Noise Shaping; Table 3 - Noise Shaper Gain By Order And Sample Rate - DCS 900E User Manual

dCS 900E / 902E User Manual
dCS Ltd

Noise Shaping

The dCS 900 & 902 use noise shaping
curve
frequency response of errors (Q noise, or truncation errors) so that they fall as
much as possible in the less sensitive part of the spectrum. For all the major
sample rates (32 kS/s, 44.1 kS/s, 48 kS/s, 88.2 kS/s, 96 kS/s) the noise shapers
have been individually optimised. The 1
agree well with Wannamaker's published results
Noise Shaping adds more noise power, but because of the shaping it is
perceived as lower noise. There is a compromise to be drawn – as more
aggressive shaping is used, more noise is added, and less perceived
improvement occurs. In practice, things stop improving much above the 9
order. The increased real noise power can cause (small) clicks in editing, if this
is carried out after the shaping. For this reason, noise shaping should be used
as late as possible in the mastering process – we recommend recording at the
very highest possible sample rate and resolution, and only reducing either at the
latest possible minute.
If, however, you have to reduce word length, the perceived noise gain (taking
into account the ear's response) and the actual increase in noise (mainly out of
band) in given in the table below.
Sample
Rate
(kS/s)
32
44.1
48
88.2
96
176.4
192
The 3
order is very aggressive, and can give very large gains at the higher sample
rates. For example, 176.4kS/s or 192kS/s material truncated to 16 bits (so it
can be stored on a DA-88 or ADAT) loses nothing in the audio band in terms of
perceived noise, with 3
either see section
references below.
5
It actually uses an Error Shaping architecture, but the name is now being used for entirely other things and is
less well known, so we call it, erroneously, Noise Shaping
6
"Minimally Audible Noise Shaping", S.P.Lipshitz and R.A.Wannamaker, J AES vol 39 no 11, p836-852
7
"Psychacoustically Optimal Noise Shaping", R.A.Wannamaker, J AES vol 40 no 7/8, p611-620
Manual part no: DOC0029021E1
Contact on + 44 1799 531 999
dCS
(inside the UK replace + 44 with 0)
All manuals and user guides at all-guides.com
6
. It does not affect signal frequency or transient response, but shapes the
Perceived Actual
Gain, F Increase
weighted,
in Noise,
st
st
1 Order
1 Order
(dB)
(dB)
-3.3 1.9
-5.5 2.4
-6.2 2.5
-11.1 2.8
-11.8 2.9
-17.0 3.0
-17.7 3.0
Table 3 – Noise Shaper Gain by Order and Sample Rate
rd
order shaping tends to follow the E weighting curve, by chance. The 9
rd th
or 9 order shaping. For more information on this topic,
"Word Length Reduction"
Page 36
Manual for Software Versions 1.3x to 1.5x
5
that is optimised to the F weighting
st rd th
, 3 , and 9 shapes for 44.1 kS/s
7
.
Perceived Actual Perceived
Gain, F Increase Gain, F
weighted, weighted,
in Noise,
rd th
rd
3 Order 9
3 Order
(dB) (dB)
(dB)
-7.5 4.2 -8.1
-10.5 6.9 -17.9
-11.7 7.6 -21.0
-23.8 11.3 -42.2
-25.7 11.3 -45.3
-40.6 12.6 -63.0
-42.8 12.6 -65.9
on page 50 or read the
Document No: OS-MA-D0002-902.1E1
email to: more@dcsltd.co.uk
web site: www.dcsltd.co.uk
th
12 June 2000
th
Actual
Increase
in Noise,
th
Order
9 Order
(dB)
6.1
23.4
23.8
24.0
22.5
21.8
21.8
th