In article , Arny
Krueger
wrote:
I found the spec sheet for the TDA1540 and SAA 7030 online, and can
confirm that noise shaping is done in the SAA 7030.
The TDA 1540 spec sheet was found at the Signetics web site.
BTW the speced dynamic range of the TDA 1540 is 85 dB.
Not read the data sheets. However I've now had a chance to re-read the
special issue of Philips Tech Rev that includes
Digital-to-analog conversion in playing a Compact Disc.
Goedhart, et al.
Philips Tech Rev V40(6) 1982 pages 174-9
This paper outlines how the SAA7030 and TDA1540 operate as part of the
conversion system.
This confirms the noise shaping, essentially by the method of taking the
LSB portion of the 28 bit accumulator and employing it as a carry forwards
to combine with the next filter-computed oversample.
Although the dynamic range is around 85dB this is essentially for the x4
bandwidth, and the paper explains that the result should end up being more
like 97dB if the devices operate as intended.
Two reasons for this.
1) Even with a 'white' quantisation noise spectrum the final bandwidth only
covers a quarter of the oversampled rate bandwidth, so this would give a
6dB improvement.
2) The noise shaping actually generates a noise spectrum which rises with
frequency, thus the 85dB noise is predominantly above 22kHz. This improves
the result according to their analysis by another 7dB or so over what you'd
get for 'white' noise.
The results are broadly in line with the use of noise shaping in other,
more modern, oversampling systems that use lower bit-depths than the input
data.
Given that this was the first system Philips used, it still looks
remarkably 'fresh' in concept. Hardly surprising that some marketing types
and journalists have had to use the term 'upsampled' more recently to try
and pretend they have come up with a new idea, when this may not always be
so. :-)
Slainte,
Jim
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