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Sci.Electronics.Basics -> Questions about equivalents of audio/video and digital/analog.
There are 304 messages in this thread.
You are currently looking at messages 280 to 300.
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Author: Floyd L. DavidsonDate: 18:16 27-08-07
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Jim Kelley <jwkelley@uci.edu> wrote:
>Floyd L. Davidson wrote:
>> You are implying that any dictionary definition (hence
>> not your unique Alice in Wonderland definition) is
>> correct in any context.
>
>I'm not implying that at all. I'm simply saying that
>the terms and definitions I used are correct in the
>context in which I used them.
The were easily demonstrated as *not* correct in the
context used, and your whole discussion since has been
to argue the implication as stated above.
Do you read what you write?
Lets review it:
Here are some valid standard defintions:
"quantize - to subdivide into small but measurable increments."
(Merriam Webster's Collegiate Dictionary, Tenth Edition)
Your source is for common English, it is not defining
the Terms of Art used in technical discussions. This
*is* a discussion about those terms of art, not about
common English word usages. To whatever degree your
cited definition differs from the standard definitions
I've cited, you are wrong because of the context.
Here is the standardized definition for "quantization"
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.
And you looked at a invalid definition for this context and
stated:
Note that in the definition, there appears no
mention of assigning a value. Assigning a value
would then be considered a part of a separate and
distinct process of converting to digital form, as
in
Obviously the Term of Art used in technical discussion
does indeed mean there *must* be a value assigned. In
fact it makes no sense at all unless that step is
included.
Then you go on to produce other, equally invalid in this
context, definitions for other terms of art:
"digital - of, or relating to data in the form of
numerical digits",
and as opposed to
"analog - of, relating to, or being a mechanism
in which data is represented by
continuously variable physical
quantities."
The first definition states that the form must be "of
numerical digits", and that is simply unnecessary. It
must be assigned a "value". The value can be numerical
digits, but it can be otherwise too. The point is that
it must be from a finite set of discrete values. (I
used the example of flags, where the value might be a
square flag, a round flag, or a triangular flag. No
numerical digits at all.)
As you can see, knowing how to use a dictionary is
vitally important...
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>;
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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Author: Jim KelleyDate: 18:23 27-08-07
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Floyd L. Davidson wrote:
> Jim Kelley <jwkelley@uci.edu> wrote:
>
>>Floyd L. Davidson wrote:
>>
>>>You are implying that any dictionary definition (hence
>>>not your unique Alice in Wonderland definition) is
>>>correct in any context.
>>
>>I'm not implying that at all. I'm simply saying that
>>the terms and definitions I used are correct in the
>>context in which I used them.
>
>
> The were easily demonstrated as *not* correct in the
> context used, and your whole discussion since has been
> to argue the implication as stated above.
>
> Do you read what you write?
>
> Lets review it:
>
> Here are some valid standard defintions:
>
> "quantize - to subdivide into small but measurable increments."
> (Merriam Webster's Collegiate Dictionary, Tenth Edition)
>
> Your source is for common English, it is not defining
> the Terms of Art used in technical discussions.
It perfectly defines the term as I use it.
> This
> *is* a discussion about those terms of art, not about
> common English word usages. To whatever degree your
> cited definition differs from the standard definitions
> I've cited, you are wrong because of the context.
I don't use the term the way your reference defines it.
> Here is the standardized definition for "quantization"
>
> 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.
>
> And you looked at a invalid definition for this context and
> stated:
>
> Note that in the definition, there appears no
> mention of assigning a value. Assigning a value
> would then be considered a part of a separate and
> distinct process of converting to digital form, as
> in
>
> Obviously the Term of Art used in technical discussion
> does indeed mean there *must* be a value assigned. In
> fact it makes no sense at all unless that step is
> included.
It seems there are a great many things that don't make sense to you.
If a "term of art" were to be defined in such a way that it
contradicts the definition for the exact same term as it is published
in Websters dictionary, I would be inclined to disregard it.
> Then you go on to produce other, equally invalid in this
> context, definitions for other terms of art:
>
> "digital - of, or relating to data in the form of
> numerical digits",
>
> and as opposed to
>
> "analog - of, relating to, or being a mechanism
> in which data is represented by
> continuously variable physical
> quantities."
>
> The first definition states that the form must be "of
> numerical digits", and that is simply unnecessary. It
> must be assigned a "value". The value can be numerical
> digits, but it can be otherwise too. The point is that
> it must be from a finite set of discrete values. (I
> used the example of flags, where the value might be a
> square flag, a round flag, or a triangular flag. No
> numerical digits at all.)
> As you can see, knowing how to use a dictionary is
> vitally important...
Perhaps almost as important as realizing at which side of the analog
to digital convertor you're looking.
jk
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Author: Dan CobyDate: 18:45 27-08-07
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Will you two just get a room. Please.
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Author: Floyd L. DavidsonDate: 22:35 27-08-07
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Jim Kelley <jwkelley@uci.edu> wrote:
>Floyd L. Davidson wrote:
>> Jim Kelley <jwkelley@uci.edu> wrote:
>>
>>>Floyd L. Davidson wrote:
>>>
>>>>You are implying that any dictionary definition (hence
>>>>not your unique Alice in Wonderland definition) is
>>>>correct in any context.
>>>
>>>I'm not implying that at all. I'm simply saying that
>>>the terms and definitions I used are correct in the
>>>context in which I used them.
>> The were easily demonstrated as *not* correct in the
>> context used, and your whole discussion since has been
>> to argue the implication as stated above.
>> Do you read what you write?
>> Lets review it:
>> Here are some valid standard defintions:
>> "quantize - to subdivide into small but
>> measurable increments."
>> (Merriam Webster's Collegiate Dictionary, Tenth Edition)
>> Your source is for common English, it is not defining
>> the Terms of Art used in technical discussions.
>
>It perfectly defines the term as I use it.
Yes. And in a technical discussion, you are off in Alice's
Wonderland.
>> This
>> *is* a discussion about those terms of art, not about
>> common English word usages. To whatever degree your
>> cited definition differs from the standard definitions
>> I've cited, you are wrong because of the context.
>
>I don't use the term the way your reference defines it.
But nobody else, unless they are also in Wonderland,
knows what you mean if you don't use standard definitions.
And in a *technical* discussion, that means the technical
term of art, not the common English term.
...
>> Obviously the Term of Art used in technical discussion
>> does indeed mean there *must* be a value assigned. In
>> fact it makes no sense at all unless that step is
>> included.
>
>It seems there are a great many things that don't make
>sense to you.
Why people want to make absurd claims about terminology
is one of them. Maybe you can explain that...
>If a "term of art" were to be defined in
>such a way that it contradicts the definition for the
>exact same term as it is published in Websters
>dictionary, I would be inclined to disregard it.
It isn't a contradiction. The term of art is usually a
stricter definition. It is certainly going to be more
rigorous.
Regardless, to ignore it is abject foolishness. Can you
imagine a lawyer in court ignoring all of the term of
art definitions in favor of the standard common English
dictionary definitions? The other side would be
ecstatic... and the judge would probably throw the
lawyer out the door!
If you don't want to use the technical terminology, why
not just step out the door and avoid all technical
discussions? You won't make sense, it it does become
annoying.
>> As you can see, knowing how to use a dictionary is
>> vitally important...
>
>Perhaps almost as important as realizing at which side
>of the analog to digital convertor you're looking.
Exactly. Now, if you don't want to use terms in a what
that will be understood, how can you even tell which
side is which?
You'll end up making grossly trivial errors the way
Jerry Arvins and a couple of others here do...
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>;
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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Author: Floyd L. DavidsonDate: 22:35 27-08-07
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On Aug 19, 8:00 pm, Radium <gluceg...@gmail.com> wrote:
> On Aug 19, 7:48 pm, Stanislaw Flatto <comp...@brownbear.com.au>
wrote:
>
> > Audio IS mechanical so something has to move.
>
> Then how is it possible for a digital audio device [like an iPod]
to
> play audio back w/out moving a disc or tape? There is a digital
chip
> storing info and playback does not require moving anything. Just
how
> is this possible? If it works in digital, why can't it work in
analog?
What is 'moving' isn't the tape, it's the address counter in the
playback RAM. If you stop the address counter you will get exactly the
same result as if you stopped the tape or the turntable -- nothing.
The address counter is most certainly in motion - if you change the
rate it counts, the pitch of the output changes. It just isn't
directly visible without a logic analyzer. If you make it count
improperly, it can mimic the stylus skipping on a record. Just as you
can run out of tape, you can run out of addresses.
The way a tape recorder works is to constantly replace the magnetic
'core' of the transformer (the head) by dragging it away as tape.
You know too many buzzwords but not what they mean or imply. Go read -
a LOT.
GG
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Author: Jerry AvinsDate: 00:21 28-08-07
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Floyd L. Davidson wrote:
> Jerry Avins <jya@ieee.org> wrote:
>> Floyd maintains that any signal whose values are
>> restricted to a finite set -- IOW, "quantized" -- is
>> digital. I cited a two-level analog signal and I can
>> demonstrate a digital signal with a relatively large
>> continuous range of values. His definitions are simply
>> too restrictive to accommodate those, and he seems to be
>> having a fit.
>
> I'll admit to a really great fit of laughter at that one!
>
> You are so thoroughly confused that it is hilarious.
>
> The recognized standard definitions say that a quantized
> signal is digital. You can indeed have a two-level
> analog signal, but the fact is that the *possible*
> values are infinite (all values between your two listed
> ones, for example). You cannot possibly have a digital
> signal with a continuous range of values (large or
> small, relative or otherwise).
>
> I've cited multiple credible sources that agree with
> what I say. You can't cite even one. There are none.
There are only two possible values for the output of a hard limiter.
Make something of it. OTOH, bu using CMOS logic and varying the power
supply voltage randomly between the limits of 3 volts and 18 volts, I
can hive a digital signal an infinite number of values.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
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Author: Floyd L. DavidsonDate: 00:52 28-08-07
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Jerry Avins <jya@ieee.org> wrote:
>Floyd L. Davidson wrote:
>> Jerry Avins <jya@ieee.org> wrote:
>>> Floyd maintains that any signal whose values are
>>> restricted to a finite set -- IOW, "quantized" -- is
>>> digital. I cited a two-level analog signal and I can
>>> demonstrate a digital signal with a relatively large
>>> continuous range of values. His definitions are simply
>>> too restrictive to accommodate those, and he seems to be
>>> having a fit.
>>
>> I'll admit to a really great fit of laughter at that
>> one!
>>
>> You are so thoroughly confused that it is hilarious.
>> The recognized standard definitions say that a
>> quantized
>> signal is digital. You can indeed have a two-level
>> analog signal, but the fact is that the *possible*
>> values are infinite (all values between your two listed
>> ones, for example). You cannot possibly have a digital
>> signal with a continuous range of values (large or
>> small, relative or otherwise).
>>
>> I've cited multiple credible sources that agree with
>> what I say. You can't cite even one. There are none.
>
>There are only two possible values for the output of a hard limiter.
There are an infinite number of errors in your
statement.
An FM signal, such as you specified earlier, does not
encode information as voltage levels.
The phase or frequency contains the information, and a
hard limiter does not restrain the values to only two.
There might in fact be only two, but we don't know that
and the limiter does not assure that.
For a typical FM signal modulated by audio we might well
have an infinite number of possible values after the
signal is passed through a hard limiter. It is also
true that we could modulate it with something else that
has only two values, and then it would be digital.
>Make something of it. OTOH, bu using CMOS logic and varying the power
>supply voltage randomly between the limits of 3 volts and 18 volts, I
>can hive a digital signal an infinite number of values.
That would be funny if you were joking, but Jerry I
realize that you are dead serious.
Lets use, just for this example, an RS-232C interface
definition. We could use some other interface, and it
would always be the same result. But since your voltage
range fits within the range of voltages that are correct
for RS-232 (and few others do) we'll use that.
If your signal varies between +3 and +18 volts, it has
exactly 1 value. That is a space signal. If you want
it to be mark, you can vary it between -3 and -18
volts...
Yes, you do have an infinite number of *voltages*
between 3 and 18, but only one signal value.
Tell me Jerry, do you actually get paid to do
engineering?
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>;
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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Author: Mr.TDate: 01:49 28-08-07
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"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87veb0jm5u.fld@apaflo.com...
> Yes, you do have an infinite number of *voltages*
> between 3 and 18,
Only in theory, in practice nothing is infinite in this universe.
Noise will set the resolution limit.
MrT.
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Author: Floyd L. DavidsonDate: 02:06 28-08-07
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"Mr.T" <MrT@home> wrote:
>"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
>news:87veb0jm5u.fld@apaflo.com...
>> Yes, you do have an infinite number of *voltages*
>> between 3 and 18,
>
>Only in theory, in practice nothing is infinite in this universe.
>Noise will set the resolution limit.
The noise itself has an infinite number of possible
values, and therefore even if the signal itself is
supposed to be just 1 value, add the noise and there are
an infinite number of values.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>;
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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Author: glen herrmannsfeldtDate: 03:50 28-08-07
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Floyd L. Davidson wrote:
> Jerry Avins <jya@ieee.org> wrote:
(snip on analog vs. digital signals)
>>There are only two possible values for the output of a hard limiter.
> There are an infinite number of errors in your
> statement.
> An FM signal, such as you specified earlier, does not
> encode information as voltage levels.
> The phase or frequency contains the information, and a
> hard limiter does not restrain the values to only two.
Previously when I was in these discussions instead of
digital vs. analog it was modulated (and so in need of
a modem) vs. not modulated. Passing a digital signal
through an analog channel is said to require a modulated
carrier. In that case, it is an analog representation
of a digital signal.
> There might in fact be only two, but we don't know that
> and the limiter does not assure that.
> For a typical FM signal modulated by audio we might well
> have an infinite number of possible values after the
> signal is passed through a hard limiter. It is also
> true that we could modulate it with something else that
> has only two values, and then it would be digital.
(snip)
OK, so when is it a direct representation of a digital
signal instead of an analog channel with a modulated
signal? I might believe it for NRZ, but just about
anything else I don't.
> Lets use, just for this example, an RS-232C interface
> definition. We could use some other interface, and it
> would always be the same result. But since your voltage
> range fits within the range of voltages that are correct
> for RS-232 (and few others do) we'll use that.
> If your signal varies between +3 and +18 volts, it has
> exactly 1 value. That is a space signal. If you want
> it to be mark, you can vary it between -3 and -18
> volts...
Say you have a space alien trying to decode the signal.
In this case, as with other NRZ signals, there are two choices:
The higher voltage represents '1', or the lower voltage.
There also needs to be a way to know when the value is there,
usually an external clock signal.
How about this for a digital signal: I take an analog telephone
and say into it either "one" or "zero". That is, the english words.
The information content is digital, but the representation is
pretty definitely analog.
-- glen
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Author: Floyd L. DavidsonDate: 03:54 28-08-07
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glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:
>Floyd L. Davidson wrote:
>
>Previously when I was in these discussions instead of
>digital vs. analog it was modulated (and so in need of
>a modem) vs. not modulated.
Okay...
>Passing a digital signal
>through an analog channel is said to require a modulated
>carrier.
That is not necessarily true. The problem has nothing
to with analog vs digital. It instead a question of
whether DC can be amplified or only AC, and over what
bandwidth, on that analog channel.
>In that case, it is an analog representation
>of a digital signal.
I'm not sure that makes sense for an electrical signal.
A digital representation of an analog signal does (the
result when restored is called quasi-analog though).
However, I do think that your last example, discussed
below, appears to be a valid example of an analog
representation of digital signal, except it is not an
electronic representation...
>> There might in fact be only two, but we don't know that
>> and the limiter does not assure that.
>
>> For a typical FM signal modulated by audio we might well
>> have an infinite number of possible values after the
>> signal is passed through a hard limiter. It is also
>> true that we could modulate it with something else that
>> has only two values, and then it would be digital.
>
>(snip)
>
>OK, so when is it a direct representation of a digital
Any time you encode discrete values from a finite set,
that is digital. Period. Whether it can be passed over
an inherently analog channel or not is fairly
meaningless. The voltage, phase, or whatever that is
encoded with the information may have only a discrete
set of values for the information, but they obviously
take on an infinite number of possible values for the
characteristic itself.
Hence the voltage on a binary system carries only two
values, on and off, but that is the value of the
information. The voltage that is encoded might be +3 to
+15 for an on and -3 to -15 for an off. And when the state
switch from on or off to the opposite value, those
voltages do not change instantly, and they do cover an
infinite number of voltages during that change.
That is an infinite number of possible voltages, but
they have a value of either on or off.
The information values are what makes it a digital signal.
But indeed, you can pass that signal through an analog
amplifier. Depending on the characteristics, it may or
may not destroy the information. Obviously the
amplifier would need to pass DC voltages unless we
encode the information in a way that guarantees some set
minimum time interval between state changes (T1 digital
carrier systems typically do that, for example).
>signal instead of an analog channel with a modulated
>signal? I might believe it for NRZ, but just about
>anything else I don't.
If the digital signal has DC components it can be
modulated onto an analog carrier to pass through an AC
coupled analog channel. It could also be re-encoded
in a manner that will pass through an AC only channel,
and then be transmitted over the same AC coupled analog
channel.
Most physical channels are inherently analog! Wire
cables and fiber optic cables are two examples. Digital
signals are commonly sent via either of them.
>> Lets use, just for this example, an RS-232C interface
>> definition. We could use some other interface, and it
>> would always be the same result. But since your voltage
>> range fits within the range of voltages that are correct
>> for RS-232 (and few others do) we'll use that.
>
>> If your signal varies between +3 and +18 volts, it has
>> exactly 1 value. That is a space signal. If you want
>> it to be mark, you can vary it between -3 and -18
>> volts...
>
>Say you have a space alien trying to decode the signal.
>In this case, as with other NRZ signals, there are two choices:
>The higher voltage represents '1', or the lower voltage.
Yes, but you aren't saying anything of significane to the
rest of the discussion.
>There also needs to be a way to know when the value is there,
>usually an external clock signal.
This is even farther off track. (Not that it isn't
interesting! clock synchronization is a really
fascinating topic in my opinion.)
>How about this for a digital signal: I take an analog telephone
>and say into it either "one" or "zero". That is, the english
words.
>
>The information content is digital, but the representation is
>pretty definitely analog.
The information content encoded and sent electronically
is not digital. There is nothing digital about the
sound of your voice. And while "one" and "two" might be
digital, those are not the values that are encoded and
set over the telephone wires. It is the difference
between "one" and "uno" that is encoded, and that is an
infinite number of variations.
But, I do think you've stated a good case for the analog
representation of a digital signal! The "one/two" code
(like Paul Revere's message) is in fact digital, and it
is being sent over an analog channel, which is the
channel from your mouth to your ear!
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>;
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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Author: glen herrmannsfeldtDate: 07:12 28-08-07
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Floyd L. Davidson wrote:
(I wrote)
>>Floyd L. Davidson wrote:
>>Previously when I was in these discussions instead of
>>digital vs. analog it was modulated (and so in need of
>>a modem) vs. not modulated.
> Okay...
>>Passing a digital signal
>>through an analog channel is said to require a modulated
>>carrier.
> That is not necessarily true. The problem has nothing
> to with analog vs digital. It instead a question of
> whether DC can be amplified or only AC, and over what
> bandwidth, on that analog channel.
(snip)
When DSL started to become popular, there was discussion
that a DSL modem wasn't a modem because the DSL signal
was digital. Everyone (just about) knows that v.90 needs
a modem because it goes through the voice telephone system.
But DSL does use a modulated carrier, and the box is
a modem.
> However, I do think that your last example, discussed
> below, appears to be a valid example of an analog
> representation of digital signal, except it is not an
> electronic representation...
(snip)
> Any time you encode discrete values from a finite set,
> that is digital. Period. Whether it can be passed over
> an inherently analog channel or not is fairly
> meaningless. The voltage, phase, or whatever that is
> encoded with the information may have only a discrete
> set of values for the information, but they obviously
> take on an infinite number of possible values for the
> characteristic itself.
But why phase modulation, for example? Two reasons
that I see. One is that the channel does not have
the appropriate frequency response, and the other is
the need for a clock. Consider 10baseT ethernet.
Phase modulation allows for transformer coupling that
is needed to avoid ground loops and ensure a balanced
signal to avoid EMI problems. Using synchronous
phase modulation allows for the recovery of the clock
from the signal, which is also important.
If, for example, the signal was not modulated and one
decided to send 1000000 zeros in a row, there would be
no way to recover the clock to know how many zeros
were sent. If you can't separate the bits, you are
losing an important part of a digital signal.
> Hence the voltage on a binary system carries only two
> values, on and off, but that is the value of the
> information. The voltage that is encoded might be +3 to
> +15 for an on and -3 to -15 for an off. And when the state
> switch from on or off to the opposite value, those
> voltages do not change instantly, and they do cover an
> infinite number of voltages during that change.
> That is an infinite number of possible voltages, but
> they have a value of either on or off.
> The information values are what makes it a digital signal.
> But indeed, you can pass that signal through an analog
> amplifier. Depending on the characteristics, it may or
> may not destroy the information.
If the information is destroyed, then the signal
didn't get through.
> Obviously the
> amplifier would need to pass DC voltages unless we
> encode the information in a way that guarantees some set
> minimum time interval between state changes (T1 digital
> carrier systems typically do that, for example).
>>signal instead of an analog channel with a modulated
>>signal? I might believe it for NRZ, but just about
>>anything else I don't.
> If the digital signal has DC components it can be
> modulated onto an analog carrier to pass through an AC
> coupled analog channel. It could also be re-encoded
> in a manner that will pass through an AC only channel,
> and then be transmitted over the same AC coupled analog
> channel.
> Most physical channels are inherently analog! Wire
> cables and fiber optic cables are two examples. Digital
> signals are commonly sent via either of them.
Some can pass a digital signal without modulation,
others can't.
(snip)
-- glen
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Author: iswDate: 13:31 28-08-07
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In article <87mywcjdq7.fld@apaflo.com>,
floyd@apaflo.com (Floyd L. Davidson) wrote:
> Most physical channels are inherently analog! Wire
> cables and fiber optic cables are two examples. Digital
> signals are commonly sent via either of them.
I'll probably regret jumping in here, but:
The *message* may be digital, but the *signals* are most definitely
analog.
Isaac
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Author: Bob MyersDate: 13:58 28-08-07
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"isw" <isw@witzend.com> wrote in message
news:isw-00A66F.10310528082007@newsgroups.comcast.net...
> In article <87mywcjdq7.fld@apaflo.com>,
> floyd@apaflo.com (Floyd L. Davidson) wrote:
>
>> Most physical channels are inherently analog! Wire
>> cables and fiber optic cables are two examples. Digital
>> signals are commonly sent via either of them.
>
> I'll probably regret jumping in here, but:
>
> The *message* may be digital, but the *signals* are most definitely
> analog.
The SIGNALS are electrical or optical.
Bob M.
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Author: Floyd L. DavidsonDate: 19:29 28-08-07
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glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:
>Floyd L. Davidson wrote:
>>glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:
>>>Floyd L. Davidson wrote:
>
>>>Previously when I was in these discussions instead of
>>>digital vs. analog it was modulated (and so in need of
>>>a modem) vs. not modulated.
>
>> Okay...
>
>>>Passing a digital signal
>>>through an analog channel is said to require a modulated
>>>carrier.
>
>> That is not necessarily true. The problem has nothing
>> to with analog vs digital. It instead a question of
>> whether DC can be amplified or only AC, and over what
>> bandwidth, on that analog channel.
>(snip)
>
>When DSL started to become popular, there was discussion
>that a DSL modem wasn't a modem because the DSL signal
>was digital. Everyone (just about) knows that v.90 needs
>a modem because it goes through the voice telephone system.
Everyone who thinks that is wrong. A v.90 modem is
digital on both sides, and will not pass through a
"voice telephone system". It requires a *digital*
switching system to work. V.90 is not a D/A-A/D
protocol, it is a digital level encoding scheme.
(Indeed, a lot equipment originally used for 56Kbps
digital services was often called a "modem" by not just
customers, but also by telecommunications people. None
of them were technically modems, they were all level
changers, with digital signals in one side and out the
other in a different, but equally digital, format.)
>But DSL does use a modulated carrier, and the box is
>a modem.
But is that because it has a digital side, or is that
because the bandwidth restrictions of the channel cannot
pass the input signal due to the low frequency
components?
It is a bandwidth problem, and it has nothing at all to
do with digital or analog.
In fact, a v.90 modem sends an entirely digital signal
down that very same line. Of course in the process it
necessarily uses the same bandwidth that on a DSL is
allocated for a normal voice channel, and therefore
while DSL can co-exist separately with POTS the v.90
modem cannot.
>> However, I do think that your last example, discussed
>> below, appears to be a valid example of an analog
>> representation of digital signal, except it is not an
>> electronic representation...
>
>(snip)
>
>> Any time you encode discrete values from a finite set,
>> that is digital. Period. Whether it can be passed over
>> an inherently analog channel or not is fairly
>> meaningless. The voltage, phase, or whatever that is
>> encoded with the information may have only a discrete
>> set of values for the information, but they obviously
>> take on an infinite number of possible values for the
>> characteristic itself.
>
>But why phase modulation, for example?
It has *nothing* do to with whether it is digital or
analog...
>Two reasons
>that I see. One is that the channel does not have
>the appropriate frequency response, and the other is
>the need for a clock.
Phase modulation does not uniquely conserve bandwidth
(Manchester encoding uses twice the bandwidth of NRZ,
for example) nor is it unique in the ability to recover
a clocking rate from the data.
>Consider 10baseT ethernet.
>Phase modulation allows for transformer coupling that
>is needed to avoid ground loops and ensure a balanced
>signal to avoid EMI problems.
Alternate mark inversion (AMI) provides the same
characteristics.
But while all of this is indeed very interesting
stuff... it has *nothing* to do with analog vs. digital
or the definitions of either. I don't see any point to
your discussion.
>Using synchronous
>phase modulation allows for the recovery of the clock
>from the signal, which is also important.
That is one way to do it, but there are others.
>If, for example, the signal was not modulated and one
>decided to send 1000000 zeros in a row, there would be
>no way to recover the clock to know how many zeros
There would be no way *only* if you select an encoding
scheme such as NRZ. Manchester encoding provides for
easy clock recover, but so do other encoding schemes.
>were sent. If you can't separate the bits, you are
>losing an important part of a digital signal.
That is not true. Consider AMI using B8ZS encoding...
>> Hence the voltage on a binary system carries only two
>> values, on and off, but that is the value of the
>> information. The voltage that is encoded might be +3 to
>> +15 for an on and -3 to -15 for an off. And when the state
>> switch from on or off to the opposite value, those
>> voltages do not change instantly, and they do cover an
>> infinite number of voltages during that change.
>
>> That is an infinite number of possible voltages, but
>> they have a value of either on or off.
>
>> The information values are what makes it a digital signal.
>
>> But indeed, you can pass that signal through an analog
>> amplifier. Depending on the characteristics, it may or
>> may not destroy the information.
>
>If the information is destroyed, then the signal
>didn't get through.
Of course. But it has *nothing* to do with the amplifier
being analog. There *are* analog amplifiers that will not
destroy it. (And that is no different for analog data either,
which will also be destroyed if the amplifier does not have
suitable characteristics to pass it.)
>> Obviously the
>> amplifier would need to pass DC voltages unless we
>> encode the information in a way that guarantees some set
>> minimum time interval between state changes (T1 digital
>> carrier systems typically do that, for example).
Don't ignore what has already been made clear!
>>>signal instead of an analog channel with a modulated
>>>signal? I might believe it for NRZ, but just about
>>>anything else I don't.
>
>> If the digital signal has DC components it can be
>> modulated onto an analog carrier to pass through an AC
>> coupled analog channel. It could also be re-encoded
>> in a manner that will pass through an AC only channel,
>> and then be transmitted over the same AC coupled analog
>> channel.
>
>> Most physical channels are inherently analog! Wire
>> cables and fiber optic cables are two examples. Digital
>> signals are commonly sent via either of them.
>
>Some can pass a digital signal without modulation,
>others can't.
But is has nothing to do with analog vs. digital. If the
amplifier cannot handle the signal's bandwidth, it makes no
difference if the signal is analog or digital, it will not
"pass" the data from input to output.
You are trying to impute something to digital that is
actually common to analog as well.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>;
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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Author: Floyd L. DavidsonDate: 20:05 28-08-07
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isw <isw@witzend.com> wrote:
>In article <87mywcjdq7.fld@apaflo.com>,
> floyd@apaflo.com (Floyd L. Davidson) wrote:
>
>> Most physical channels are inherently analog! Wire
>> cables and fiber optic cables are two examples. Digital
>> signals are commonly sent via either of them.
>
>I'll probably regret jumping in here, but:
>
>The *message* may be digital, but the *signals* are most definitely
>analog.
That is not correct. Whether a message is or not
digital is entirely unrelated to whether the signal used
to transmit it is analog or digital (and it can indeed
be either, without regard to the message).
"Message" specifically means a complete set of data
formatted for transmission, and is not related to
analog/digital data signals.
For the term "signal", you can choose from several
definitions (FS-1037C):
signal:
1. Detectable transmitted energy that can
be used to carry information.
2. A time-dependent variation of a
characteristic of a physical phenomenon,
used to convey information.
3. As applied to electronics, any transmitted
electrical impulse.
4. Operationally, a type of message, the text
of which consists of one or more letters,
words, characters, signal flags, visual
displays, or special sounds, with prearranged
meaning and which is conveyed or transmitted
by visual, acoustical, or electrical means.
Hence you can see that using "message" and "signal" in
the same sentence is bound to cause confusion in the
context of this particular discussion. It simply does
not mean what you were thinking of. When used properly
the terms "signal" and "message" would be something like
this, "Our actions are intended to send Congress a
message, and we wish to signal our intense displeasure
with corruption."
But we've been discussing signals that meet either
the 1st or 2nd definition above, and specifically not
numbers 3 or 4.
In context, the signals are either digital or analog,
and which they are depends mostly on whether the data,
or individual parts of the information (message) that
the signal carries, is digital or analog.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>;
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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Author: Floyd L. DavidsonDate: 20:09 28-08-07
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Author: Mr.TDate: 21:43 28-08-07
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"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87r6lojir0.fld@apaflo.com...
> >> Yes, you do have an infinite number of *voltages*
> >> between 3 and 18,
> >
> >Only in theory, in practice nothing is infinite in this universe.
> >Noise will set the resolution limit.
>
> The noise itself has an infinite number of possible
> values,
OK, prove it.
> and therefore even if the signal itself is
> supposed to be just 1 value, add the noise and there are
> an infinite number of values.
Only for those who failed mathematics at high school.
MrT.
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Author: iswDate: 01:38 29-08-07
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In article <87wsvfi4rc.fld@apaflo.com>,
floyd@apaflo.com (Floyd L. Davidson) wrote:
> isw <isw@witzend.com> wrote:
> >In article <87mywcjdq7.fld@apaflo.com>,
> > floyd@apaflo.com (Floyd L. Davidson) wrote:
> >
> >> Most physical channels are inherently analog! Wire
> >> cables and fiber optic cables are two examples. Digital
> >> signals are commonly sent via either of them.
> >
> >I'll probably regret jumping in here, but:
> >
> >The *message* may be digital, but the *signals* are most definitely
> >analog.
>
> That is not correct. Whether a message is or not
> digital is entirely unrelated to whether the signal used
> to transmit it is analog or digital (and it can indeed
> be either, without regard to the message).
You specifically mentioned "wire cables and fiber optic cables", so lets
talk about those and ignore other possible transmission media.
In both of those (as they are actually used in the real world),
communication is accomplished by the propagation along them of
electromagnetic fields; never anything else.
Doesn't matter one whit whether you turn the field on and off, or vary
the amplitude or any other characteristic of it continuously, as a means
of sending a message from one end to the other, those fields can take on
*any value* from the maximum level injected into the cable by the
transmitter down to far below the ambient noise level, depending (for
example) on the length of cable being used. IOW, those signals are,
without exception, *analog*.
Isaac
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