Meridian America Digital Audio Processor Meridian 518 - Manual (Page 47)

Appendix 2 – Hints on Mastering 47
518 User Guide
dynamic range is extended. Implicit in this theory is the fact that the digital
channel has near-infinite differential linearity, i.e. each bit has a magnitude
precisely twice or half the magnitude of the next.
When this signal is applied to a D/A converter some problems may arise.
First the D/A process may be associated with an oversampling digital
filter. Commonly these parts take no precautions with regard to dither and
introduce a quantisation noise-floor themselves at the approximate level
of the LSB in the filter, thereby obliterating lower-level information in the
signal. Secondly the D/A converter will not have perfect differential
linearity – there is no longer any reason why successive bits will maintain
a precise 2:1 ratio. The effect of this is also equivalent to quantisation at
the linearity level of the converter.
In summary therefore, the wide subjective dynamic range inherent in the
recording cannot be reproduced unless the replay D/A system has both a
word-size (in terms of associated oversampling filters) and a differential
linearity equivalent to the original material, which in this example was 20
bit. The result would be further improved by the correct use of dither and
noise-shaping in the digital filter.
That a subjective channel dynamic range of approaching 20 bit can be
conveyed on a 16 bit channel is quite remarkable. On reflection, it should
not be surprising that to realise this benefit, both the A/D and D/A sub-
systems must have the required 20-bit precision.