Questions about equivalents of audio/video and digital/analog.

nospam@nospam.com (Don Pearce) writes:

> On Mon, 20 Aug 2007 11:31:16 -0400, Randy Yates <yates@ieee.org>
> wrote:
>
>>nospam@nospam.com (Don Pearce) 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.
>>
> No, it isn't. It misses the fact that sampled and digital are
> different things. Digits are numbers.

It isn't reaonable to you. Don't publish opinion as fact. 
   
>>I've also seen many contexts in which "digital" means "discrete-time,"
>>i.e., there is no amplitude quantization at all. Take for example any
>>of a number of books on the subject which have "digital signal
>>processing" in the title - they are referring to signals that have
>>been sampled in time, but not quantized (generally, although
>>quantization effects are also analyzed in several such texts).
>>
>
> Really? Can you point me at something that does DSP on signals that
> have been merely sampled in time? I've never come across any such
> thing.

You haven't looked very far. Here is an example (a power calculation):

  Px = \sum_{n=-\infty}^{+\infty} x^2[n],

where x[n] \in \R.

>>Do you have a reference for your definition?
>
> Logic will do. If you are doing digital signal processing, you are
> doing arithmetic on the numbers that come out of an AtoD converter.
> You can't do that with some voltage levels out of a quantizer.
>
> As for discrete time, that is simply sampled, like a class D
> amplifier, and nothing to do with digits. There is plenty of laziness
> in the use of nomenclature (as well as misuse by people who simply
> have no idea what they are talking about).

I won't argue that the current usage isn't good nomenclature, but that's
the way historically things have developed. 
-- 
%  Randy Yates                  % "Though you ride on the wheels of tomorrow,
%% Fuquay-Varina, NC            %  you still wander the fields of your
%%% 919-577-9882                %  sorrow."
%%%% <yates@ieee.org>           % '21st Century Man', *Time*, ELO
http://home.earthlink.net/~yatescr

Doug McDonald wrote:


>   ... It's very hard to STORE signals purely analog without
> moving parts. In fact, I had a hard time thinking of any such
> device that is or was purely analog. However, the old analog
> storage oscilloscopes would meet your criteria if you don't
> include electrons in a vacuum as moving parts. There the limit to the
> frequency response is the size of the focus spot .... i.e.
> the quality of the lenses! (Such device of course uses analog
> electron lenses). If you don't intend to store forever, there
> were things like analog mercury delay lines which stored signals
> as sound waves travelling through mercury.

I mentioned mercury delay lines in an earlier post that probably hadn't 
seen when you wrote that. There's another way that uses only common 
electrical components -- capacitors and inductors. Cascaded low-pass T 
(or pi) sections approximate a transmission line very well up to a 
frequency determined by the product of 1/LC, while the characteristic 
impedance is sqrt(L/C). Such "synthetic lines" were staples in telephone 
research labs. The Bell Labs exhibit at the 1939-40 Worlds Fair included 
such a line driven by a microphone into which a visitor could speak, 
feeding headphones (s)he wore while speaking. Most visitors were reduced 
to stammering by the delay, which I'm guessing was about two seconds; my 
memory on that point is hazy. I impressed my parents (much like Radium 
probably impressed his) by doggedly ignoring the feedback and speaking 
clearly and deliberately. The demonstrator, a Bell Labs researcher, 
asked us to wait while he fetched his boss to show me off. I do remember 
being told that delays up to ten seconds were feasible, but that long 
delays allowed the brain to more easily decouple speech and hearing, so 
they weren't used in the demo. Bossman showed us the closet where the 
delay line was stored. The parts were housed in two large relay racks.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Don Pearce wrote:

 > ... If you are doing digital signal processing, you are
> doing arithmetic on the numbers that come out of an AtoD converter.
> You can't do that with some voltage levels out of a quantizer.

Transversal and recursive filters and correlators have been built that 
operate on unquantized samples. Fourier transforms have been "computed" 
with lenses. Do you remember the early days of side-looking radar?

> As for discrete time, that is simply sampled, like a class D
> amplifier, and nothing to do with digits. There is plenty of laziness
> in the use of nomenclature (as well as misuse by people who simply
> have no idea what they are talking about).

Agreed. Sometimes I'm guilty of sloppiness. It's the flip side of 
explanatory excess.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

On Mon, 20 Aug 2007 04:47:00 -0800, glen herrmannsfeldt wrote:

>>> Well, some types of RAM bits are stored as analog voltages
>>> on a MOS gate capacitor. 
> (snip)
> 
>> These are/were the so-called  "bucket-brigade" nominally analog devices 
>> used as delay lines for audio effects such as phasers. Based on storing 
>> audio in a chain of capacitors (typ. NMOS, in VLSI chips). Sort of an 
>> analogue shift register. 
> (snip)
> 
> I believe there is a device more like an analog RAM used for
> sound recording in toys.  One can record up to about a
> minute of voice and replay it many times.

That's just normal (digital) RAM with an ADC and DAC.

"Randy Yates" <yates@ieee.org> wrote in message 
news:m31wdytcq2.fsf@ieee.org...
>>>I've never seen that definition, while I have seen the definition
>>>Floyd is proposing, and I think it is a reasonable one.
>>>
>> No, it isn't. It misses the fact that sampled and digital are
>> different things. Digits are numbers.
>
> It isn't reaonable to you. Don't publish opinion as fact.

OK, it's not reasonable to ME, either, if you're impressed
by taking a vote on this sort of thing.

The problem with the definition that you and Floyd seem to
want to use is that it leads to several problems in both
theory and practice, in addition to the fact that there are
numerous counter-examples one can point to.

"Reasonable" would seem (at least to me) to mean that you
can justify your definition *through reason*, which Don has
done.  Simply pointing to a published work, including a
standard, as a reference to support your definition is what's
called an "argument from authority," and it has exactly zero
weight in light of an opposing argument based on evidence
and logic.  However, if you like, I can also point to several
references which support the definition that Don and I (and
I believe others) are proposing.  You might claim the list to
be invalid, however, since it would contain works that I
myself wrote for publication.  Which is, of course, the whole
point - simply having your statements published does NOT
make them any more or less correct; the deciding factor is
whether or not they can be shown to be true through evidence
and logic.

Bob M.

>> Really? Can you point me at something that does DSP on signals that
>> have been merely sampled in time? I've never come across any such
>> thing.
>
> You haven't looked very far. Here is an example (a power calculation):

The question was flawed to being with, though - "DSP" stands
for "DIGITAL signal processing," which by definition could
not have been done on information that was simply "sampled
in time."  Such information would also have to be digitally encoded
in order to be subject to "DSP.:

> I won't argue that the current usage isn't good nomenclature, but that's
> the way historically things have developed.

A common misuse or misunderstanding does not become
less so merely because it IS common.

Bob M. 

On 8/20/07 8:41 AM, in article faccmf$sfh$1@usenet01.boi.hp.com, "Bob Myers"
<nospamplease@address.invalid> wrote:

> 
> "Floyd L. Davidson" <floyd@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.

No, it becomes a digitally encoded representative of a sample of an analog
voltage.  First the continuously variable analog signal is sampled,
becoming, for example PAM, which is still analog, which is then quantized
and may be fit to whatever digital or analog coding that is desired.  If
it's to a digital code, the signal is digital.  If to an analog code, the
signal is analog.  


> 
> 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.
> 
>>  QUANTIZATION:
>>      A process in which the continuous range of values
>>      of an analog signal is sampled and divided into
>>      nonoverlapping (but not necessarily equal)
>>      subranges, and *a* *discrete*, *unique* *value* *is*
>>      *assigned* to each subrange.
>> 
>>  http://ntia.its.bldrdoc.gov/fs-1037/
> 
> Exactly.  But mere quantization by itself does not
> suffice to render a signal "digitally encoded," no
> matter what a given government "expert" may claim.
> 
> Bob M.
> 
> 

Nobody wrote:

(snip)

>>I believe there is a device more like an analog RAM used for
>>sound recording in toys.  One can record up to about a
>>minute of voice and replay it many times.

> That's just normal (digital) RAM with an ADC and DAC.

No, they have ones that store analog voltages in memory
cells, instead of digitized bits.

See the ISD MICROTAD-16M for example:

http://www.datasheets.org.uk/search.php?q=ISD+MICROTAD-16M&sType=part&ExactDS=Starts

-- glen

Randy Yates wrote:

(snip)

> Let me back-pedal a little and say that, yeah, colloquially, digital
> is related to "digits." But the term "digital signal" as used in texts
> and industry does not hold to this colloquial usage. That is, a signal
> that is completely unquantized in amplitude and represented in base 10
> as an element of the real numbers could well be called a digital
> signal. The key property of such a signal is that it is *discrete-time*
> (i.e., sampled in time).

I would say that "digitized signal" also implies quantization.

There are analog sampled storage systems, such as:

http://www.datasheets.org.uk/search.php?q=ISD+MICROTAD-16M&sType=part&ExactDS=Starts

-- glen

Bob Myers wrote:

(snip)

> "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...;-)

How about, Analog implies "infinite" precision in the absence of
noise, including fundamental quantum noise.

Note, for example, that an analog current is quantized in units
of the charge on the electron.

-- glen

glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote in 
news:E6ednXh1JIkcRlTbnZ2dnUVZ_hynnZ2d@comcast.com:

> Bob Myers wrote:
> 
> (snip)
> 
>> "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...;-)
> 
> How about, Analog implies "infinite" precision in the absence of
> noise, including fundamental quantum noise.
> 
> Note, for example, that an analog current is quantized in units
> of the charge on the electron.
> 
> -- glen
> 

Doesn't "analog" also imply that x(t) exists for all t in range, and not 
just at nT for all n in range?  Or would people just call that "sampled"? 

-- 
Scott
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