On 20 Aug., 10:04, (Don Pearce) wrote:
On Mon, 20 Aug 2007 03:51:54 -0400, Jerry Avins wrote:
Don Pearce wrote:
On Sun, 19 Aug 2007 23:26:16 -0700, (Dave Platt)
wrote:
"Digital" and "subject to aliasing" are two different things.
As I believe the term "digital" is usually meant, it implies a
two-state (on/off) storage representation. It's not just that the
signal amplitude is quantized, but that the quantization uses a
power-of-two representation and storage system of some sort.
My reading of the possible systems goes like this.
analogue - a continuous representation of the original signal
sampled - a representation of the signal at discrete time points
quantized - a sampled signal, but with the possible levels constrained
to a limited set of values
digital - a quantized signal, with the individual levels represented
by numbers
Aliasing is going to happen as soon as you move beyond the first line
of that list.
I like your categories. It is possible in concept to have a signal that
is quantized in magnitude and continuous in time, but (unless we resort
to counting electrons) I don't think it's possible in practice.
Yes, I was thinking about that possibility while I was typing, but
since I've never come across such a system I decided it would
complicate things unnecessarily to include it.
Yannis Tsividis once asked in comp.dsp what signal processing
practitioners thought of his continuous-time signal processing
(filtering) scheme. As I remember, it didn't go down well with the
crowd. After reading a paper from him explaining the concept I thought
that the scheme had at least educational merit. There are some
references on his webpage:
http://www.ee.columbia.edu/fac-bios/...s/faculty.html
Regards,
Andor