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#1
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
Does there exist a dual to an AllPass, that is, a structure in which
amplitude varies with frequency, but phase does not? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#2
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On 5/18/2014 1:32 PM, Jim Thompson wrote:
Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#3
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On Sun, 18 May 2014 15:15:14 -0400, Phil Hobbs
wrote: On 5/18/2014 1:32 PM, Jim Thompson wrote: Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs I was hoping you had a change of heart ;-) (I've decided, therefore, that I've been fed some bad data from a real device :-( ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#4
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On Sun, 18 May 2014 15:15:14 -0400, Phil Hobbs wrote:
On 5/18/2014 1:32 PM, Jim Thompson wrote: Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs Couldn't you make a lowpass filter, then fix its phase shift with an all-pass? -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation |
#5
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On Sun, 18 May 2014 14:57:31 -0700, John Larkin wrote:
On Sun, 18 May 2014 15:15:14 -0400, Phil Hobbs wrote: On 5/18/2014 1:32 PM, Jim Thompson wrote: Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs Couldn't you make a lowpass filter, then fix its phase shift with an all-pass? You could make an approximation of a constant-delay filter (like Phil's symmetric FIR). But you can't keep the phase constant here in the real world. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
#6
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On 05/18/2014 05:57 PM, John Larkin wrote:
On Sun, 18 May 2014 15:15:14 -0400, Phil Hobbs wrote: On 5/18/2014 1:32 PM, Jim Thompson wrote: Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs Couldn't you make a lowpass filter, then fix its phase shift with an all-pass? You can flatten it out, or fix it in some restricted region (as in your example from last year) but you can't get rid of it everyplace. Group delay != real delay, but it's the leading order approximation. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#7
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On Mon, 19 May 2014 07:44:45 -0400, Phil Hobbs
wrote: On 05/18/2014 05:57 PM, John Larkin wrote: On Sun, 18 May 2014 15:15:14 -0400, Phil Hobbs wrote: On 5/18/2014 1:32 PM, Jim Thompson wrote: Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs Couldn't you make a lowpass filter, then fix its phase shift with an all-pass? You can flatten it out, or fix it in some restricted region (as in your example from last year) but you can't get rid of it everyplace. Group delay != real delay, but it's the leading order approximation. Cheers Phil Hobbs Jim didn't specify exactly zero phase, over an infinite frequency span; neither request would be reasonable. But it should be practical to make a lowpass filter, followed by an allpass network, that has minimal phase shift up to, say, 10 or 20x Fc. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation |
#8
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On 05/19/2014 11:29 AM, John Larkin wrote:
On Mon, 19 May 2014 07:44:45 -0400, Phil Hobbs wrote: On 05/18/2014 05:57 PM, John Larkin wrote: On Sun, 18 May 2014 15:15:14 -0400, Phil Hobbs wrote: On 5/18/2014 1:32 PM, Jim Thompson wrote: Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs Couldn't you make a lowpass filter, then fix its phase shift with an all-pass? You can flatten it out, or fix it in some restricted region (as in your example from last year) but you can't get rid of it everyplace. Group delay != real delay, but it's the leading order approximation. Cheers Phil Hobbs Jim didn't specify exactly zero phase, over an infinite frequency span; neither request would be reasonable. But it should be practical to make a lowpass filter, followed by an allpass network, that has minimal phase shift up to, say, 10 or 20x Fc. I doubt that very much. If you can do that to an LC-type lowpass, you'll put Tim Wescott and Co. out of business. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
#9
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On Mon, 19 May 2014 11:42:49 -0400, Phil Hobbs
wrote: On 05/19/2014 11:29 AM, John Larkin wrote: On Mon, 19 May 2014 07:44:45 -0400, Phil Hobbs wrote: On 05/18/2014 05:57 PM, John Larkin wrote: On Sun, 18 May 2014 15:15:14 -0400, Phil Hobbs wrote: On 5/18/2014 1:32 PM, Jim Thompson wrote: Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs Couldn't you make a lowpass filter, then fix its phase shift with an all-pass? You can flatten it out, or fix it in some restricted region (as in your example from last year) but you can't get rid of it everyplace. Group delay != real delay, but it's the leading order approximation. Cheers Phil Hobbs Jim didn't specify exactly zero phase, over an infinite frequency span; neither request would be reasonable. But it should be practical to make a lowpass filter, followed by an allpass network, that has minimal phase shift up to, say, 10 or 20x Fc. I doubt that very much. If you can do that to an LC-type lowpass, you'll put Tim Wescott and Co. out of business. Cheers Phil Hobbs I didn't say LC. I was thinking 1st order, RC, because that case is easy to think about. But it could be done to a higher-order filter, just more work. Point is, that the answer to Jim's question is that, yes, it can be done within reasonable practical limits. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation |
#10
Posted to sci.electronics.design,alt.binaries.schematics.electronic,sci.electronics.cad,sci.electronics.basics
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Dual to AllPass.?
On 05/19/2014 11:58 AM, John Larkin wrote:
On Mon, 19 May 2014 11:42:49 -0400, Phil Hobbs wrote: On 05/19/2014 11:29 AM, John Larkin wrote: On Mon, 19 May 2014 07:44:45 -0400, Phil Hobbs wrote: On 05/18/2014 05:57 PM, John Larkin wrote: On Sun, 18 May 2014 15:15:14 -0400, Phil Hobbs wrote: On 5/18/2014 1:32 PM, Jim Thompson wrote: Does there exist a dual to an AllPass, that is, a structure in which amplitude varies with frequency, but phase does not? ...Jim Thompson Wouldn't it be nice. No, in general that violates causality. (I'll be a bit less dogmatic about that than previously, since we talked about this several months back.) A symmetric FIR filter centered around t=0 might qualify, if you don't need it to be real-time. Cheers Phil Hobbs Couldn't you make a lowpass filter, then fix its phase shift with an all-pass? You can flatten it out, or fix it in some restricted region (as in your example from last year) but you can't get rid of it everyplace. Group delay != real delay, but it's the leading order approximation. Cheers Phil Hobbs Jim didn't specify exactly zero phase, over an infinite frequency span; neither request would be reasonable. But it should be practical to make a lowpass filter, followed by an allpass network, that has minimal phase shift up to, say, 10 or 20x Fc. I doubt that very much. If you can do that to an LC-type lowpass, you'll put Tim Wescott and Co. out of business. Cheers Phil Hobbs I didn't say LC. I was thinking 1st order, RC, because that case is easy to think about. But it could be done to a higher-order filter, just more work. Point is, that the answer to Jim's question is that, yes, it can be done within reasonable practical limits. First order RC filters don't have real delay--you can cancel out a lowpass with a highpass, over whatever bandwidth you like, if you can stand the loss. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
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