From: fisico32 on
Hello Forum,

I have read that in some applications a signal is distorted by an LTI
system...
To recover the original signal we could filter with inverse filter. But
this procedure would only work with minimum-phase systems...

Is that true? Why?

thanks
fisico32

From: Tim Wescott on
On 07/25/2010 02:01 PM, fisico32 wrote:
> Hello Forum,
>
> I have read that in some applications a signal is distorted by an LTI
> system...
> To recover the original signal we could filter with inverse filter. But
> this procedure would only work with minimum-phase systems...
>
> Is that true? Why?

As yourself: what filter would you need to restore a signal back to its
original form if it had been run through an LTI filter (system)?

Then ask yourself: would this filter be stable if the LTI system that
I'm correcting for isn't minimum phase?

Check back here if you can't figure out the answers.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: HardySpicer on
On Jul 26, 9:01 am, "fisico32" <marcoscipioni1(a)n_o_s_p_a_m.gmail.com>
wrote:
> Hello Forum,
>
> I have read that in some applications a signal is distorted by an LTI
> system...
> To recover the original signal we could filter with inverse filter. But
> this procedure would only work with minimum-phase systems...
>
> Is that true? Why?
>
> thanks
> fisico32

There are solutions to this problem but they involve either delays of
some sort or running the data backwards in time!


Hardy
From: fisico32 on
>On 07/25/2010 02:01 PM, fisico32 wrote:
>> Hello Forum,
>>
>> I have read that in some applications a signal is distorted by an LTI
>> system...
>> To recover the original signal we could filter with inverse filter. But
>> this procedure would only work with minimum-phase systems...
>>
>> Is that true? Why?
>
>As yourself: what filter would you need to restore a signal back to its
>original form if it had been run through an LTI filter (system)?
>
>Then ask yourself: would this filter be stable if the LTI system that
>I'm correcting for isn't minimum phase?
>
>Check back here if you can't figure out the answers.
>
>--
>
>Tim Wescott
>Wescott Design Services
>http://www.wescottdesign.com
>
>Do you need to implement control loops in software?
>"Applied Control Theory for Embedded Systems" was written for you.
>See details at http://www.wescottdesign.com/actfes/actfes.html
>

Ok, so I guess that for a stable and causal filter to have a stable and
causal inverse filter, the filter can only be minimum phase.
So, in real life all filters must be minimum phase?

Surely we could have a causal and stable filter whose inverse is not stable
and causal, correct?

From: Tim Wescott on
On 07/27/2010 07:09 PM, fisico32 wrote:
>> On 07/25/2010 02:01 PM, fisico32 wrote:
>>> Hello Forum,
>>>
>>> I have read that in some applications a signal is distorted by an LTI
>>> system...
>>> To recover the original signal we could filter with inverse filter. But
>>> this procedure would only work with minimum-phase systems...
>>>
>>> Is that true? Why?
>>
>> As yourself: what filter would you need to restore a signal back to its
>> original form if it had been run through an LTI filter (system)?
>>
>> Then ask yourself: would this filter be stable if the LTI system that
>> I'm correcting for isn't minimum phase?
>>
>> Check back here if you can't figure out the answers.
>>
>> --
>>
>> Tim Wescott
>> Wescott Design Services
>> http://www.wescottdesign.com
>>
>> Do you need to implement control loops in software?
>> "Applied Control Theory for Embedded Systems" was written for you.
>> See details at http://www.wescottdesign.com/actfes/actfes.html
>>
>
> Ok, so I guess that for a stable and causal filter to have a stable and
> causal inverse filter, the filter can only be minimum phase.
> So, in real life all filters must be minimum phase?
>
> Surely we could have a causal and stable filter whose inverse is not stable
> and causal, correct?
>
Google "all pass filter".

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html