Meridian America Digital Audio Processor Meridian 518 - Manual (Page 53)

Appendix 4 –Resolution Enhancement 53
518 User Guide
such converters are used. Meridian has always used correct analogue de-
emphasis in its designs.
By wrapping 72-bit precision pre-emphasis and analogue de-emphasis
around a DAC, it effectively gains:
•
one bit noise reduction
•
two-bit increase in high-frequency resolution
•
more than ten-fold (20dB) reduction of converter noise.
These are substantial gains and are clearly audible on a good system.
On some material, using pre-emphasis will raise the overall signal level to
give 'clip' messages. It is still a great step forward to use pre-emphasis
with some overall gain reduction. In other words, if using pre-emphasis on
a piece of music causes clipping, try using Emphasis with the gain
reduced to –2 or –3dB. You are still winning on resolution with most DACs
up to –6dB.
10Hz 100Hz 1kHz 10kHz
-20
0
20
40
60
80
100
d
B
s
p
l
HP_Deem
HP
18
16
Figure 5. Showing the effect on audibility of the 518's High-
pass and Flat dithers. Also showing the noise reduction from
de-emphasis.
Dynamic-range optimisation with Noise-shaped
Dither
The section following page 37 describes some of the background to
noise-shaping.
Essentially noise-shaping works by an averaging method that is well
matched to human hearing. The noise-floor of the system is shaped by
moving energy from the mid-range – where listeners are most sensitive –
to high frequencies. A correctly designed noise-shaper allows the noise of
the channel to be made inaudible and allows resolution well below the
normal wordsize.
The diagram below shows how 518 can obtain inaudible noise and
effectively 20 bit resolution on a 16 bit CD!