Thanks guys, I appreciate the responses. John "toobs" <johndhancock@gmail.com> wrote in message news:<1111926669.968049.298090@o13g2000cwo.googlegroups.com>...> In my experience, if a minimum phase FIR filter does (doesn't) ring > then the linear phase equivalent of that filter also will (won't) ring. > > Anybody have any counterexamples or else a proof that the above is > always true? > > John
ringing: minimum vs linear phase
Started by ●March 27, 2005
Reply by ●March 28, 20052005-03-28
Reply by ●March 30, 20052005-03-30
Mark wrote:> Eric, > > I agree with your statement and I have a question of more detail. I > agree that a linear phase filter and a min phase filter both can > suffer from ringing due to Gibbs Phenomena (assumming they bith are > similar otherwise, i.e. magnitude response) . My question is this.... > Is it true that the difference will be that in the linear phase > filter case, that the ringing will equally come both before and after > the "step" in time, while in the min phase filter case, the ringing > will all be after the step in time. To be specific, I'm thinking of > low pass filters with step functions passing through them.Yes. It's good to be thinking of that. As an extreme example, linear phase audio filters that boost the LF end sound terrible compared to their minimum phase counterparts. Linear phase as the grail for audio filters is a terribly misguided marketing ploy. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein
Reply by ●March 30, 20052005-03-30
"Bob Cain" <arcane@arcanemethods.com> wrote in message news:d2dnue022ms@enews2.newsguy.com...> > > Mark wrote: >> Eric, >> >> I agree with your statement and I have a question of more detail. I >> agree that a linear phase filter and a min phase filter both can >> suffer from ringing due to Gibbs Phenomena (assumming they bith are >> similar otherwise, i.e. magnitude response) . My question is this.... >> Is it true that the difference will be that in the linear phase >> filter case, that the ringing will equally come both before and after >> the "step" in time, while in the min phase filter case, the ringing >> will all be after the step in time. To be specific, I'm thinking of >> low pass filters with step functions passing through them. > > Yes. It's good to be thinking of that. As an extreme example, linear > phase audio filters that boost the LF end sound terrible compared to their > minimum phase counterparts. Linear phase as the grail for audio filters is > a terribly misguided marketing ploy.Bob, Why would that be? A linear phase filter would delay the entire spectrum equally. What's wrong with that? There must be more to it I should think.... Now, if a linear phase filter is used to direct energy to a bass speaker and the other speakers are driven from *different* filters then the differential delays might be a real issue. In this case having all minimum phase filters would seem to help even though there could be residual delay differences. So, maybe the minimum phase filters are an acceptable compromise? Fred
Reply by ●March 30, 20052005-03-30
Fred Marshall wrote:> "Bob Cain" <arcane@arcanemethods.com> wrote in message > news:d2dnue022ms@enews2.newsguy.com... > >> >>Mark wrote: >> >>>Eric, >>> >>>I agree with your statement and I have a question of more detail. I >>>agree that a linear phase filter and a min phase filter both can >>>suffer from ringing due to Gibbs Phenomena (assumming they bith are >>>similar otherwise, i.e. magnitude response) . My question is this.... >>> Is it true that the difference will be that in the linear phase >>>filter case, that the ringing will equally come both before and after >>>the "step" in time, while in the min phase filter case, the ringing >>>will all be after the step in time. To be specific, I'm thinking of >>>low pass filters with step functions passing through them. >> >>Yes. It's good to be thinking of that. As an extreme example, linear >>phase audio filters that boost the LF end sound terrible compared to their >>minimum phase counterparts. Linear phase as the grail for audio filters is >>a terribly misguided marketing ploy. > > > Bob, > > Why would that be? A linear phase filter would delay the entire spectrum > equally. What's wrong with that? There must be more to it I should > think.... > > Now, if a linear phase filter is used to direct energy to a bass speaker and > the other speakers are driven from *different* filters then the differential > delays might be a real issue. In this case having all minimum phase filters > would seem to help even though there could be residual delay differences. > > So, maybe the minimum phase filters are an acceptable compromise? > > FredOne can always adjust the delays, even if only by displacing the speakers. To keep focus, look at a single speaker. The minimum-phase filter may introduce ringing after a steep edge. We're accustomed to that; drums and gongs behave that way. A little more of the same is so tolerable it's not usually noticed. Linear-phase filters cause ringing both before and after the sharp transition. When the program material telegraphs its punches, it sounds very bad. That's the wrong way to make a tone control. Thunder is the sound of a very big spark. The rumble afterward is often a bunch of echoes. What causes the rumble before? Would you want a bass drum to sound like that? Let's coin a word: preverberation. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 30, 20052005-03-30
"Jerry Avins" <jya@ieee.org> wrote in message news:s6SdnS8mz6pGq9bfRVn-hA@rcn.net...> Fred Marshall wrote: > > "Bob Cain" <arcane@arcanemethods.com> wrote in message > > news:d2dnue022ms@enews2.newsguy.com... > > > >> > One can always adjust the delays, even if only by displacing the > speakers. To keep focus, look at a single speaker. The minimum-phase > filter may introduce ringing after a steep edge. We're accustomed to > that; drums and gongs behave that way. A little more of the same is so > tolerable it's not usually noticed. Linear-phase filters cause ringing > both before and after the sharp transition. When the program material > telegraphs its punches, it sounds very bad. That's the wrong way to make > a tone control. > > Thunder is the sound of a very big spark. The rumble afterward is often > a bunch of echoes. What causes the rumble before? Would you want a bass > drum to sound like that? Let's coin a word: preverberation."Preverb," as I've heard it called, is sometimes used intentionally as a special effect in audio but otherwise is undesirable.
Reply by ●March 31, 20052005-03-31
Fred Marshall wrote:> "Bob Cain" <arcane@arcanemethods.com> wrote in message>>Yes. It's good to be thinking of that. As an extreme example, linear >>phase audio filters that boost the LF end sound terrible compared to their >>minimum phase counterparts. Linear phase as the grail for audio filters is >>a terribly misguided marketing ploy. > > > Bob, > > Why would that be? A linear phase filter would delay the entire spectrum > equally. What's wrong with that? There must be more to it I should > think....Imagine a bass drum hit with a hard, quick percusive attack that initiates it. Boost the bass of that hit with a linear phase filter and you will get bass energy coming out of the drum well before the event that actually generates it. I find this audible as a kind of temporal bluring. Doing equivalent filtering with minimum phase causes all energy to remain about where it belongs. In general it sounds more distinct in time and has better spatial localization in the case of stereo or higher order localization systems. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein
Reply by ●March 31, 20052005-03-31
Bob Cain wrote:> Fred Marshall wrote: > > "Bob Cain" <arcane@arcanemethods.com> wrote in message > > >>Yes. It's good to be thinking of that. As an extreme example,linear> >>phase audio filters that boost the LF end sound terrible comparedto their> >>minimum phase counterparts. Linear phase as the grail for audiofilters is> >>a terribly misguided marketing ploy. > > > > > > Bob, > > > > Why would that be? A linear phase filter would delay the entirespectrum> > equally. What's wrong with that? There must be more to it Ishould> > think.... > > Imagine a bass drum hit with a hard, quick percusive attack > that initiates it ...[snipped more philosophizing about linear vs. minimum phase equalization] I swear, at the next comp.dsp conference, I will personally install a linear vs. minimum phase equalisiation station where everybody that has an interest in this can actually _listen_ to the difference instead of having to philosphize about what might be the difference. Regards, Andor
Reply by ●April 1, 20052005-04-01
Andor wrote:> Bob Cain wrote: > >>Imagine a bass drum hit with a hard, quick percusive attack >>that initiates it ... > > > [snipped more philosophizing about linear vs. minimum phase > equalization]Philosophy? I don't understand your relegation of the question to philosophy when there are clear physical implications about when within a sampled sequence things are heard after filtering. You can even see the effect on a display. That's not philosophy, that's data. I do agree that it needs to be heard to have an opinion on audibility of the effect. While I've done that, it wasn't double blind so I'm not sure how much validity I can claim. If you do set this demo up it would be _very_ instructive to set it up as a double blind demo to first see how many can actually distinguish before counting their impression. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein
Reply by ●April 1, 20052005-04-01
Bob Cain wrote:> Andor wrote: > > Bob Cain wrote: > > > >>Imagine a bass drum hit with a hard, quick percusive attack > >>that initiates it ... > > > > > > [snipped more philosophizing about linear vs. minimum phase > > equalization] > > Philosophy? I don't understand your relegation of the > question to philosophy when there are clear physical > implications about when within a sampled sequence things are > heard after filtering.It is philosphizing (musing) like Aristoteles practiced it: think hard about a physical problem and then come up with a result based solely on "logical" deduction.> You can even see the effect on a > display. That's not philosophy, that's data.In my opinion that's philosophy - seeing data on a display is not necessarily correlated with what you hear. You can muse about what could constitute an audible effect, but the verdict has to be by experiment (and not by what you believe to be logical deduction): setup a blind test and listen.> I do agree that it needs to be heard to have an opinion on > audibility of the effect. While I've done that, it wasn't > double blind so I'm not sure how much validity I can claim.So howcome you are so convinced that linear phase eq "smears" bass drum hits? I believe that this is what your eyes tell you to hear. Another Aristotelian musing could be this: a bass drum hit with a sharp attack transient (click) contains wide band frequency information (although only for very short time period). Minimum phase filters delay each frequency by a different amount, resulting in spreading the short attack time period into a longer period, resulting in a less pronounced attack transient. This argument makes superficial sense in favour of linear phase. However, it is my convinction that no such argument can tell the whole story. I have found that at one time, linear phase eq did a better job than minium phase, and at other times vice versa. Such behaviour is not explainable with simple pre-ringing or phase smearing arguments. Au contraire, I think a proper blind test on linear vs. minium phase eq could shed light on how such effects are perceived by our auditory mechanisms.> If you do set this demo up it would be _very_ instructive > to set it up as a double blind demo to first see how many > can actually distinguish before counting their impression.I would really like to do that one day. As I said, a comp.dsp conference (here in Europe preferably) would be a good start ... Regards, Andor
Reply by ●April 1, 20052005-04-01
snip> > I do agree that it needs to be heard to have an opinion on > > audibility of the effect. While I've done that, it wasn't > > double blind so I'm not sure how much validity I can claim. > > So howcome you are so convinced that linear phase eq "smears" bassdrum> hits? I believe that this is what your eyes tell you to hear. > > Another Aristotelian musing could be this: a bass drum hit with asharp> attack transient (click) contains wide band frequency information > (although only for very short time period). Minimum phase filtersdelay> each frequency by a different amount, resulting in spreading theshort> attack time period into a longer period, resulting in a lesspronounced> attack transient. > > This argument makes superficial sense in favour of linear phase. > > However, it is my convinction that no such argument can tell thewhole> story. I have found that at one time, linear phase eq did a betterjob> than minium phase, and at other times vice versa. Such behaviour isnot> explainable with simple pre-ringing or phase smearing arguments. Au > contraire, I think a proper blind test on linear vs. minium phase eq > could shed light on how such effects are perceived by our auditory > mechanisms. > > snipI agree a listening test would be interesting. But I'll also muse for a bit. My thought experiment is to think about the transient (impulse response) of 5 kHz low pass filters fed with impulses. I classify the filters as min phase vs linear phase and also as sharp cutoff vs gradual cutoff. SHARP CUTOFF FILTERS If the low pass filter has a sharp cutoff, it WILL ring due to Gibbs. A sharp cutoff min phase will post ring. A sharp-cutoff linear phase will pre and post ring. Both sound bad. In order to minimize the ringing, you HAVE TO use a gradual cutoff to prevent Gibbs. So all sharp cut-off filters probably sound bad if the transition band is in the audible frequency range. GRADUAL CUTOFF FILTERS What about gradual cutoff filters? If we now assume a gradual cutoff without Gibbs, which is better, min or linear phase? Standard theory is that the ear is not sensitive to phase information in the context of the relative phase of one frequency to another. I have done this listening test and I believe it. You can take a 1.00 kHz tone and add a 2.01 kHz tone and watch the phases drift through making a radical changes to the scope waveform but you don't hear any change. A gradual filter will have a short impulse response so it cannot make a large change to the delay or phase of any frequency. I think delay becomes audibly only when the delay is so large that the sound is heard as an echo. A gradual cutoff filter cannot create sufficient time or phase change to create an echo. So my hypothisis is.... Sharp cutoff filters will always create echoes. Min phase vs linear phase will only make a difference in the nature of the echoes. Min phase having all post echoes and linear phase have pre and post echoes. To make a "good sounding" filter without echoes, you need to use a gradual cutoff and it doesn't matter if it is min phase or linear phase. The more gradual the frequency response change, the less temporal distortion. Comments Mark>
