On Mon, 13 Nov 2017 09:59:52 +0000, Jim Lesurf wrote:

In article , Woody
wrote:


Interesting observation.

For some reason I always thought my first 14-bit Philips (CD104?)
sounded better than anything I had later, and that the one that I
bought to replace it some years later (16-bit parallel) also sounded
better. That machine now sits with a very elderly lady we know and I
will reclaim it when she passes. Comparison with my present Marantz
CD5400SE will be interesting.

The first player I had was the first gen Marantz using the 14-bit x4
Philips chipset. Happy with it for about a decade. Although I did add
some 'Toko' analogue low pass filters that rolled off at about 19 kHz as
that seemed to make the results sound nicer to my ears. Possibly because
it cut down the signal levels slightly going into the amp.


You seem to have forgotten that one of the benefits of 4x oversampling
eliminated the need for a brick wall anti-aliasing filter to allow a
filter with a much gentler roll off slope to be used which produced much
less in-band ripples in its response curve.

It's just possible that your Toko analogue filter may have been
filtering off low level supersonic products in the 20 to 60KHz range that
were upsetting the amplifier's stability, perhaps creating
intermodulation products of its own, leading to a slightly dirtier sound
as a result. The other thing about Philips's rather neat use of 4 times
oversampling with 14 bit DACs to achieve the same accuracy and dynamic
range of a perfect 16 bit DAC was the improved accuracy of monotonicity
over that of the typical consumer grade 16 bit DACs of the day. It really
was a very clever move on the part of Philips at the time.

Nowadays, this oversampling principal has been taken to its ultimate
conclusion with very high speed single bit DACs that oversample with a
factor of 65536 (or is it 32768? - 1440MHz is the sampling frequency ISTR)
times the 44.1KHz sampling rate which corresponds to a sampling frequency
of some 2.88GHz. Whatever it is (32768 or 65536) it's an extremely high
sampling rate whichever way you look at it - makes a 44.1KHz sampling
rate look positively pedestrian indeed.

The oversampling frequencies might seem rather extreme but the big
payback is that a single bit DAC doesn't need the extreme accuracies
required by the last two or three MSBs used by 16 and 14 bit parallel
converters of old. Indeed, not even the accuracy of the next to LSB of
such converters, just a reasonable accuracy to avoid clipping in the
following analogue stages of the DAC which error can be compensated for
with a simple 'volume control' trim pot if required. Monotonicity
guaranteed, absolutely! :-)


--
Johnny B Good