Don Pearce wrote:> On Sun, 19 Aug 2007 23:26:16 -0700, dplatt@radagast.org (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. jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
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 wrote:> On Sun, 19 Aug 2007 23:26:16 -0700, dplatt@radagast.org (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. jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
Don Pearce wrote:> On Sun, 19 Aug 2007 23:26:16 -0700, dplatt@radagast.org (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. jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
On Mon, 20 Aug 2007 03:51:54 -0400, Jerry Avins <jya@ieee.org> wrote:>Don Pearce wrote: >> On Sun, 19 Aug 2007 23:26:16 -0700, dplatt@radagast.org (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. d -- Pearce Consulting http://www.pearce.uk.com
Reply by ●August 20, 20072007-08-20
Martin Heffels wrote:> On Sun, 19 Aug 2007 18:14:58 -0700, Radium <glucegen1@gmail.com> wrote: > >> If a digital audio device can play audio back without >> any moving parts, why can't an analog audio device be designed to do >> the same? > > Because if it could, there would be no need to invent digital which has the > advantage of non-moving parts....................Actually, I did invent something along those lines, but I was foolish enough yo leave the plans in my (not yet perfected) time machine, and they disappeared. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
On Mon, 20 Aug 2007 04:16:44 -0400, Jerry Avins <jya@ieee.org> wrote:>Actually, I did invent something along those lines, but I was foolish >enough yo leave the plans in my (not yet perfected) time machine, and >they disappeared.Shame on you! Radium will be very disappointed now. -m- -- Official website "Jonah's Quid" http://www.jonahsquids.co.uk
Reply by ●August 20, 20072007-08-20
Ron N. wrote:> On Aug 19, 8:37 pm, Jerry Avins <j...@ieee.org> wrote: > >>What would you write into that "RAM"? There are no analog bits. > > > Well, some types of RAM bits are stored as analog voltages > on a MOS gate capacitor. I think old CCD devices could > output some measure of the voltage per bit cell. Or you > could consider the charge digital if you could count the > number of electrons in each well. > >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. Limitations: expensive, so delays were very short (a few msecs) but in their heyday digital was still new and therefore expensive too); performance - low sample rate; quality - somewhat noisy. Electronics people loved debating whether such devices were really digital or analog. At least: digital in concept, analog in implementation. Suffice it to say, digital is better in all aspects. Richard Dobson
Reply by ●August 20, 20072007-08-20
Radium wrote:> On Aug 19, 6:08 pm, Jerry Avins <j...@ieee.org> wrote: > > >>Radium wrote: > > >>>This would be a start if I want to decrease the frequency of a video >>>signal without decreasing the playback speed. > > >>Various compression schemes do that with varying degrees of resulting >>quality. > > > I am talking about: > > 1. Decreasing the temporal frequency of the video signal without low- > pass filtering or decreasing the playback speed - an example of which > would be decreasing the rate at which a bird [in the movie] flaps its > wings. Hummingbirds flap their wings too fast for the human eye to > see. So the flap-rate of the wings could be decreased until the > flapping is visible to the human eye - without decreasing the playback > speed of the video. This decrease in flap-rate without slowing > playback is visually-analogous to decreasing the pitch of a recorded > sound without decreasing the playback speed. In this case, low-pass > filter would involve attenuating rapidly-changing images while > amplifying slowly-changing images -- I don't want this. >I confess I am jumping into a thread having just discovered it. There are some mixed metaphors here. There is a video equivalent to audio pitch shifting. think of the latter represetned in the frequency domain (spectrum) - the peak correspindsing to the source partial moves down (or up). the video equivalent is colour cycling or shifting. But most simply, reds would be shifted to orange, green shifted to blue, violet to ultra-violet (and hence llost to view). An alternatyive stratgy is colour rotation using the artists colour wheel, where, ideally, diametrically opposite colours are complementary. There is no equivalent that I know of to colour complemenariness in audio. I ~think~ I get what Radium wants - he wants to be able to modify a recorded scene the way one can modify a CGI virtual scene, e.g. by setting a slower wing flapping rate while leaving other parts of the scene unchanged. As far as I know, computer vision and scene analysis is nowhere near being able to do this. The only audio parallel I can think of is wanting to pitch shift just one instrument in a polyphonic texture, leaving other voices unchanged. With luck, some implementations of Blind Source Separation can sometimes do this (they need the mixed sounds to be very distinct - I have seen one example demonstrated at DaFX); ths difficulties with video I would expect to be order of magnitude greater. Richard Dobson
Reply by ●August 20, 20072007-08-20
Richard Dobson wrote:> Ron N. 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. -- glen
Reply by ●August 20, 20072007-08-20
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. -- glen
