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. 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). Do you have a reference for your definition? -- % Randy Yates % "I met someone who looks alot like you, %% Fuquay-Varina, NC % she does the things you do, %%% 919-577-9882 % but she is an IBM." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
Questions about equivalents of audio/video and digital/analog.
Started by ●August 19, 2007
Reply by ●August 20, 20072007-08-20
Reply by ●August 20, 20072007-08-20
"Don Pearce" <nospam@nospam.com> wrote in message news:46cd3d5b.233043828@news.plus.net...> analogue - a continuous representation of the original signalA CCD is an example of a device which stores information in an analog manner, but non-continuously. Bob M.
Reply by ●August 20, 20072007-08-20
"Floyd L. Davidson" <floyd@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.
Reply by ●August 20, 20072007-08-20
"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. 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.
Reply by ●August 20, 20072007-08-20
Floyd L. Davidson wrote:> nospam@nospam.com (Don Pearce) wrote: >> On Mon, 20 Aug 2007 04:57:03 -0800, floyd@apaflo.com (Floyd L. >> Davidson) wrote: >> >>> Jerry Avins <jya@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. > > A "quantized analogue signal" is digital by definition. > > (Emphasis added) > > 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/The government declares it so it must be true? I can demonstrate a circuit using analog components that transforms a continuous ramp input into a staircase output. Moreover, the output levels can be individually adjusted. Is the output digital? (We're discussing an arbitrary definition here. There is no wrong answer.) Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
Randy Yates <yates@ieee.org> writes:> 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.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). -- % Randy Yates % "The dreamer, the unwoken fool - %% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..." %%% 919-577-9882 % %%%% <yates@ieee.org> % 'Eldorado Overture', *Eldorado*, ELO http://home.earthlink.net/~yatescr
Reply by ●August 20, 20072007-08-20
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.>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.>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). d -- Pearce Consulting http://www.pearce.uk.com
Reply by ●August 20, 20072007-08-20
"Radium" <glucegen1@gmail.com> wrote in message news:1187591359.045722.145790@i38g2000prf.googlegroups.com...> > The purpose of this visual "pitch-shifting" is like a way to record/ > playback/transmit/receive/store supreme-quality video while using the > least bandwidth and storage space necessary when low-pass filtering is > not an option.And as you have been told countless times before, you REALLY need to read up on the basics of compression, and specifically the differences between "lossy" and "lossless" compression, and what forces the differences between these two and what enables the latter. Until you do, you'll never really understand any of this.> Hence, if you want to get decent imagery in a low-bandwidth imaging > device, your best bet is to decrease the spatial frequency because > transferring it into the imaging device.Or use fewer bits per sample, or just fewer bits for certain parts of the information you're trying to capture (for instance, chroma information vs. luma), or remove redundant information. (Think about this: how efficient is it, if we have a section of an image which is just a blank white area, to have each and every pixel there carry information that equates to "I'm white!" "So am I!" "So am I".... and so forth? Just one example to consider...). You can also reduce the temporal frequency in the case of motion video. And these are just the simpler approaches. Bob M.
Reply by ●August 20, 20072007-08-20
On Mon, 20 Aug 2007 11:46:41 -0400, Randy Yates <yates@ieee.org> wrote:>Randy Yates <yates@ieee.org> writes: > >> 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. > >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).Sorry, but that is simply nonsense. A signal that is sampled in time, but not quantized is an analogue signal. It is treated and processed by analogue circuits. For a signal to be digital its sampled levels must be represented by numbers, which are processed mathematically by some sort of microprocessor. The signal can be reconverted to an analogue one later by a D to A. The output of a D to A is still a time-sampled signal, but since it is now a set of varying levels, we again call it an analogue signal. d -- Pearce Consulting http://www.pearce.uk.com
Reply by ●August 20, 20072007-08-20
On Mon, 20 Aug 2007 11:46:41 -0400, Randy Yates <yates@ieee.org> wrote:>Randy Yates <yates@ieee.org> writes: > >> 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. > >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).Sorry, but that is simply nonsense. A signal that is sampled in time, but not quantized is an analogue signal. It is treated and processed by analogue circuits. For a signal to be digital its sampled levels must be represented by numbers, which are processed mathematically by some sort of microprocessor. The signal can be reconverted to an analogue one later by a D to A. The output of a D to A is still a time-sampled signal, but since it is now a set of varying levels, we again call it an analogue signal. d -- Pearce Consulting http://www.pearce.uk.com
