Jerry Avins wrote:> Richard Owlett wrote: > >> Jerry Avins wrote: >> >>> glen herrmannsfeldt wrote: >>> >>> ... >>> >>>> I had a physics lab class once where we measured the impedance, >>>> attenuation, and propagation velocity for different cables. One was >>>> a coax cable with a spiral wound center conductor which increases >>>> its inductance relative to capacitance, for a velocity of about >>>> 0.1c. It was designed for use as a delay line. >>> >>> >>> >>> >>> An interesting feature of that cable is that if you take the length >>> of the stretched-out inner conductor as the length of the cable, The >>> group velocity comes out not much different from RG59U. You could say >>> that the signal takes so long to come our because it gets dizzy along >>> the way. Did the cable have a blue jacket? >>> >>> Jerry >> >> >> >> Hmmm if that's generally true as a first order approximation, it might >> explain why something I tried as an ignorant teenager interested in >> Ham radio _apparently_ worked. I needed/wanted a halfwave dipole. Did >> not have space. Used a couple of handy pieces of Al tubing as long as >> possible. Made up rest of length required with wire loosely wrapped >> around .5->.75 inch form. OK, so that was >40 yrs ago ,] >> As I recall, it did work. > > > Well, a pair of opposed whips is a dipole. An opposed pair of end-loaded > whips is an end-loaded dipole. Why not? It should work! > > JerryI knew of "loaded whips" at the time. What surprised me was that just getting right length of wire worked so well. I had a "gut" feeling that a certain length of wire should "appear longer" if in form of coil rather than stretched out in straight line. [ For perspective, I had a long running argument with my father. I claimed that upper AND lower sidebands were unnecessary. Any AM signal ONLY required the carrier frequency. ]
DSP sound/audio demos
Started by ●November 16, 2003
Reply by ●November 21, 20032003-11-21
Reply by ●November 21, 20032003-11-21
Vladimir Vassilevsky wrote:> > Jerry Avins wrote: > >>>>>>All >>>>>>you have to do with an equalizer is compensate the major non-idealities >>>>>>caused mainly by the speakers and the acoustic environment. >> >>I believe he meant, "All you _can_ (or maybe, ought to) do ...", but he >>can clarify that. > > > The equalizer can significantly flatten the response of an audio system. > I did that many times and the improvement may be very noticeable. > > > >>>- it seems that at least some people are of the opinion that equalizers can >>>be used to correct loudspeaker (or room) response. >> >>Indeed they can. > > > You bet. > > >>No equalizer can flatten the spiky response that shows up if >>you run the response curve slowly enough. > > > Flattening the major spikes is quite simple task for the parametric EQ. > The notch is more difficult to correct because of the limited power > available, however the notches in the response are less noticeable then > the spikes. > > >>>>>You cannot equalize a room, because a room does >>>>>not have a well-defined frequency response. > > > That is correct. However you can equalize the speaker axis emission in > ideal non-echoic room. That makes the speaker sound better in general. > > >>>>If that were germane, one would need different equalization for every >>>>cubic foot of space in the room. The phenomenon is real, but it >>>>matters very little. > > > I have seen acoustic arrays which were pretending to do that. The idea > is similar to the holographic technology. > > >>>The only justification I see for equalizers in PA systems is for feedback >>>suppression. > > > That is done better with LMS feedback cancellation and/or adaptive > notches. > > But what really surprises me in all that arguments about FIRs ans IIRs > that very few people understand that there is no direct relation between > the "ringing" and the phase linearity. The passive RC filter can have > very nonlinear phase, however it exibits no ringing. > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.comMany decades ago I was an "Instrument Tech" for the Chemistry Dept. of an Ivy |League Univ. A routine chore was to "tune" some NMR spectrometers. I recall, with charing, how much time I spent trying to get rid of some "ringing" in the plot of one of the calibration samples. Seems the laws of physics said "more 'ringing' " == "better magnet homogeneity".
Reply by ●November 21, 20032003-11-21
Rick Lyons wrote:> On 16 Nov 2003 04:56:14 -0800, allnor@tele.ntnu.no (Rune Allnor) > wrote: > > >>Hi All. >> >>The last few weeks I have been asked by a few people (neighbours, >>neighbours' kids) what I do for a living. And I find that it's not >>easy to explain verbally what DSP is about. Terms like "Discrete >>Fourier Transforms", "Singular Value Decompositions", "Rayleigh waves" >>and the likes don't do much for lay people, except perhaps establishing >>or reinforcing my already firm reputation as "the mad scientist" of the >>neighbourhood. >> >>So, inspired by this and some remarks Al Clark made in the DSP book thread, >>I've started thinking what demos could be useful to show people what >>at least parts of DSP is about. I assume I have a laptop PC available >>where matlab is installed and that has a microphone and a sound recording >>program. With this system I can record somebody speaking a sentence, >>store the sound to a .wav file that I load into matlab. I then manipulate >>this sound by means of DSP in matlab, and play the manipulated result over >>the PC speaker or headphones. >> >>So, what DSP demos could be included here? Remember, I'm not an audio >>specialist so the most psycho-acoustical stuff would probably best be >>left out. Implementations should not be too difficult either, or at >>least good algorithm recipes should be available. Pitch shifting? >>LPC-errors (somebody told me these things sound like "robot voices" > >>from a 1977 sci-fi movie)? Adding echos/reverbrations? Other things? > >>Rune > > > Hello Mad Scientist, > > an audio demo is a great idea. > > To add to the other suggtestions here: > > I'd start with letting the kids hear a pure tone, > and see its waveform in time, plus a spectral plot. > Tell them the time-domain plot is just like the > position of a plucked guitar string. > > Next let the kids, themselves, change the freq of > the tone to see what the change looks like in time > and in the spectral plot. > > Then let the kids hear and see two tones. Explain > filtering and then filter out one of the tones, > letting the kids see and hear the filtered signal. > > Let the kids experiment. > > Maybe a demo using the telephone DTMF tones would > be useful. All the kids will be familiar with > the DTMF tones. > > You might record a few words of speech and then add > lots of high frequency noise. Let the kids hear > and see the noisy speech signal. > Then start filtering out the high freq noise > and let the kids hear and see the filter output. > Let the kids control how much the noise is attenuated. > They'll see that reducing the noise more and more > (watching the noise spectral magnitudes drop) makes > the speech easier and easier to hear and understand. > > After that, you can show the kids how to > invert a Toeplitz matrix based on cyclotomic > polynomials in tight Gabor frames. > > [-Rick-] >I would suggest a slightly different approach. My idea depends on two unknowns: 1. is it possible 2. is it feasible It also depends on what I think is a reasonable description of your "profession" -- extracting useful signals from noisy environment. Record a mob of kids talking while someone quietly plays wind instrument in background. Play back recording. do black magic Play clean copy of music.
Reply by ●November 23, 20032003-11-23
Richard Owlett <rowlett@atlascomm.net> wrote in message news:<vrta7mkdo3d3ba@corp.supernews.com>...> I would suggest a slightly different approach. > > My idea depends on two unknowns: > 1. is it possible > 2. is it feasible > > It also depends on what I think is a reasonable description of your > "profession" -- extracting useful signals from noisy environment. > > Record a mob of kids talking while someone quietly plays wind > instrument in background. > > Play back recording. > do black magic > Play clean copy of music.If have this weird idea that may or may not work. It does require a synchronized two-channel recording setup such that both channels record the wind instrument but each channel records different people talking. I know of a trick that can be used to filter out what is common between the two channels for parameter estimation purposes, but I don't know if it can be used for signal reconstruction purposes. But then, I have been known to fight windmills... ;) Rune
Reply by ●November 23, 20032003-11-23
Rune Allnor wrote:> "Ban" <XbansuriX@XwebX.de> wrote in message news:<lgMtb.29683$9_.1173558@news1.tin.it>... > > Rune Allnor wrote: > > || Hi All. > > || > > || The last few weeks I have been asked by a few people (neighbours, > > || neighbours' kids) what I do for a living. And I find that it's not > > || easy to explain verbally what DSP is about. Terms like "Discrete > > || Fourier Transforms", "Singular Value Decompositions", "Rayleigh > > || waves" > > > > Hey Rune, > > I have been reading a couple of your questions- > > They were asking "for a living" not interest or hobby. > > If you show off, be aware that there might be a guy in your neighborhood, > > who really does this for a living, then you *are* caught. > > That's true, at least what audio is concerned. There are some people > nearby who apparently have quite a reputation among professional musicians > as "wizards" what sound in concert halls and PA is concerned.Difference is though that you are a professional engineer and can design the equipment - whereas they are end users. Your level of understanding is therefore numerous levels above theirs. By this I mean we can design racing cars and boast about but may well be useless at driving them! Tom
Reply by ●November 24, 20032003-11-24
Tom <somebody@nOpam.com> wrote in message news:<3FC124BA.4A695E08@nOpam.com>...> Rune Allnor wrote: > > > "Ban" <XbansuriX@XwebX.de> wrote in message news:<lgMtb.29683$9_.1173558@news1.tin.it>... > > > Rune Allnor wrote: > > > || Hi All. > > > || > > > || The last few weeks I have been asked by a few people (neighbours, > > > || neighbours' kids) what I do for a living. And I find that it's not > > > || easy to explain verbally what DSP is about. Terms like "Discrete > > > || Fourier Transforms", "Singular Value Decompositions", "Rayleigh > > > || waves" > > > > > > Hey Rune, > > > I have been reading a couple of your questions- > > > They were asking "for a living" not interest or hobby. > > > If you show off, be aware that there might be a guy in your neighborhood, > > > who really does this for a living, then you *are* caught. > > > > That's true, at least what audio is concerned. There are some people > > nearby who apparently have quite a reputation among professional musicians > > as "wizards" what sound in concert halls and PA is concerned. > > Difference is though that you are a professional engineer and can design the equipment - > whereas they are end users. Your level of understanding is therefore numerous levels above > theirs. By this I mean we can design racing cars and boast about but may well be useless at > driving them! > > TomThat's certainly true! Designing DSP stuff and using it are two almost orthogonal diciplines. Still, my ambition is merely to make some sort of gizmo that somehow let laymen and kids get an impression of what I do for a living, in a context they can relate to. Almost all people alive have some relation to sound and and opinion about what sound is. Not so with seismics or sonars, which is what I actually work with. So if I can record some "audio" sounds and manipulate them, then I might be able to convey some sort of impression of what DSP is all about. I will, of course, never impose as an audiologists or a PA wizard. I'll just tell the people that "the sounds we use in seimsics and sonars are a bit different and the processing we do is not quite the same, but everything is aimed at manipulating measured sounds and squeezing all sorts of funny effects out of them, much like what you see in this demo". Some responses in this thread has mentioned various SW packages. In one respect, that's probably better from an engineering point of view. Still, I would very much like to do as much as possible myself. Partly because I think there is lots of useful stuff to learn from it, partly because my experience when I draw with the kids, is that if they see me actually use the pencil and make some marks on the paper, it has a much larger impact than, say, showing them a drawing by Leonardo or Durer and tell them that "if you work hard you might be able to draw like this some day". A home-made demo is more likely to give the impression that I make these things. A canned SW package gives the impression that I use these things. The difference is like working at M$oft versus using windows on your PC at home. Rune
Reply by ●November 24, 20032003-11-24
Here's a simple trick that can also be a fun game too. Record someone saying a short phrase, then reverse the speech in software (should be very easy to do yourself in Mat, etc.). Play back the reversed phrase. Sounds funny, haha! Play it back several times and ask someone to try to exactly speak the reversed phrase. Record that attempt, reverse again and play back. If they did a decent job, the original message will be recognizable, but it will sound like they have a funky accent, speech impediment, etc. Can be entertaining. Just an idea... "Rune Allnor" <allnor@tele.ntnu.no> wrote in message news:f56893ae.0311240444.2a27223c@posting.google.com...> Tom <somebody@nOpam.com> wrote in messagenews:<3FC124BA.4A695E08@nOpam.com>...> > Rune Allnor wrote: > > > > > "Ban" <XbansuriX@XwebX.de> wrote in messagenews:<lgMtb.29683$9_.1173558@news1.tin.it>...> > > > Rune Allnor wrote: > > That's certainly true! Designing DSP stuff and using it are two almost > orthogonal diciplines. Still, my ambition is merely to make some sort > of gizmo that somehow let laymen and kids get an impression of what I do > for a living, in a context they can relate to. Almost all people alive > have some relation to sound and and opinion about what sound is. Not so > with seismics or sonars, which is what I actually work with. > > So if I can record some "audio" sounds and manipulate them, then I might > be able to convey some sort of impression of what DSP is all about. Iwill,> of course, never impose as an audiologists or a PA wizard. I'll just tell > the people that "the sounds we use in seimsics and sonars are a bit > different and the processing we do is not quite the same, but everything > is aimed at manipulating measured sounds and squeezing all sorts of funny > effects out of them, much like what you see in this demo". > > Some responses in this thread has mentioned various SW packages. In one > respect, that's probably better from an engineering point of view. Still, > I would very much like to do as much as possible myself. Partly because I > think there is lots of useful stuff to learn from it, partly because my > experience when I draw with the kids, is that if they see me actually use > the pencil and make some marks on the paper, it has a much larger impact > than, say, showing them a drawing by Leonardo or Durer and tell them that > "if you work hard you might be able to draw like this some day". > > A home-made demo is more likely to give the impression that I make these > things. A canned SW package gives the impression that I use these things. > The difference is like working at M$oft versus using windows on your PC > at home. > > Rune
Reply by ●November 28, 20032003-11-28
> [ For perspective, I had a long running argument with my father. I > claimed that upper AND lower sidebands were unnecessary. Any AM signal > ONLY required the carrier frequency. ] >This is back-to-front surely? You need at least one or other of the sidebands, but the carrier itself doesn't have any information in it really...
Reply by ●November 28, 20032003-11-28
Ian MacArthur wrote:>>[ For perspective, I had a long running argument with my father. I >>claimed that upper AND lower sidebands were unnecessary. Any AM signal >>ONLY required the carrier frequency. ] >> > > > This is back-to-front surely? > You need at least one or other of the sidebands, but the carrier itself > doesn't have any information in it really...Ian, Richard is saying (clearly, as I read it) that he has been very wrong in the past, and gives an example. He offers that as a perspective on the possible worth of his present intuition. Credit him, al least, with modesty. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 29, 20032003-11-29
Richard Dobson wrote:> NOTAM has made an interesting CD (software + sounds + tutorial texts) that may > get close to what you are suggesting: > > http://www.notam02.no/DSP/index-e.html > > It is also called "DSP for Children":Young Geeks more like - shouldn't they be out playing? Tom
