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Some questions on digital filter design
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I?am?working?on?numerical?modeling?of?CCW?and?am?at?the?point?that?I?need?to?write?the?code?to?implement?twin?pass?band?tuning.??As?this?is?NOT?seismic?processing?I?pulled?a?small?stack?of?my?EE?DSP?classics?and?started?reading?them.
I?have?always?found?the?descriptions?of?digital?filter?design?in?the?EE?literature?baffling?complex.??As?seismic?is?done?in?recorded?time?it?has?a?great?deal?of?latitude?in?implementation?that?a?real?time?DSP?implementation??lacks.??So?I?presumed?that?the?reason?lay?in?the?real?time?constraint. Yesterday?I?realized?that?the?design??of?a?static?filter?is?completely?trivial.??Specify?the?frequency?domain?characteristics?and?back?transform?to?the?time?domain.??The?impulse?response?is?the?taps?for?any?arbitrary?filter.??I?also?noticed?that?the?filters?in?the?examples?were?zero?phase?filters. In?seismic?we?always?use?zero?phase?(aka?"linear?phase"?in?EE?jargon)??filters?as?interpreting?a?symmetric?waveform?is?much?easier. The?first?step?in?seismic?processing?is?called?"designature".??This?consists?of?using?a?recording?of?the??system?impulse?response?to?create?an?all?pass?filter?which?removes?the?phase?imposed?by?causality.??Typically?the?recording?system?impulse?response?is?measured?and??then?the?phase?of?the?source?is?recorded?for?marine?work?using?arrays?of?air?guns. Analog?filters?are?minimum?phase?as?are?all?physical?processes.??But?the?digital?design?examples?I?saw?were?zero?phase?with?a?symmetric?impulse?response.??This?leads?to?a?non-physical?result.??The?filter?output?begins?*before*?the?input?arrives.??I?find?that?rather?hard?to?justify?in?a?communication?system.??A?quick?check?of?the?indices?revealed?that?except?for?a?very?brief?mention?of?minimum?phase?and?causality?the?issue?is?completely?ignored.??Oppenheim?and?Schafer?devote?a?few?page?and?Rabiner??and?Gold?a?paragraph?before?dismissing?the?matter. Another text made no mention of it at all. Would?a?DSO?which?responded?to?an?impulse?showing?the?trace?varying?*before*?the?peak?of?the?impulse?be?acceptable???I?can't?imagine?why?anyone?would?accept?that. So?why?should?it?be?acceptable?in?a?communication?system???Can?anyone?elucidate?the?matter? Have?Fun! Reg |
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What texts are you using?
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DaveD KC0WJN ============================== All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994) ============================== On Jul 6, 2024, at 09:54, Reginald Beardsley via groups.io <pulaskite@...> wrote: |
开云体育Look at the Weaver method of SSB generation. An easy way to make a tunable BP filter using LP digital filters and DDS oscillator with I/Q outputs. 73 – Mike ? Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 908-902-3831 ? -----Original Message----- ? I?am?working?on?numerical?modeling?of?CCW?and?am?at?the?point?that?I?need?to?write?the?code?to?implement?twin?pass?band?tuning.??As?this?is?NOT?seismic?processing?I?pulled?a?small?stack?of?my?EE?DSP?classics?and?started?reading?them. ? I?have?always?found?the?descriptions?of?digital?filter?design?in?the?EE?literature?baffling?complex.??As?seismic?is?done?in?recorded?time?it?has?a?great?deal?of?latitude?in?implementation?that?a?real?time?DSP?implementation??lacks.??So?I?presumed?that?the?reason?lay?in?the?real?time?constraint. ? Yesterday?I?realized?that?the?design??of?a?static?filter?is?completely?trivial.??Specify?the?frequency?domain?characteristics?and?back?transform?to?the?time?domain.??The?impulse?response?is?the?taps?for?any?arbitrary?filter.??I?also?noticed?that?the?filters?in?the?examples?were?zero?phase?filters. ? In?seismic?we?always?use?zero?phase?(aka?"linear?phase"?in?EE?jargon)??filters?as?interpreting?a?symmetric?waveform?is?much?easier. ? The?first?step?in?seismic?processing?is?called?"designature".??This?consists?of?using?a?recording?of?the??system?impulse?response?to?create?an?all?pass?filter?which?removes?the?phase?imposed?by?causality.??Typically?the?recording?system?impulse?response?is?measured?and??then?the?phase?of?the?source?is?recorded?for?marine?work?using?arrays?of?air?guns. ? Analog?filters?are?minimum?phase?as?are?all?physical?processes.??But?the?digital?design?examples?I?saw?were?zero?phase?with?a?symmetric?impulse?response.??This?leads?to?a?non-physical?result.??The?filter?output?begins?*before*?the?input?arrives.??I?find?that?rather?hard?to?justify?in?a?communication?system.??A?quick?check?of?the?indices?revealed?that?except?for?a?very?brief?mention?of?minimum?phase?and?causality?the?issue?is?completely?ignored.??Oppenheim?and?Schafer?devote?a?few?page?and?Rabiner??and?Gold?a?paragraph?before?dismissing?the?matter.? Another text made no mention of it at all. ? Would?a?DSO?which?responded?to?an?impulse?showing?the?trace?varying?*before*?the?peak?of?the?impulse?be?acceptable???I?can't?imagine?why?anyone?would?accept?that. ? So?why?should?it?be?acceptable?in?a?communication?system???Can?anyone?elucidate?the?matter? ? Have?Fun! Reg ? ? ? |
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Reg, my apologies, but I'm confused as to what you are trying to say. It looks to me as though you are discussing a standard Finite-Impulse-Response (FIR) filter, which can be thought of as a physical realization of a convolution integral, in which the input signal is convolved with the impulse response of the filter being realized. I don't know what you mean when you say "the filter output begins *before* the input arrives." The filter output is not starting *before* the signal arrives -- it starts *the moment* the signal arrives.? If you were to connect the filter's input and output signals to two channels of a scope and then generate, as an input, a gated signal, you'd see on the output channel a filtered version of that gated signal that looks like it has been delayed, in time, by half the number of FIR taps (actually, the delay is (N-1/)2, where N is the number of taps). My apologies if I am misinterpreting the point you are trying to make. Best regards, - Jeff, k6jca
On Saturday, July 6, 2024 at 06:54:36 AM PDT, Reginald Beardsley via groups.io <pulaskite@...> wrote:
I?am?working?on?numerical?modeling?of?CCW?and?am?at?the?point?that?I?need?to?write?the?code?to?implement?twin?pass?band?tuning.??As?this?is?NOT?seismic?processing?I?pulled?a?small?stack?of?my?EE?DSP?classics?and?started?reading?them. I?have?always?found?the?descriptions?of?digital?filter?design?in?the?EE?literature?baffling?complex.??As?seismic?is?done?in?recorded?time?it?has?a?great?deal?of?latitude?in?implementation?that?a?real?time?DSP?implementation??lacks.??So?I?presumed?that?the?reason?lay?in?the?real?time?constraint. Yesterday?I?realized?that?the?design??of?a?static?filter?is?completely?trivial.??Specify?the?frequency?domain?characteristics?and?back?transform?to?the?time?domain.??The?impulse?response?is?the?taps?for?any?arbitrary?filter.??I?also?noticed?that?the?filters?in?the?examples?were?zero?phase?filters. In?seismic?we?always?use?zero?phase?(aka?"linear?phase"?in?EE?jargon)??filters?as?interpreting?a?symmetric?waveform?is?much?easier. The?first?step?in?seismic?processing?is?called?"designature".??This?consists?of?using?a?recording?of?the??system?impulse?response?to?create?an?all?pass?filter?which?removes?the?phase?imposed?by?causality.??Typically?the?recording?system?impulse?response?is?measured?and??then?the?phase?of?the?source?is?recorded?for?marine?work?using?arrays?of?air?guns. Analog?filters?are?minimum?phase?as?are?all?physical?processes.??But?the?digital?design?examples?I?saw?were?zero?phase?with?a?symmetric?impulse?response.??This?leads?to?a?non-physical?result.??The?filter?output?begins?*before*?the?input?arrives.??I?find?that?rather?hard?to?justify?in?a?communication?system.??A?quick?check?of?the?indices?revealed?that?except?for?a?very?brief?mention?of?minimum?phase?and?causality?the?issue?is?completely?ignored.??Oppenheim?and?Schafer?devote?a?few?page?and?Rabiner??and?Gold?a?paragraph?before?dismissing?the?matter.? Another text made no mention of it at all. Would?a?DSO?which?responded?to?an?impulse?showing?the?trace?varying?*before*?the?peak?of?the?impulse?be?acceptable???I?can't?imagine?why?anyone?would?accept?that. So?why?should?it?be?acceptable?in?a?communication?system???Can?anyone?elucidate?the?matter? Have?Fun! Reg |
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This?is?a?general?reply?to?Jeff,?Mike?and?Dave.?I?initially?looked?at:
Digital?Design?Handbook Fred?J.?Taylor Marcel?Dekker?1983 Digital?Signal?Processing Oppenheim?and?Shafer Prentice-Hall?1975 Theory?and?Application?of?Digital?Signal?Processing Rabiner?and?Gold Prentice-Hall?1975 Digital?Signal?Processing?with?Kernel?Method Rojo-Alvarez?et?al Wiley/IEEE?2018 Advanced?Digital?Signal?Processing and?Noise?Reduction Vaseghi Wiley?4th?ed?2008 ?Subsequent?to?the?responses?I?checked: Spectral?Analysis?and?Time?Series Priestly Academic?Press?1981 Continuous?a?Signals?and?System?Analysis?and?Discrete McGillem?and?Cooper Holt,?Reinhart?and?Winston?1974 None?of?them?properly?discuss?the?issue?of?causality. I?did?NOT?look?at?any?of?the?many?monographs?by?Enders?Robinson,?Robinson?&?Treitel?or?John?H.?Karl?as?I?know?they?have?the?matter?stated?very?clearly.?Robinson?and?Treitel?were?members?of?Norbert?Weiner's?Geophysical?Analysis?Group?at?MIT?and?founded?the?entire?basis?of?DSP.?I?spent?4?years?at?UT?Austin?under?another?member?of?the?GAG,?Milo?Backus.?Robinson?performed?the?first?digital?deconvolution?problem?in?1952?using?pencil,?paper?and?a?desk?calculator.??Robinson?has?pride?of?place?as?the?first?person?to?apply?DSP?to?data. Causality?requires?that?the?real?and?imaginary?parts?be?a?Hilbert?transform?pair.?This?is?well?stated?in: The?Fourier?Integral?and?Some?of?Its?Applications Ronald?Bracewell McGraw-Hill?2nd?ed?1978 Causality?simply?states?that?there?is?no?output?prior?to?the?input.?If?a?filter?is?not?causal?it?produces?output?before?the?event.?The?EE?community?appears?to?consistently?label?a?zero?phase?signal?as?linear?phase?with?a?phase?delay.?As?Bracewell?provides?a?proof?and?I?spent?2?semesters?studying?Churchill's?"Operational?Mathematics"?under?Bill?Guy?in?"Integral?Transforms"?at?Austin?in?addition?to?the?semester?I?spent?with?Bracewell?in?"Linear?Systems",?if?the?EE?community?wants?to?redefine?the?math?they?may.?I?shall?stick?to?what?the?mathematicians?wrote. Have?Fun! Reg |
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Good answer. But, dang, I now have to peruse those.
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DaveD KC0WJN ============================== All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994) ============================== On Jul 6, 2024, at 12:37, Reginald Beardsley via groups.io <pulaskite@...> wrote: |
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Daniel Marks
If you want something simple to implement you can use what I did in the fldigi version of SCAMP: look at the? int scamp::rx_process(const double *buf, int len) method.? It implements a simple circular buffer filter, which has a sinc-like response but its frequency may be moved around dynamically.? I use a different approach in my guitar pedal code: for example look at the "DSP_TYPE_WAH" filter effect.? This uses a dynamically changed bandpass filter based on the position of a foot pedal, and does some simple interpolation to move the center frequency around by changing the coefficients of a digital biquad filter.? All digital filters are implemented with a delay, and so none are "noncausal."? There is a compromise between group delay, which is the amount of lag that the filter applies to the signal and the sharpness of the filter.? A "minimum phase" filter minimizes this delay and has the property that the real and imaginary parts are related by the Hilbert transform.? A filter can be expressed as a cascade of a minimum phase filter and an all-pass filter. Dan On Sat, Jul 6, 2024 at 8:54?AM Reginald Beardsley via <pulaskite=yahoo.com@groups.io> wrote: I?am?working?on?numerical?modeling?of?CCW?and?am?at?the?point?that?I?need?to?write?the?code?to?implement?twin?pass?band?tuning.??As?this?is?NOT?seismic?processing?I?pulled?a?small?stack?of?my?EE?DSP?classics?and?started?reading?them. |
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Most of my DSP work was in the early 70's using discrete chips. It was not even called DSP then. Built both FIT and IIR filters. At the time chips and DACs and ADCs were slow. That was OK as we were working on detecting and classifying submarine signals at acoustic frequencies. In fact, the first couple of filters that I built used serial arithmetic using chips from Rockwell Collins. Things got a lot nicer when AMD came out with parallel multipliers. All my filters were built with cascaded second order sections of the Elliptic design. Also, we used the Weaver method to make them tunable. Regards - Mike
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Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 908-902-3831 -----Original Message-----
From: qex@groups.io <qex@groups.io> On Behalf Of Reginald Beardsley via groups.io Sent: Saturday, July 6, 2024 12:37 PM To: qex@groups.io Subject: Re: [qex] Some questions on digital filter design This is a general reply to Jeff, Mike and Dave. I initially looked at: Digital Design Handbook Fred J. Taylor Marcel Dekker 1983 Digital Signal Processing Oppenheim and Shafer Prentice-Hall 1975 Theory and Application of Digital Signal Processing Rabiner and Gold Prentice-Hall 1975 Digital Signal Processing with Kernel Method Rojo-Alvarez et al Wiley/IEEE 2018 Advanced Digital Signal Processing and Noise Reduction Vaseghi Wiley 4th ed 2008 Subsequent to the responses I checked: Spectral Analysis and Time Series Priestly Academic Press 1981 Continuous a Signals and System Analysis and Discrete McGillem and Cooper Holt, Reinhart and Winston 1974 None of them properly discuss the issue of causality. I did NOT look at any of the many monographs by Enders Robinson, Robinson & Treitel or John H. Karl as I know they have the matter stated very clearly. Robinson and Treitel were members of Norbert Weiner's Geophysical Analysis Group at MIT and founded the entire basis of DSP. I spent 4 years at UT Austin under another member of the GAG, Milo Backus. Robinson performed the first digital deconvolution problem in 1952 using pencil, paper and a desk calculator. Robinson has pride of place as the first person to apply DSP to data. Causality requires that the real and imaginary parts be a Hilbert transform pair. This is well stated in: The Fourier Integral and Some of Its Applications Ronald Bracewell McGraw-Hill 2nd ed 1978 Causality simply states that there is no output prior to the input. If a filter is not causal it produces output before the event. The EE community appears to consistently label a zero phase signal as linear phase with a phase delay. As Bracewell provides a proof and I spent 2 semesters studying Churchill's "Operational Mathematics" under Bill Guy in "Integral Transforms" at Austin in addition to the semester I spent with Bracewell in "Linear Systems", if the EE community wants to redefine the math they may. I shall stick to what the mathematicians wrote. Have Fun! Reg |
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Is it really a breach of causality if the output
that displays the breach doesn't actually occur until some processing delay after the input that caused the output? I remember discussing this stuff at length some 50 years ago in a class on linear systems.... all I remember is discussing it, not what we decided, nor how we got there. I do recall that simplicity in the math required that certain apparently non-causal things would appear in the results. There is a whole lot of blue ink underlining way too much, in the section on convolution of the impulse function, and causality, in my copy of Linear Systems Analysis by Liu & Liu... which, for me, usually meant I was hopelessly confused... -Chuck Harris On Sat, 6 Jul 2024 16:37:12 +0000 (UTC) "Reginald Beardsley via groups.io" <pulaskite@...> wrote: ?This?is?a?general?reply?to?Jeff,?Mike?and?Dave.?I?initially?looked |
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Be happy I left out the list of books by Robinson, et al. And the 2D image processing monographs of which I have a large number. On Saturday, July 6, 2024 at 12:02:10 PM CDT, Dave Daniel <kc0wjn@...> wrote: Good answer. But, dang, I now have to peruse those. DaveD KC0WJN ============================== All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994) ============================== > On Jul 6, 2024, at 12:37, Reginald Beardsley via groups.io <pulaskite@...> wrote: > > ? This is a general reply to Jeff, Mike and Dave. I initially looked at: > > Digital Design Handbook > Fred J. Taylor > Marcel Dekker 1983 > > Digital Signal Processing > Oppenheim and Shafer > Prentice-Hall 1975 > > Theory and Application of Digital Signal Processing > Rabiner and Gold > Prentice-Hall 1975 > > Digital Signal Processing with Kernel Method > Rojo-Alvarez et al > Wiley/IEEE 2018 > > Advanced Digital Signal Processing > and Noise Reduction > Vaseghi > Wiley 4th ed 2008 > >? Subsequent to the responses I checked: > > Spectral Analysis and Time Series > Priestly > Academic Press 1981 > > Continuous a Signals and System Analysis and Discrete > McGillem and Cooper > Holt, Reinhart and Winston 1974 > > None of them properly discuss the issue of causality. > > I did NOT look at any of the many monographs by Enders Robinson, Robinson & Treitel or John H. Karl as I know they have the matter stated very clearly. Robinson and Treitel were members of Norbert Weiner's Geophysical Analysis Group at MIT and founded the entire basis of DSP. I spent 4 years at UT Austin under another member of the GAG, Milo Backus. Robinson performed the first digital deconvolution problem in 1952 using pencil, paper and a desk calculator.? Robinson has pride of place as the first person to apply DSP to data. > > Causality requires that the real and imaginary parts be a Hilbert transform pair. This is well stated in: > > The Fourier Integral and Some of Its Applications > Ronald Bracewell > McGraw-Hill 2nd ed 1978 > > Causality simply states that there is no output prior to the input. If a filter is not causal it produces output before the event. The EE community appears to consistently label a zero phase signal as linear phase with a phase delay. As Bracewell provides a proof and I spent 2 semesters studying Churchill's "Operational Mathematics" under Bill Guy in "Integral Transforms" at Austin in addition to the semester I spent with Bracewell in "Linear Systems", if the EE community wants to redefine the math they may. I shall stick to what the mathematicians wrote. > > Have Fun! > Reg > > > > > |
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Dan, I'm not looking for simple, I'm looking for meticulously correct. I have a small book, "A Handbook of Fourier Theorems" by Champeney which I *always* consult when I am working on the fringes. This is not close to the fringes. The Fourier integral extends from -infinity to infinity. The EE delay is the result of substituting dirac(t-tau) for the correct dirac(t) when computing the impulse response. Have Fun! Reg On Saturday, July 6, 2024 at 12:03:33 PM CDT, Daniel Marks <profdc9@...> wrote: If you want something simple to implement you can use what I did in the fldigi version of SCAMP: look at the? int scamp::rx_process(const double *buf, int len) method.? It implements a simple circular buffer filter, which has a sinc-like response but its frequency may be moved around dynamically.? I use a different approach in my guitar pedal code: for example look at the "DSP_TYPE_WAH" filter effect.? This uses a dynamically changed bandpass filter based on the position of a foot pedal, and does some simple interpolation to move the center frequency around by changing the coefficients of a digital biquad filter.? All digital filters are implemented with a delay, and so none are "noncausal."? There is a compromise between group delay, which is the amount of lag that the filter applies to the signal and the sharpness of the filter.? A "minimum phase" filter minimizes this delay and has the property that the real and imaginary parts are related by the Hilbert transform.? A filter can be expressed as a cascade of a minimum phase filter and an all-pass filter. Dan On Sat, Jul 6, 2024 at 8:54?AM Reginald Beardsley via <pulaskite=yahoo.com@groups.io> wrote: I?am?working?on?numerical?modeling?of?CCW?and?am?at?the?point?that?I?need?to?write?the?code?to?implement?twin?pass?band?tuning.??As?this?is?NOT?seismic?processing?I?pulled?a?small?stack?of?my?EE?DSP?classics?and?started?reading?them. |
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At which point the oil industry had been doing digital processing of seismic data for years as we could live with 4 ms sample rates. Our peak signal was at best 30-35 Hz. Still is as the earth is the same. My introduction to seismic processing was a bunch of late '60's marine data that Amoco wanted to reprocess. The improvement in computing resources resulted in stunning improvements in the images. Those tapes also taught me a lot about cracking hex dumps of data from weird recording systems. One set of tapes was an experimental format Western Geophysical used briefly. The tip off was "ROM 14" on the observer notes. When I called Western after numerous failed demux attempts, I mentioned that. The reply was "Wait a few minutes." He came back, gave me the missing information and I was able to demux the data. Have Fun! Reg On Saturday, July 6, 2024 at 12:22:19 PM CDT, Mike Feher <n4fs@...> wrote: Most of my DSP work was in the early 70's using discrete chips. It was not even called DSP then. Built both FIT and IIR filters. At the time chips and DACs and ADCs were slow. That was OK as we were working on detecting and classifying submarine signals at acoustic frequencies. In fact, the first couple of filters that I built used serial arithmetic using chips from Rockwell Collins. Things got a lot nicer when AMD came out with parallel multipliers. All my filters were built with cascaded second order sections of the Elliptic design. Also, we used the Weaver method to make them tunable. Regards - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 908-902-3831 -----Original Message----- From: qex@groups.io <qex@groups.io> On Behalf Of Reginald Beardsley via groups.io Sent: Saturday, July 6, 2024 12:37 PM To: qex@groups.io Subject: Re: [qex] Some questions on digital filter design This is a general reply to Jeff, Mike and Dave. I initially looked at: Digital Design Handbook Fred J. Taylor Marcel Dekker 1983 Digital Signal Processing Oppenheim and Shafer Prentice-Hall 1975 Theory and Application of Digital Signal Processing Rabiner and Gold Prentice-Hall 1975 Digital Signal Processing with Kernel Method Rojo-Alvarez et al Wiley/IEEE 2018 Advanced Digital Signal Processing and Noise Reduction Vaseghi Wiley 4th ed 2008 Subsequent to the responses I checked: Spectral Analysis and Time Series Priestly Academic Press 1981 Continuous a Signals and System Analysis and Discrete McGillem and Cooper Holt, Reinhart and Winston 1974 None of them properly discuss the issue of causality. I did NOT look at any of the many monographs by Enders Robinson, Robinson & Treitel or John H. Karl as I know they have the matter stated very clearly. Robinson and Treitel were members of Norbert Weiner's Geophysical Analysis Group at MIT and founded the entire basis of DSP. I spent 4 years at UT Austin under another member of the GAG, Milo Backus. Robinson performed the first digital deconvolution problem in 1952 using pencil, paper and a desk calculator.? Robinson has pride of place as the first person to apply DSP to data. Causality requires that the real and imaginary parts be a Hilbert transform pair. This is well stated in: The Fourier Integral and Some of Its Applications Ronald Bracewell McGraw-Hill 2nd ed 1978 Causality simply states that there is no output prior to the input. If a filter is not causal it produces output before the event. The EE community appears to consistently label a zero phase signal as linear phase with a phase delay. As Bracewell provides a proof and I spent 2 semesters studying Churchill's "Operational Mathematics" under Bill Guy in "Integral Transforms" at Austin in addition to the semester I spent with Bracewell in "Linear Systems", if the EE community wants to redefine the math they may. I shall stick to what the mathematicians wrote. Have Fun! Reg |
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See my earlier comment about the definition of the Fourier transform and the impulse response. On Saturday, July 6, 2024 at 12:28:57 PM CDT, Chuck Harris <cfharris@...> wrote: Is it really a breach of causality if the output that displays the breach doesn't actually occur until some processing delay after the input that caused the output? I remember discussing this stuff at length some 50 years ago in a class on linear systems.... all I remember is discussing it, not what we decided, nor how we got there. I do recall that simplicity in the math required that certain apparently non-causal things would appear in the results. There is a whole lot of blue ink underlining way too much, in the section on convolution of the impulse function, and causality, in my copy of Linear Systems Analysis by Liu & Liu... which, for me, usually meant I was hopelessly confused... -Chuck Harris On Sat, 6 Jul 2024 16:37:12 +0000 (UTC) "Reginald Beardsley via
groups.io" <pulaskite@...> wrote: > ?This?is?a?general?reply?to?Jeff,?Mike?and?Dave.?I?initially?looked > at: > > Digital?Design?Handbook > Fred?J.?Taylor > Marcel?Dekker?1983 > > Digital?Signal?Processing > Oppenheim?and?Shafer > Prentice-Hall?1975 > > Theory?and?Application?of?Digital?Signal?Processing > Rabiner?and?Gold > Prentice-Hall?1975 > > Digital?Signal?Processing?with?Kernel?Method > Rojo-Alvarez?et?al > Wiley/IEEE?2018 > > Advanced?Digital?Signal?Processing > and?Noise?Reduction > Vaseghi > Wiley?4th?ed?2008 > > ?Subsequent?to?the?responses?I?checked: > > Spectral?Analysis?and?Time?Series > Priestly > Academic?Press?1981 > > Continuous?a?Signals?and?System?Analysis?and?Discrete > McGillem?and?Cooper > Holt,?Reinhart?and?Winston?1974 > > None?of?them?properly?discuss?the?issue?of?causality. > > I?did?NOT?look?at?any?of?the?many?monographs?by?Enders?Robinson, > Robinson?&?Treitel?or?John?H.?Karl?as?I?know?they?have?the?matter > stated?very?clearly.?Robinson?and?Treitel?were?members?of?Norbert > Weiner's?Geophysical?Analysis?Group?at?MIT?and?founded?the?entire > basis?of?DSP.?I?spent?4?years?at?UT?Austin?under?another?member?of > the?GAG,?Milo?Backus.?Robinson?performed?the?first?digital > deconvolution?problem?in?1952?using?pencil,?paper?and?a?desk > calculator.??Robinson?has?pride?of?place?as?the?first?person?to?apply > DSP?to?data. > > Causality?requires?that?the?real?and?imaginary?parts?be?a?Hilbert > transform?pair.?This?is?well?stated?in: > > The?Fourier?Integral?and?Some?of?Its?Applications > Ronald?Bracewell > McGraw-Hill?2nd?ed?1978 > > Causality?simply?states?that?there?is?no?output?prior?to?the?input. > If?a?filter?is?not?causal?it?produces?output?before?the?event.?The?EE > community?appears?to?consistently?label?a?zero?phase?signal?as?linear > phase?with?a?phase?delay.?As?Bracewell?provides?a?proof?and?I?spent?2 > semesters?studying?Churchill's?"Operational?Mathematics"?under?Bill > Guy?in?"Integral?Transforms"?at?Austin?in?addition?to?the?semester?I > spent?with?Bracewell?in?"Linear?Systems",?if?the?EE?community?wants > to?redefine?the?math?they?may.?I?shall?stick?to?what?the > mathematicians?wrote. > > Have?Fun! > Reg > > > > > |
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The book I used in school was "Analog and Digital Filters:? Design and Realization", by Harry Y-F. Lam.? The last three chapters introduce the z-transform and then discuss the design and realization of FIR and IIR digital filters based upon the z-transform. I thought it was an excellent text, but we were using it in manuscript form, pre-publishing, and in a sense we were its proof-readers. - Jeff, k6jca
On Saturday, July 6, 2024 at 10:42:12 AM PDT, Reginald Beardsley via groups.io <pulaskite@...> wrote:
Dan, I'm not looking for simple, I'm looking for meticulously correct. I have a small book, "A Handbook of Fourier Theorems" by Champeney which I *always* consult when I am working on the fringes. This is not close to the fringes. The Fourier integral extends from -infinity to infinity. The EE delay is the result of substituting dirac(t-tau) for the correct dirac(t) when computing the impulse response. Have Fun! Reg On Saturday, July 6, 2024 at 12:03:33 PM CDT, Daniel Marks <profdc9@...> wrote: If you want something simple to implement you can use what I did in the fldigi version of SCAMP: look at the? int scamp::rx_process(const double *buf, int len) method.? It implements a simple circular buffer filter, which has a sinc-like response but its frequency may be moved around dynamically.? I use a different approach in my guitar pedal code: for example look at the "DSP_TYPE_WAH" filter effect.? This uses a dynamically changed bandpass filter based on the position of a foot pedal, and does some simple interpolation to move the center frequency around by changing the coefficients of a digital biquad filter.? All digital filters are implemented with a delay, and so none are "noncausal."? There is a compromise between group delay, which is the amount of lag that the filter applies to the signal and the sharpness of the filter.? A "minimum phase" filter minimizes this delay and has the property that the real and imaginary parts are related by the Hilbert transform.? A filter can be expressed as a cascade of a minimum phase filter and an all-pass filter. Dan On Sat, Jul 6, 2024 at 8:54?AM Reginald Beardsley via <pulaskite=yahoo.com@groups.io> wrote: I?am?working?on?numerical?modeling?of?CCW?and?am?at?the?point?that?I?need?to?write?the?code?to?implement?twin?pass?band?tuning.??As?this?is?NOT?seismic?processing?I?pulled?a?small?stack?of?my?EE?DSP?classics?and?started?reading?them. |
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Daniel Marks
A lot of papers have been written and ink spilled over misapprehension as to what group delay means.? Lots of press about "signals arriving before they were sent."? They'll say anything these days to get you to click. It does not imply some magic suspension of causality.? Negative group delay only occurs for very small bandwidths, such that the impulse response width is longer in time than the negative group delay.? Certainly interesting phenomena happen in these narrow bandwidth regions (for example a negative index of refraction) but these are only time harmonic responses which take a sufficient amount of time to set up. But I think this digression into causality misses the point when discussing communication.? The time-domain signals corresponding to the symbols span a linear subspace and have distances apart (for example Euclidean or Hamming distances).? Of course these signals must be causal.? A pure sinusoidal waveform is not causal.? So if one is using a filter bank to separate frequencies, one has to decide how to handle finite-time sinusoids (for example Gaussian envelopes or cyclic prefixes). Because the signal processing computation can be a limiting factor in real-time processing, this basis is sometimes partially determine by the signals that can be more readily processed.? For example, FFT / OFDM is an example of exploiting symmetry in the filters.? Of course, with a filter bank with only a few frequencies, it might make more sense to use a small number of FIR or IIR filters. ? There's a lot that is determined by the specifics of what the goals are and what the available computational resources are.? A modern PC has an enormous amount of processing power to be used on a 2.5 kHz wide SSB signal.? Some examples of QRSS using very long convolutional codes have been able to nearly approach the limit of -1.59 dB Eb/N0. Dan On Sat, Jul 6, 2024 at 12:28?PM Chuck Harris via <cfharris=erols.com@groups.io> wrote: Is it really a breach of causality if the output |
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Reg,
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Did you do any work with Texas Instruments or their equipment? In the early 1980's one of our managers visited TI in Dallas. They showed him what he described as a "Supercomputer", using ECL logic, that was used in seismic research. Enjoy your discussions. Mike N2MS On 07/06/2024 1:51 PM EDT Reginald Beardsley via groups.io <pulaskite@...> wrote: |
开云体育I always considered Frerking to be the king of communications signal processing but the books are currently out of sight.? I realized his ALC in SHARC code and it ended up in a couple radios.? Might be available on scribd? ? Digital Signal Processing in Communications Systems https://a.co/d/03jpwjgr ? From: Chuck Harris
Sent: Saturday, July 6, 2024 10:28 AM To: qex@groups.io Subject: Re: [qex] Some questions on digital filter design ? Is it really a breach of causality if the output that displays the breach doesn't actually occur until some processing delay after the input that caused the output? ? I remember discussing this stuff at length some 50 years ago in a class on linear systems.... all I remember is discussing it, not what we decided, nor how we got there. ? I do recall that simplicity in the math required that certain apparently non-causal things would appear in the results. ? There is a whole lot of blue ink underlining way too much, in the section on convolution of the impulse function, and causality, in my copy of Linear Systems Analysis by Liu & Liu... which, for me, usually meant I was hopelessly confused... ? -Chuck Harris ? ? On Sat, 6 Jul 2024 16:37:12 +0000 (UTC) "Reginald Beardsley via groups.io" <pulaskite@...> wrote: > ?This?is?a?general?reply?to?Jeff,?Mike?and?Dave.?I?initially?looked > at: > > Digital?Design?Handbook > Fred?J.?Taylor > Marcel?Dekker?1983 > > Digital?Signal?Processing > Oppenheim?and?Shafer > Prentice-Hall?1975 > > Theory?and?Application?of?Digital?Signal?Processing > Rabiner?and?Gold > Prentice-Hall?1975 > > Digital?Signal?Processing?with?Kernel?Method > Rojo-Alvarez?et?al > Wiley/IEEE?2018 > > Advanced?Digital?Signal?Processing > and?Noise?Reduction > Vaseghi > Wiley?4th?ed?2008 > > ?Subsequent?to?the?responses?I?checked: > > Spectral?Analysis?and?Time?Series > Priestly > Academic?Press?1981 > > Continuous?a?Signals?and?System?Analysis?and?Discrete > McGillem?and?Cooper > Holt,?Reinhart?and?Winston?1974 > > None?of?them?properly?discuss?the?issue?of?causality. > > I?did?NOT?look?at?any?of?the?many?monographs?by?Enders?Robinson, > Robinson?&?Treitel?or?John?H.?Karl?as?I?know?they?have?the?matter > stated?very?clearly.?Robinson?and?Treitel?were?members?of?Norbert > Weiner's?Geophysical?Analysis?Group?at?MIT?and?founded?the?entire > basis?of?DSP.?I?spent?4?years?at?UT?Austin?under?another?member?of > the?GAG,?Milo?Backus.?Robinson?performed?the?first?digital > deconvolution?problem?in?1952?using?pencil,?paper?and?a?desk > calculator.??Robinson?has?pride?of?place?as?the?first?person?to?apply > DSP?to?data. > > Causality?requires?that?the?real?and?imaginary?parts?be?a?Hilbert > transform?pair.?This?is?well?stated?in: > > The?Fourier?Integral?and?Some?of?Its?Applications > Ronald?Bracewell > McGraw-Hill?2nd?ed?1978 > > Causality?simply?states?that?there?is?no?output?prior?to?the?input. > If?a?filter?is?not?causal?it?produces?output?before?the?event.?The?EE > community?appears?to?consistently?label?a?zero?phase?signal?as?linear > phase?with?a?phase?delay.?As?Bracewell?provides?a?proof?and?I?spent?2 > semesters?studying?Churchill's?"Operational?Mathematics"?under?Bill > Guy?in?"Integral?Transforms"?at?Austin?in?addition?to?the?semester?I > spent?with?Bracewell?in?"Linear?Systems",?if?the?EE?community?wants > to?redefine?the?math?they?may.?I?shall?stick?to?what?the > mathematicians?wrote. > > Have?Fun! > Reg > > > > > ? ? ? ? ? ? |
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FWIW I derived the reflection response for a source and receiver at arbitrary locations in plane layered media via Z transform for a class exercise. Shortly after I wrote that Treitel and Gutowski published the same thing in Geophysics. A classmate joked I should start submitting my homework to Geophysics. I really like the Z transform because the notation is so tractable. Have Fun! Reg On Saturday, July 6, 2024 at 01:49:14 PM CDT, Jeff Anderson <jca1955@...> wrote: The book I used in school was "Analog and Digital Filters:? Design and Realization", by Harry Y-F. Lam.? The last three chapters introduce the z-transform and then discuss the design and realization of FIR and IIR digital filters based upon the z-transform. I thought it was an excellent text, but we were using it in manuscript form, pre-publishing, and in a sense we were its proof-readers. - Jeff, k6jca On Saturday, July 6, 2024 at 10:42:12 AM PDT, Reginald Beardsley via groups.io <pulaskite@...> wrote: Dan, I'm not looking for simple, I'm looking for meticulously correct. I have a small book, "A Handbook of Fourier Theorems" by Champeney which I *always* consult when I am working on the fringes. This is not close to the fringes. The Fourier integral extends from -infinity to infinity. The EE delay is the result of substituting dirac(t-tau) for the correct dirac(t) when computing the impulse response. Have Fun! Reg On Saturday, July 6, 2024 at 12:03:33 PM CDT, Daniel Marks <profdc9@...> wrote: If you want something simple to implement you can use what I did in the fldigi version of SCAMP: look at the? int scamp::rx_process(const double *buf, int len) method.? It implements a simple circular buffer filter, which has a sinc-like response but its frequency may be moved around dynamically.? I use a different approach in my guitar pedal code: for example look at the "DSP_TYPE_WAH" filter effect.? This uses a dynamically changed bandpass filter based on the position of a foot pedal, and does some simple interpolation to move the center frequency around by changing the coefficients of a digital biquad filter.? All digital filters are implemented with a delay, and so none are "noncausal."? There is a compromise between group delay, which is the amount of lag that the filter applies to the signal and the sharpness of the filter.? A "minimum phase" filter minimizes this delay and has the property that the real and imaginary parts are related by the Hilbert transform.? A filter can be expressed as a cascade of a minimum phase filter and an all-pass filter. Dan On Sat, Jul 6, 2024 at 8:54?AM Reginald Beardsley via <pulaskite=yahoo.com@groups.io> wrote: I?am?working?on?numerical?modeling?of?CCW?and?am?at?the?point?that?I?need?to?write?the?code?to?implement?twin?pass?band?tuning.??As?this?is?NOT?seismic?processing?I?pulled?a?small?stack?of?my?EE?DSP?classics?and?started?reading?them. |
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It’s available on pdfcoffee. On Sat, Jul 6, 2024 at 3:21?PM Jerry via <jerry=hanler.com@groups.io> wrote:
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开云体育What is "pdfcoffee"?DaveD KC0WJN ============================== All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994) ============================== On Jul 6, 2024, at 20:09, Mark LaPlante via groups.io <mcpderez@...> wrote:
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