On 2006-10-29, Geoff wrote:
Jim Lesurf wrote:
In article , Mr.T
MrT@home wrote:
16 bits was an obvious choice because it's two bytes and provides a
sufficient degree of overkill. What you could also say is that not
for nothing was the early use and acceptance of 14 bit CD players,
when 16 bit converters were more difficult/expensive to make.

In fairness, I should point out, though, that the first generation
Philips '14 bit' chipsets for CD players actually used x4
oversampling. Thus - in principle at least - returned 16-bit
resolution.

Pray tell how oversampling increases resolution ? The reason for
oversampling was/is to make reconstruction filters easier to implemnt
without artifiacts of a steep slope. It's been a whil, have I forgotten ?

I have sometimes wondered about the Philips x4 upsampling DAC in early
CD players (I use "upsampling" here to distinguish from the use of
oversampling in the ADC case).

I assume (but have never looked for proof) that the conversion of a single
16-bit sample xx..xxYY (YY are the two LSBs) would be accomplished by
replacing the single 16-bit sample by four 14-bit samples as follows:

xx..xx00: xx..xx, xx..xx, xx..xx, xx..xx

xx..xx01: xx..xx, xx..xx, xx..xx, xx..xx+1

xx..xx10: xx..xx, xx..xx, xx..xx+1, xx..xx+1

xx..xx11: xx..xx, xx..xx+1, xx..xx+1, xx..xx+1

Or something similar. The DAC will effectively interpolate so the LSBs
are not lost. The noise floor will be right for 16 bits because of
the upsampling.

I wonder if the amplitudes of the preceding and succeding samples should
be taken into account to determine the right order of the +1s in the
interpolation? Probably not as I suspect the spectrum differences will
fall above the original Nyquist limit.

John
--
John Phillips