brb@philabs.UUCP (Brian Bertan) (04/16/84)
I can clearly see the advantages of the oversampling filters employed on
Philips type CD players. These are:
1) Reduced phase shift at high frequnecies
2) Use of 14 bits instead of 16 on D/A
3) Less sinc(f/f0) distortion
(Ref: Audio 4/84 and Philips Technical Journal 11/82)
I am curious if the CD manufacturers use oversampling filters when they
produce their discs. If they use an 11 pole elliptical anti-aliasing
filter the band limited analog signal being digitized will have
substantial phase shift. This defeats some of the advantages of an
oversampling reconstruction filter.
The CD manufacturers can obviously afford very sophisticated equipment.
Perhaps they four-fold (or two-fold) oversample the signal. Then they
have more bandwidth to attenuate the input signal. The data could then
be digitally filtered before going to the disc. This would require
digitizing at 176 KHz.
I'd really like to know how the signal proccessing is done.
Brian Bertan
Philips Labs
Briarcliff Manor, NY
{allegra | decvax | seismo}!philabs!brb (914) 945-6309
Disclaimer: This article does NOT represent the views of my employer --
Philips. I do not have anything to do with the CD program.