First order Peaking Filter

[Chris Barrett]

Andor wrote:
> On 26 Jul., 15:17, Jerry Avins <[email protected]> wrote:
>
>>mtbalu wrote:
>>
>>>Hi,
>>
>>>I'm designing a peaking filter.
>>>I used RBJ Audio-EQ-Cookbook to design it in second- order and it's
>>>working fine..
>>
>>Good.
>>
>>
>>>But now i want to combine two such filters, which is making it to be
>>>fourth order which i cant afford in the current project..
>>
>>Combine how? simply cascading two filters doesn't change the order of
>>either.
>
>
> But it adds up to a system of fourth order. Obviously, Bala needs two
> humps but only has computational power for a first order system.
> Sounds like tough luck to me.
>
> Regards,
> Andor
>

Couldn't he just make a two-pole filter that is second order?

[mtbalu]

Hi,

I'm designing a peaking filter.
I used RBJ Audio-EQ-Cookbook to design it in second- order and it'
working fine..
But now i want to combine two such filters, which is making it to b
fourth order which i cant afford in the current project..

If somebody knows the coefficients for a first-order peaking filter
please post it.

Or any other idea to make peaking at two different frequencies using
second order filter would also be very useful.

Thanks,
Bala

[Jerry Avins]

mtbalu wrote:
> Hi,
>
> I'm designing a peaking filter.
> I used RBJ Audio-EQ-Cookbook to design it in second- order and it's
> working fine..

Good.

> But now i want to combine two such filters, which is making it to be
> fourth order which i cant afford in the current project..

Combine how? simply cascading two filters doesn't change the order of
either.

> If somebody knows the coefficients for a first-order peaking filter,
> please post it.

There can be no first-order peaking filter. Resonance or it's equivalent
requires complex-conjugate poles.

> Or any other idea to make peaking at two different frequencies using a
> second order filter would also be very useful.

Cascade?

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

[Andor]

On 26 Jul., 15:17, Jerry Avins <[email protected]> wrote:
> mtbalu wrote:
> > Hi,
>
> > I'm designing a peaking filter.
> > I used RBJ Audio-EQ-Cookbook to design it in second- order and it's
> > working fine..
>
> Good.
>
> > But now i want to combine two such filters, which is making it to be
> > fourth order which i cant afford in the current project..
>
> Combine how? simply cascading two filters doesn't change the order of
> either.

But it adds up to a system of fourth order. Obviously, Bala needs two
humps but only has computational power for a first order system.
Sounds like tough luck to me.

Regards,
Andor

[Tim Wescott]

On Thu, 26 Jul 2007 07:49:11 -0700, Andor wrote:

> On 26 Jul., 15:17, Jerry Avins <[email protected]> wrote:
>> mtbalu wrote:
>> > Hi,
>>
>> > I'm designing a peaking filter.
>> > I used RBJ Audio-EQ-Cookbook to design it in second- order and it's
>> > working fine..
>>
>> Good.
>>
>> > But now i want to combine two such filters, which is making it to be
>> > fourth order which i cant afford in the current project..
>>
>> Combine how? simply cascading two filters doesn't change the order of
>> either.
>
> But it adds up to a system of fourth order. Obviously, Bala needs two
> humps but only has computational power for a first order system.
> Sounds like tough luck to me.
>
If that's truly the case then yes, tough luck. He should ponder on
whether he can do the computation faster, by using assembly, or ditching
floating point in favor of integer calculations, or by using integer data
and shifts instead of multiplies. There may be routes to getting what he
needs with what he has.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

[Jerry Avins]

Chris Barrett wrote:
> Andor wrote:
>> On 26 Jul., 15:17, Jerry Avins <[email protected]> wrote:
>>
>>> mtbalu wrote:
>>>
>>>> Hi,
>>>
>>>> I'm designing a peaking filter.
>>>> I used RBJ Audio-EQ-Cookbook to design it in second- order and it's
>>>> working fine..
>>>
>>> Good.
>>>
>>>
>>>> But now i want to combine two such filters, which is making it to be
>>>> fourth order which i cant afford in the current project..
>>>
>>> Combine how? simply cascading two filters doesn't change the order of
>>> either.
>>
>>
>> But it adds up to a system of fourth order. Obviously, Bala needs two
>> humps but only has computational power for a first order system.
>> Sounds like tough luck to me.
>>
>> Regards,
>> Andor
>>
>
> Couldn't he just make a two-pole filter that is second order?

Yes, but not with two independently placed peaks.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

[Jerry Avins]

Andor wrote:
> On 26 Jul., 15:17, Jerry Avins <[email protected]> wrote:
>> mtbalu wrote:
>>> Hi,
>>> I'm designing a peaking filter.
>>> I used RBJ Audio-EQ-Cookbook to design it in second- order and it's
>>> working fine..
>> Good.
>>
>>> But now i want to combine two such filters, which is making it to be
>>> fourth order which i cant afford in the current project..
>> Combine how? simply cascading two filters doesn't change the order of
>> either.
>
> But it adds up to a system of fourth order. Obviously, Bala needs two
> humps but only has computational power for a first order system.
> Sounds like tough luck to me.

Andor

If he can't add another filter of the type he already had working, he'll
probably run out of cycles before he finishes his task anyway. I'm
guessing that he thinks 4th order is a big deal (it can be) and didn't
realize that two second-order filters can do his job.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

[Tim Wescott]

Chris Barrett wrote:
> Andor wrote:
>> On 26 Jul., 15:17, Jerry Avins <[email protected]> wrote:
>>
>>> mtbalu wrote:
>>>
>>>> Hi,
>>>
>>>> I'm designing a peaking filter.
>>>> I used RBJ Audio-EQ-Cookbook to design it in second- order and it's
>>>> working fine..
>>>
>>> Good.
>>>
>>>
>>>> But now i want to combine two such filters, which is making it to be
>>>> fourth order which i cant afford in the current project..
>>>
>>> Combine how? simply cascading two filters doesn't change the order of
>>> either.
>>
>>
>> But it adds up to a system of fourth order. Obviously, Bala needs two
>> humps but only has computational power for a first order system.
>> Sounds like tough luck to me.
>>
>> Regards,
>> Andor
>>
>
> Couldn't he just make a two-pole filter that is second order?

All two-pole filters are second order. The order count is the pole count.

One second-order filter will make one peak at some non-zero frequency.
If you need two peaks, you need two filters.

--

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

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

[Andor]

On 26 Jul., 21:12, Jerry Avins <[email protected]> wrote:
> Chris Barrett wrote:
> > Andor wrote:
> >> On 26 Jul., 15:17, Jerry Avins <[email protected]> wrote:
>
> >>> mtbalu wrote:
>
> >>>> Hi,
>
> >>>> I'm designing a peaking filter.
> >>>> I used RBJ Audio-EQ-Cookbook to design it in second- order and it's
> >>>> working fine..
>
> >>> Good.
>
> >>>> But now i want to combine two such filters, which is making it to be
> >>>> fourth order which i cant afford in the current project..
>
> >>> Combine how? simply cascading two filters doesn't change the order of
> >>> either.
>
> >> But it adds up to a system of fourth order. Obviously, Bala needs two
> >> humps but only has computational power for a first order system.
> >> Sounds like tough luck to me.
>
> >> Regards,
> >> Andor
>
> > Couldn't he just make a two-pole filter that is second order?
>
> Yes, but not with two independently placed peaks.

You can place the poles wherever you want. Complex filter output might
pose a problem, though :-).

[Vladimir Vassilevsky]

Tim Wescott wrote:


>
> All two-pole filters are second order. The order count is the pole count.
>
> One second-order filter will make one peak at some non-zero frequency.
> If you need two peaks, you need two filters.

The order of filter and the required number of taps are not the same
things. There are comb filters. Rather peculiar responses can be made by
the smart manipulation of gains and delays in the feedback and
feedforward paths. It can be more efficient then the classic approach.


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com