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Discussion Groups | Comp.DSP | fir decimation filters

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fir decimation filters - saras - 2005-11-23 00:35:00

hi..

I wnat to design a fir decimation filter with 32 taps , input width 16,
coefff width 16 .plz give me suggestions to implement this.


Re: fir decimation filters - Bhaskar Thiagarajan - 2005-11-23 12:13:00

"saras" <s...@yahoo.co.in> wrote in message
news:1...@z14g2000cwz.googlegroups.com...
> hi..
>
> I wnat to design a fir decimation filter with 32 taps , input width 16,
> coefff width 16 .plz give me suggestions to implement this.

Implement this on what?
What are your filter and decimation requirements?

Cheers
Bhaskar


Re: fir decimation filters - Jerry Avins - 2005-11-23 12:39:00

Bhaskar Thiagarajan wrote:
> "saras" <s...@yahoo.co.in> wrote in message
> news:1...@z14g2000cwz.googlegroups.com...
> 
>>hi..
>>
>>I wnat to design a fir decimation filter with 32 taps , input width 16,
>>coefff width 16 .plz give me suggestions to implement this.
> 
> 
> Implement this on what?
> What are your filter and decimation requirements?
> 
> Cheers
> Bhaskar

Once, as a summer intern, I was asked to make a breadboarding mock-up. I 
made a few chassis in different standard sizes out of expanded material 
(like flattened wire lath) instead of solid steel, so one could see 
through them. I took the iron cores out of a few sizes of transformers 
and replaced them with light spacers, then fastened magnets to them. I 
sawed the pins of tubes of various sizes and embedded magnets in the 
bases. So on for other parts: resistors in different wattages, 
capacitors in different types, "birdies" (tie points), potentiometers 
without shafts, knobs, and more.

I went to the stockroom with a list of the items I wanted, identified by 
size but not value. A asked the clerk to give me the least expensive 
parts that met my needs. He said that he needed specific part numbers, 
so I asked him for a price list that would let me choose wisely.

At that point, he lost his cool. "What are you building anyway? How can 
you make something work without the right components?" His sneer bugged 
me, and I answered, "If the circuit is really good, the actual component 
values don't matter." We must have had an audience. My mock-up set was 
both praised and well used, but people all around the plant quoted "If 
the circuit is really good, the actual components don't matter" at every 
excuse.

If the decimation filter is designed right, the actual requirements 
don't matter.

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


Re: fir decimation filters - Bhaskar Thiagarajan - 2005-11-23 13:33:00

"Jerry Avins" <j...@ieee.org> wrote in message
news:U...@rcn.net...
> Bhaskar Thiagarajan wrote:
> > "saras" <s...@yahoo.co.in> wrote in message
> > news:1...@z14g2000cwz.googlegroups.com...
> >
> >>hi..
> >>
> >>I wnat to design a fir decimation filter with 32 taps , input width 16,
> >>coefff width 16 .plz give me suggestions to implement this.
> >
> >
> > Implement this on what?
> > What are your filter and decimation requirements?
> >
> > Cheers
> > Bhaskar
>
> Once, as a summer intern, I was asked to make a breadboarding mock-up. I
> made a few chassis in different standard sizes out of expanded material
> (like flattened wire lath) instead of solid steel, so one could see
> through them. I took the iron cores out of a few sizes of transformers
> and replaced them with light spacers, then fastened magnets to them. I
> sawed the pins of tubes of various sizes and embedded magnets in the
> bases. So on for other parts: resistors in different wattages,
> capacitors in different types, "birdies" (tie points), potentiometers
> without shafts, knobs, and more.
>
> I went to the stockroom with a list of the items I wanted, identified by
> size but not value. A asked the clerk to give me the least expensive
> parts that met my needs. He said that he needed specific part numbers,
> so I asked him for a price list that would let me choose wisely.
>
> At that point, he lost his cool. "What are you building anyway? How can
> you make something work without the right components?" His sneer bugged
> me, and I answered, "If the circuit is really good, the actual component
> values don't matter." We must have had an audience. My mock-up set was
> both praised and well used, but people all around the plant quoted "If
> the circuit is really good, the actual components don't matter" at every
> excuse.
>
> If the decimation filter is designed right, the actual requirements
> don't matter.

I like your story and punch line !!
If I don't know what is 'right' I can't design it. I'm sure you get it but I
want the OP to get it too. At a minimum one needs to know what the
decimation ratio needs to be before designing the filter...I'll agree with
your final statement once this is known.

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


Re: fir decimation filters - saras - 2005-11-24 02:11:00

hi all..
thanks for reply!!

now, the specifications are decimation ratio =2, taps2, input and
coeff width . I want an idea about the filter stuctures  to be used
,so that the no of multiplications can be reduced.


Re: fir decimation filters - saras - 2005-11-25 04:51:00

hi..
any help????????????


Re: fir decimation filters - Andor - 2005-11-26 12:27:00

saras wrote:

> now, the specifications are decimation ratio =2, taps2, input and
> coeff width .

A minimax halfband filter might be a good compromise. Our very own Fred
Marshall has written a free program that computes such coefficients:

ftp://ftp.mission-systems-inc.com/outgoing/Halfband/

I'm not sure whether Meteor can beat this, you might want to have a try
as well:

http://www.cs.princeton.edu/~ken/meteor.html

As far as I remember, at an equal number of taps you can achieve even
better magnitude performance when you drop the linear-phase
requirement, but I don't know any programs to design such FIRs.
Anybody?

Other trade-offs in your design are bandwidth versus stopband
attenuation. Since you haven't posted any requirements or optimality
criteria, it's futile to be more specific.

Regards,
Andor


Re: fir decimation filters - Andor - 2005-11-26 12:27:00

saras wrote:

> now, the specifications are decimation ratio =2, taps2, input and
> coeff width .

A minimax halfband filter might be a good compromise. Our very own Fred
Marshall has written a free program that computes such coefficients:

ftp://ftp.mission-systems-inc.com/outgoing/Halfband/

I'm not sure whether Meteor can beat this, you might want to have a try
as well:

http://www.cs.princeton.edu/~ken/meteor.html

As far as I remember, at an equal number of taps you can achieve even
better magnitude performance when you drop the linear-phase
requirement, but I don't know any programs to design such FIRs.
Anybody?

Other trade-offs in your design are bandwidth versus stopband
attenuation. Since you haven't posted any requirements or optimality
criteria, it's futile to be more specific.

Regards,
Andor