Bessel Filter (Digital)

Vladimir Vassilevsky <nospam@nowhere.com> wrote:
(snip)

> Everybody complains about "ringing" and overshoot, but nobody could 
> explain why it is bad.

If you burn out the output transistors, then that is bad.

I suppose that doesn't happen in theoretical problems, but it
does for real amplifiers.

-- glen

robert bristow-johnson <rbj@audioimagination.com> wrote:
(snip on overshoot)

> i can imagine a huge crane working in tight conditions and, with a 6%
> overshoot, crashes into a wall with people on the other side, bringing
> down the structure and killing dozens.  i s'pose they would blame
> Obama and i would blame Bush.

Not so far from one in Bellevue WA about four years ago.
(The newspaper article on www.seattlepi.com is dated Nov 17th, 2006.)

Only one person was killed, in the building that the crane fell on.
The crane operator was hurt, but not seriously injured.  (I believe
the operator is up on top, so that is a little surprising.)

For those who don't know Washington, it is close to Redmond, which
everyone knows about.

-- glen

Greg Berchin <gjberchin@chatter.net.invalid> wrote:
(snip on overshoot and ringing)

> Just about anything mechanical.  I had an old Ford Explorer 
> with a cruise control that overshot and rang.  Set to, for example, 
> 65 MPH; after braking hit "Resume" and it would shoot to 67 MPH, 
> then slow to 63, then continue ringing for three or four cycles 
> until it settled.  It was annoying.

(snip)

We all learn critical damping in differential equations class,
but implementing it in real systems isn't always so easy.

I usually get a little bit close before pressing "resume",
mostly to avoid the sudden acceleration that it wants to do.

-- glen

On Nov 17, 12:33=A0pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
> robert bristow-johnson wrote:
> > On Nov 17, 11:48 am, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
>
> >>>>Everybody complains about "ringing" and overshoot, but nobody could
> >>>>explain why it is bad.
>
> >>>i think the control systems people (like Tim) might be able to explain
> >>>it.
>
> >>How this is relevant to Bessel/Butterwoth/etc?
>
> > in designing your controller, you might want a net transfer function
> > (of plant with feedback and controller) that isn't a Butterworth, but
> > more like a Bessel.
>
> AFAIK they have many other criteria for loop optimization and they don't
> set matching Bessel response as the specific goal of the design.
>
> Also, as Tim said, having a Bessel filter inside a loop is not any
> condition for the whole loop to be ringing or not ringing.

it wasn't about just the controller inside, it was about the whole
thing (didn't i state it clearly?).  with enough independent
parameters of the controller ( H(s) ) to tweak, it seems possible to
me that a controller can send the poles of the whole (H*G)/(1+H*G) to
wherever you need them to be for stability and perhaps some other
design goals.  you otta be able to put the zeros wherever you wish (at
least i think you can in the digital case).

so, what else does the Bessel filter have as an interesting or
desirable quality regarding this servo-mechanism?  symmetrical edges?
does another filter have as fast step response while possessing one or
both qualities?

so then, given G, why wouldn't you try to design H so that (H*G)/
(1+H*G) is a Bessel filter or something similar (if there are other
constraints)?

r b-j

>On Nov 17, 12:33=A0pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
>> robert bristow-johnson wrote:
>> > On Nov 17, 11:48 am, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
>>
>> >>>>Everybody complains about "ringing" and overshoot, but nobody could
>> >>>>explain why it is bad.
>>
>> >>>i think the control systems people (like Tim) might be able to
explain
>> >>>it.
>>
>> >>How this is relevant to Bessel/Butterwoth/etc?
>>
>> > in designing your controller, you might want a net transfer function
>> > (of plant with feedback and controller) that isn't a Butterworth, but
>> > more like a Bessel.
>>
>> AFAIK they have many other criteria for loop optimization and they
don't
>> set matching Bessel response as the specific goal of the design.


>> Also, as Tim said, having a Bessel filter inside a loop is not any
>> condition for the whole loop to be ringing or not ringing.
>
>it wasn't about just the controller inside, it was about the whole
>thing (didn't i state it clearly?).  with enough independent
>parameters of the controller ( H(s) ) to tweak, it seems possible to
>me that a controller can send the poles of the whole (H*G)/(1+H*G) to
>wherever you need them to be for stability and perhaps some other
>design goals.  you otta be able to put the zeros wherever you wish (at
>least i think you can in the digital case).
>
>so, what else does the Bessel filter have as an interesting or
>desirable quality regarding this servo-mechanism?  symmetrical edges?
>does another filter have as fast step response while possessing one or
>both qualities?
>
>so then, given G, why wouldn't you try to design H so that (H*G)/
>(1+H*G) is a Bessel filter or something similar (if there are other
>constraints)?
>
>r b-j




I can observe that people on this forum don't give solutions to the
problems being asked. They just fight like little kids on the problem and
discuss it and try to prove that they are too smart. But actually , i sense
that they are noobs and might be possible that they copy paste the stuff
they post here . And moreover, its not a big deal to master a subject if
you are working on that subject from soo long. 

Earlier , i used this forum to ask a doubt related to FFTW and a blocking
mechanism , and that time too the condition and the responses were similar.
They never help , just wander around the topic. I am actually laughing at
this situation right now. Nevertheless, thanks guys!

Raj!

On Nov 18, 1:23=A0pm, "raj malhotra" <f2007327@n_o_s_p_a_m.bits-
goa.ac.in> wrote:

> I can observe that people on this forum don't give solutions to the
> problems being asked.

You suppose that any question deserves an answer.
Like it or not, but engineering is about progress.
The Bessel filter might have had a purpose some
time in the past, but that doesn't mean it still
has.

Once upon a time steam engines was the main technology.
These days they are mere curiosities.

Rune

>On Nov 18, 1:23=A0pm, "raj malhotra" <f2007327@n_o_s_p_a_m.bits-
>goa.ac.in> wrote:
>
>> I can observe that people on this forum don't give solutions to the
>> problems being asked.
>
>You suppose that any question deserves an answer.
>Like it or not, but engineering is about progress.
>The Bessel filter might have had a purpose some
>time in the past, but that doesn't mean it still
>has.
>
>Once upon a time steam engines was the main technology.
>These days they are mere curiosities.
>
>Rune
>

Then I'd like to know how you would design the following filter. Maybe
there are tricks I'm not aware of...

-fs = 2kHz
-fc = 40Hz
-Attenuation about 18dB/octave more or less (similar to 3rd order
Butterworth)
-maximum ringing ~1%
-low computational complexity (3 to 5 non-trivial multiplications
maximum).

Dave

raj malhotra wrote:

> I can observe that people on this forum don't give solutions to the
> problems being asked. They just fight like little kids on the problem and
> discuss it and try to prove that they are too smart.

The questions are dumb. That 2 x 2 = 4 stuff is not interesing.
If you need a solution, pay for it. Or be happy with what you are getting.

> But actually , i sense
> that they are noobs and might be possible that they copy paste the stuff
> they post here . 

:))))))) Is that what you generally do?
JFYI, this newsgroup is a place for marketing and leisure of industry 
experts.

> And moreover, its not a big deal to master a subject if
> you are working on that subject from soo long. 

Of course. Work towards your mastership.

> Earlier , i used this forum to ask a doubt related to FFTW and a blocking
> mechanism , and that time too the condition and the responses were similar.
> They never help ,

You never pay, and never will. Then what is the point of explaining the 
trivial things to you?

> just wander around the topic. I am actually laughing at
> this situation right now. Nevertheless, thanks guys!

Clever man needs just a hint; he works the details himself. You've got a 
lot of hints, still can't work the details :)))))


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

On Thu, 18 Nov 2010 09:45:48 -0600, Vladimir Vassilevsky
<nospam@nowhere.com> wrote:

>
>
>raj malhotra wrote:
>
>> I can observe that people on this forum don't give solutions to the
>> problems being asked. They just fight like little kids on the problem and
>> discuss it and try to prove that they are too smart.
>
>The questions are dumb. That 2 x 2 = 4 stuff is not interesing.
>If you need a solution, pay for it. Or be happy with what you are getting.
>
>> But actually , i sense
>> that they are noobs and might be possible that they copy paste the stuff
>> they post here . 
>
>:))))))) Is that what you generally do?
>JFYI, this newsgroup is a place for marketing and leisure of industry 
>experts.

It used to be a lot more than that.   I like to think that it still
is, or can be, but that depends entirely on the participants.  I miss
the old days.



Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com

On Nov 18, 11:42=A0am, eric.jacob...@ieee.org (Eric Jacobsen) wrote:

> ... =A0I miss the old days.

Eric, *these* are the good old days.

r b-j