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Author: Jerry AvinsJerry Avins Date: Aug 20, 2007 08:22
glen herrmannsfeldt wrote:
> Dave Platt wrote:
>
> (snip)
>
>> 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.
>
> It means discrete states, but the base does not have to be two.
>
> Many of the early computers were decimal based, and not
> necessarily BCD.
>
> The Fortran standard still allows for any base greater
> than one to be used for representing values.
Glenn,
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Author: Bob MyersBob Myers Date: Aug 20, 2007 08:26
> On Aug 19, 8:34 pm, "Bob Myers" wrote:
>
>> Sampled analog systems are certainly
>> not very common today (unless you count certain forms of
>> modulation as "sampling," and in fact there are some very close
>> parallels there), but the theory remains the same no matter which
>> form of encoding is used. In any event, you must sample the
>> original signal at a rate equal to at least twice its bandwidth
>> (actually,
>> very slightly higher, to avoid a particular degenerate case which
>> could occur at EXACTLY 2X the bandwidth) in order to preserve
>> the information in the original and avoid "aliasing."
>
> Is the CCD [Charge Coupled Device] a "sampled...
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Author: Bob MyersBob Myers Date: Aug 20, 2007 08:31
"Dave Platt" radagast.org> wrote in message
news:8ponp4-gfd.ln1@radagast.org...>>Come on, Dave, a CCD is a digital device, subject to aliasing. The
>>charges represent the signal at a particular instant of its average over
>>a particular interval. (My CCD digital camera can take time exposures.)
>>A CCD's content may not be quantized in amount, but it is quantized in
>>time. In a camera, where the charges pertain to individual pixels, the
>>result is also quantized in space.
>
> "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.
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Author: Randy YatesRandy Yates Date: Aug 20, 2007 08:31
> [...]
> On Mon, 20 Aug 2007 05:46:19 -0800, floyd@ apaflo.com (Floyd L.
> Davidson) wrote:
> >>A "quantized analogue signal" is digital by definition.
>>
>
> No, you haven't. You merely have a signal at a set of discrete levels.
> You need an analogue to digital converter to take each of those
> quantized levels and convert it into a digital word (of 1s and 0s).
>
> Digital means "represented by digits", not "in discrete voltage
> steps".
I've never seen that definition, while I have seen the definition
Floyd is proposing, and I think it is a reasonable one.
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Author: Bob MyersBob Myers Date: Aug 20, 2007 08:32
"Don Pearce" nospam.com> wrote in message
news:46cd3d5b.233043828@news.plus.net...> analogue - a continuous representation of the original signal
A CCD is an example of a device which stores information
in an analog manner, but non-continuously.
Bob M.
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Author: Bob MyersBob Myers Date: Aug 20, 2007 08:36
"Floyd L. Davidson" apaflo.com> wrote in message
news:87zm0mjrfy.fld@apaflo.com...>>digital - a quantized signal, with the individual levels represented
>>by numbers
>
> It makes no difference how the levels are represented.
Sure it does. If the levels of the original signal (or rather,
whatever parameter of the original information is being
recorded/stored/process are represented by analogous
levels of some other parameter (e.g., sound represented
by voltage), then the system is "analog." It is certainly
possible to conceive of a quantized analog system, although
such things are rarely if ever seen in practice.
"Analog" also does not imply "infinite" precision or
adjustability, since, as is the case in ALL systems, the achievable
precision (and thus the information capacity) is ultimately limited
by noise. See the Gospel According to St. Shannon for
further details...;-)
Bob M.
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Author: Bob MyersBob Myers Date: Aug 20, 2007 08:41
"Floyd L. Davidson" apaflo.com> wrote in message
news:87r6lyjp3o.fld@apaflo.com...
> A "quantized analogue signal" is digital by definition.
No, Don had it right. A quantized analog signal
remains analog as long as the relative values of the
quantization levels, one to the other have significance;
they thus can carry information, which is the fundamental
goal of any such system.
Now, we could certainly assign values to those levels
which (for instance) are NOT in order from "top to
bottom" (or whichever direction you choose to use),
which might be done to distribute the susceptibility of
any given "bit" in said value to noise evenly. In this
case, the levels MUST be interpreted as the intended
numeric values in order to recover the original
information, and hence this would be a "digital"
encoding system.
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Author: Jerry AvinsJerry Avins Date: Aug 20, 2007 08:42
Floyd L. Davidson wrote:
>> On Mon, 20 Aug 2007 04:57:03 -0800, floyd@ apaflo.com (Floyd L.
>> Davidson) wrote:
>> >>> Jerry Avins ieee.org> wrote:>>>> 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.
>>> If you quantize the magnitude, it is digital. That is
>>> by definition.
>> No it isn't. It isn't digital until you assign numerical values to
>> those quantized levels. Until then it is simply a quantized analogue
>> signal.
>
> If you quantize it, you *have* assigned a value to it,
> and that value is not from a continuous set, but from a
> discrete finite set, and therefore it is digital.
> ...
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Author: Randy YatesRandy Yates Date: Aug 20, 2007 08:46
Randy Yates ieee.org> writes:
>> [...]
>> On Mon, 20 Aug 2007 05:46:19 -0800, floyd@ apaflo.com (Floyd L.
>> Davidson) wrote:
>> >>>A "quantized analogue signal" is digital by definition.
>>>
>>
>> No, you haven't. You merely have a signal at a set of discrete levels.
>> You need an analogue to digital converter to take each of those
>> quantized levels and convert it into a digital word (of 1s and 0s).
>>
>> Digital means "represented by digits", not "in discrete voltage
>> steps".
>
> I've never seen that definition, while I have seen the definition
> Floyd is proposing, and I think it is a reasonable one.
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