In article <BBDD3065.5C23%rbj@surfglobal.net>, robert bristow-johnson <rbj@surfglobal.net> wrote:>a causal continuous-time filter that doesn't have some sorta perfect delay >elements in it (one constructed from op-amps or other amplification >elements, resistors, capacitors, possibly inductors), that filter cannot >be FIR. it's impulse response is an additive combination of one-sided >exponential and sinusoidal functions. > >now there are (or used to be) these devices that used to be called "bucket >brigade delays" (i think the legit name was "charge-coupled devices" which >operated on sampled analog signals.You forget that the simplest true physical component has a close to perfect delay. It's called a wire. Any non-zero length wire will have a delay constrained by the speed-of-light in the medium (usually Cu or Al surrounded by a insulating dielectric). Before fast A/D's, didn't people use to make filters by using a spool of a few meters or miles of coax? IMHO. YMMV. -- Ron Nicholson rhn AT nicholson DOT com http://www.nicholson.com/rhn/ #include <canonical.disclaimer> // only my own opinions, etc.
DSP sound/audio demos
Started by ●November 16, 2003
Reply by ●November 18, 20032003-11-18
Reply by ●November 18, 20032003-11-18
"Jerry Avins" <jya@ieee.org> wrote in message news:bpb2un$5sr$1@bob.news.rcn.net...> Vladimir Vassilevsky wrote: > > > ... the technical arguments are meaningless in > > the fields of religious wars of audiophiles. > > > ... > > Before discussing technical audio issues, I try to learn if my > interlocutor believes that speakers sound better when driven through > gold-plated welding cable. I don't engage him if he does. Another > disqualifier is ownership of a CD demagnetizer. (I hadn't heard ofthose> until Clay pointed them out.) > > Jerry > -- > Engineering is the art of making what you want from things you canget.>���������������������������������������������������������������������� �>I had not heard of the demagnetizers either, so I did a search. Good Grief (tm). Complete with Japanese, US and Taiwanese patents. That has to say something about the patent system. That is right up there with the proposal from a colleague that speaker cables should have a prime number of strands, except _he_ was joking. Regards Ian
Reply by ●November 18, 20032003-11-18
<Ronald H. Nicholson>; "Jr." <rhn@nojunk.rahul.net> wrote in message news:bpcfet$hj9$1@blue.rahul.net...> In article <BBDD3065.5C23%rbj@surfglobal.net>, > robert bristow-johnson <rbj@surfglobal.net> wrote: > >a causal continuous-time filter that doesn't have some sortaperfect delay> >elements in it (one constructed from op-amps or other amplification > >elements, resistors, capacitors, possibly inductors), that filtercannot> >be FIR. it's impulse response is an additive combination ofone-sided> >exponential and sinusoidal functions. > > > >now there are (or used to be) these devices that used to be called"bucket> >brigade delays" (i think the legit name was "charge-coupleddevices" which> >operated on sampled analog signals. > > You forget that the simplest true physical component has a close > to perfect delay. It's called a wire. > > Any non-zero length wire will have a delay constrained by the > speed-of-light in the medium (usually Cu or Al surrounded by a > insulating dielectric). > > Before fast A/D's, didn't people use to make filters by using aspool> of a few meters or miles of coax? > > > IMHO. YMMV. > -- > Ron Nicholson rhn AT nicholson DOT comhttp://www.nicholson.com/rhn/> #include <canonical.disclaimer> // only my own opinions, etc.Using a length of coax as a delay line has been used in RF signal generators as a discriminator to improve phase noise. Another analog example would be a SAW filter. Sawtek used to do "SAW Non-Dispersive Delay Lines", and dispersive ones for pulse expansion/compression radars. Regards Ian
Reply by ●November 18, 20032003-11-18
Vladimir Vassilevsky wrote:> > Andor wrote: > >>>I always used to think that the purpose of an audio equalizer is to >>>compensate the transfer function nulls with the poles and the poles with >>>the nulls in the way that the resultant overall response is flat. >> >>I'm not quite sure what you mean - which zeroes and poles do you want to >>compensate? Audio equalisation as I see it refers to changing spectral >>balance ("timbre") of musical (or perhaps motion picture) material. > > > There is no need to change the timbre. The timbre is not going to be any > better then originally designed by the professional sound producer.And how does the original professional sound producer design the timbre? By careful arrangement of instruments and with a tool called "audio equalizer".> All > you have to do with an equalizer is compensate the major non-idealities > caused mainly by the speakers and the acoustic environment.These are exactly the kind of corrections you _cannot_ do with an equalizer. "non-idealities" in speakers and acoustic environment are results of non-linear distortion, usually caused by reflections inside the speaker cabinet and off the walls. There is a simple way of showing this: Try to get a frequency response of a room (or a speaker) with a microphone. Move the microphone half a meter and get a new frequency response. These two frequency responses will have very little in common, because reflections cause different phase cancellations at every position in the room (this is not just guessing, I have actually done many such measurements). You cannot equalize a room, because a room does not have a well-defined frequency response. Similarly, "bent" frequency responses of speakers as a result of phase cancellation due to reflections inside the speaker cabinet are not equalizable - you cannot, by boosting or cutting a certain band influence reflection characteristics.>>It can >>be used correctively or artistically, and is usually the domain of live and >>studio recording, mixing and mastering engineers. > > > Using the equalizer either creatively or correctively requires taking > measurementsNo. It requires listening.> and having at least professional-like experience. > There is no way an amateur can tune correctly 31-band 1/3 octave or > 5-band parametric equalizer by perception.I agree - but nobody was talking about amateurs. Professional audio equalizers are designed for professional audio engineers.>>Heck, it's what you do when you crank up the bass on your stereo - just a >>little more sophisticated, depending on the device you use. > > > Most of people are just making a V-shaped equalization curve boosting > high and low frq. The result is an awful sound.Also true. In fact, you can just hit the "Loudness" button, it will make a V-shaped equalizer for you. A well-designed "Loudness" function would be a dynamic equalizer which adjusts its curve according to signal energy.> VLVRegards, Andor
Reply by ●November 18, 20032003-11-18
Andor Bariska wrote:> Vladimir Vassilevsky wrote:...>> There is no need to change the timbre. The timbre is not going to be any >> better then originally designed by the professional sound producer. > > > And how does the original professional sound producer design the timbre? > By careful arrangement of instruments and with a tool called "audio > equalizer". > >> All >> you have to do with an equalizer is compensate the major non-idealities >> caused mainly by the speakers and the acoustic environment. > > > These are exactly the kind of corrections you _cannot_ do with an > equalizer. "non-idealities" in speakers and acoustic environment are > results of non-linear distortion, usually caused by reflections inside > the speaker cabinet and off the walls.Audio mumbo jumbo! Non-linear distortion (i.e. harmonic generation) and reflection are not at all related. It's a waste of money to try to improve a distorting speaker by buying an equalizer. Buy a good speaker instead.> There is a simple way of showing this: > Try to get a frequency response of a room (or a speaker) with a > microphone. Move the microphone half a meter and get a new frequency > response. These two frequency responses will have very little in common, > because reflections cause different phase cancellations at every > position in the room (this is not just guessing, I have actually done > many such measurements). You cannot equalize a room, because a room does > not have a well-defined frequency response.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.> > Similarly, "bent" frequency responses of speakers as a result of phase > cancellation due to reflections inside the speaker cabinet are not > equalizable - you cannot, by boosting or cutting a certain band > influence reflection characteristics.You can, however, build a better cabinet. ... Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 18, 20032003-11-18
Ronald wrote: (snip)> You forget that the simplest true physical component has a close > to perfect delay. It's called a wire.> Any non-zero length wire will have a delay constrained by the > speed-of-light in the medium (usually Cu or Al surrounded by a > insulating dielectric).> Before fast A/D's, didn't people use to make filters by using a spool > of a few meters or miles of coax?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. Color television sets traditionally had a delay line to correct for the different delay between the chrominance and luminance signals. Maybe they use digital filters now and don't need to do that. The comb filter to separate the chrominance and luminance requires a delay of one scan line, too long to do with a coax cable. In the analog days that was done with a SAW (surface acoustic wave) device, now likely done with a digital delay. -- glen
Reply by ●November 18, 20032003-11-18
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. > > > > > > These are exactly the kind of corrections you _cannot_ do with an > > equalizer. "non-idealities" in speakers and acoustic environment are > > results of non-linear distortion, usually caused by reflections inside > > the speaker cabinet and off the walls. > > Audio mumbo jumbo! Non-linear distortion (i.e. harmonic generation) and > reflection are not at all related.Reflections cause phase-cancellation, which cause notch-filter-type behaviour in a frequency response. This is non-linear, because it cannot be compensated by a linear system (ok, perhaps that's my definition). I definitely did not mean harmonic generation (although that is non-linear also).> It's a waste of money to try to > improve a distorting speaker by buying an equalizer. Buy a good speaker > instead.Yes, that's what I'm saying! I was trying to point this out to Vladimir, who said:> >> All > >> you have to do with an equalizer is compensate the major non-idealities > >> caused mainly by the speakers and the acoustic environment.- it seems that at least some people are of the opinion that equalizers can be used to correct loudspeaker (or room) response.> > > There is a simple way of showing this: > > Try to get a frequency response of a room (or a speaker) with a > > microphone. Move the microphone half a meter and get a new frequency > > response. These two frequency responses will have very little in common, > > because reflections cause different phase cancellations at every > > position in the room (this is not just guessing, I have actually done > > many such measurements). You cannot equalize a room, because a room does > > not have a well-defined frequency response. > > 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.Well Jerry, that's exactly the problem. In one spot you have to much low end (usually in niches in corners or under balconies), in another you have a wide notch around 1kHz, etc. It matters very much (enough so for acoustics consultants to earn a living) and the fact remains: you cannot rectify problems like that with an equalizer. The only justification I see for equalizers in PA systems is for feedback suppression.> > Similarly, "bent" frequency responses of speakers as a result of phase > > cancellation due to reflections inside the speaker cabinet are not > > equalizable - you cannot, by boosting or cutting a certain band > > influence reflection characteristics. > > You can, however, build a better cabinet.Right. Or build a more suited room with acoustic treatment for that case. Regards, Andor
Reply by ●November 18, 20032003-11-18
"Andor" <an2or@nospam.com> wrote in message news:3fba79ab_2@news.tiscalinet.ch...> Jerry Avins wrote: > ... > > >> All > > >> you have to do with an equalizer is compensate the majornon-idealities> > >> caused mainly by the speakers and the acoustic environment. > > > > > > > > > These are exactly the kind of corrections you _cannot_ do with an > > > equalizer. "non-idealities" in speakers and acoustic environment are > > > results of non-linear distortion, usually caused by reflections inside > > > the speaker cabinet and off the walls. > > > > Audio mumbo jumbo! Non-linear distortion (i.e. harmonic generation) and > > reflection are not at all related. > > Reflections cause phase-cancellation, which cause notch-filter-type > behaviour in a frequency response. This is non-linear, because it cannotbe> compensated by a linear system (ok, perhaps that's my definition). I > definitely did not mean harmonic generation (although that is non-linear > also).Sorry, a notch filter is a linear operation. In theory, it can be compensated for with a linear filter with an inverse characteristic. Whether or not it's "easy" to compensate for a specific notch with available filters is another question.> Yes, that's what I'm saying! I was trying to point this out to Vladimir,who> said: > > > >> All > > >> you have to do with an equalizer is compensate the majornon-idealities> > >> caused mainly by the speakers and the acoustic environment. > > - it seems that at least some people are of the opinion that equalizerscan> be used to correct loudspeaker (or room) response.Sound contractors do that all the time using an RTA.> > > > There is a simple way of showing this: > > > Try to get a frequency response of a room (or a speaker) with a > > > microphone. Move the microphone half a meter and get a new frequency > > > response. These two frequency responses will have very little incommon,> > > because reflections cause different phase cancellations at every > > > position in the room (this is not just guessing, I have actually done > > > many such measurements). You cannot equalize a room, because a roomdoes> > > not have a well-defined frequency response. > > > > 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. > > Well Jerry, that's exactly the problem. In one spot you have to much lowend> (usually in niches in corners or under balconies), in another you have a > wide notch around 1kHz, etc. It matters very much (enough so for acoustics > consultants to earn a living) and the fact remains: you cannot rectify > problems like that with an equalizer.Sure, you cannot perfectly correct a room for all locations, but you can improve the frequency response for a large number of locations, perhaps even the majority of seats.> The only justification I see for equalizers in PA systems is for feedback > suppression.Of course, if the room was perfectly flat, there would be no dominant frequency to feed back! In theory, you would have no feedback until all of the sudden, every frequency would feed back. When you equalize for feedback suppression, you care correcting the system frequency response. When this is done right, this also tends to correct the room frequency response (OK, also microphone/speaker frequency response).
Reply by ●November 18, 20032003-11-18
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 -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 18, 20032003-11-18
Andor 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. >>> >>> >>>These are exactly the kind of corrections you _cannot_ do with an >>>equalizer. "non-idealities" in speakers and acoustic environment are >>>results of non-linear distortion, usually caused by reflections inside >>>the speaker cabinet and off the walls. >> >>Audio mumbo jumbo! Non-linear distortion (i.e. harmonic generation) and >>reflection are not at all related. > > > Reflections cause phase-cancellation, which cause notch-filter-type > behaviour in a frequency response. This is non-linear, because it cannot be > compensated by a linear system (ok, perhaps that's my definition). I > definitely did not mean harmonic generation (although that is non-linear > also).How so? Unless the signal is nulled completely, there's something there to work with. Anyway, notch filtering is a linear operation.> > >>It's a waste of money to try to >>improve a distorting speaker by buying an equalizer. Buy a good speaker >>instead. > > > Yes, that's what I'm saying! I was trying to point this out to Vladimir, who > said: > > >>>>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.> > > - 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. For a dead room, one can add a bit of reverb. For a room that absorbs highs in carpets and upholstered furniture, you can boost the highs. Speakers are another matter. Cheap ones can have their overall responses flattened, but better ones will be pretty flat to start with. No equalizer can flatten the spiky response that shows up if you run the response curve slowly enough. (Sleazy manufacturers run their responses too fast for spikes to show, then advertise the curves as "unaveraged".)>>>>There is a simple way of showing this: >>> >>>Try to get a frequency response of a room (or a speaker) with a >>>microphone. Move the microphone half a meter and get a new frequency >>>response. These two frequency responses will have very little in common, >>>because reflections cause different phase cancellations at every >>>position in the room (this is not just guessing, I have actually done >>>many such measurements). You cannot equalize a room, because a room does >>>not have a well-defined frequency response. >> >>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. > > > Well Jerry, that's exactly the problem. In one spot you have to much low end > (usually in niches in corners or under balconies), in another you have a > wide notch around 1kHz, etc. It matters very much (enough so for acoustics > consultants to earn a living) and the fact remains: you cannot rectify > problems like that with an equalizer.We agree on that: you need to treat the room, not the signal.> > The only justification I see for equalizers in PA systems is for feedback > suppression. > > >>>Similarly, "bent" frequency responses of speakers as a result of phase >>>cancellation due to reflections inside the speaker cabinet are not >>>equalizable - you cannot, by boosting or cutting a certain band >>>influence reflection characteristics. >> >>You can, however, build a better cabinet. > > > Right. Or build a more suited room with acoustic treatment for that case. > > Regards, > AndorJerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
