co.uk
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12 June 2000
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