Digital filter simulators?
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Digital filter simulators?
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Joerg
Guest
Posted: Mon Dec 19, 2005 1:15 am    Post subject: Digital filter simulators? Reply with quote
Hello Folks,

Is there a low/no cost simulator tool for non-ideal digital filters,
maybe from a university?

What I want to do is briefly simulate the effects of reduced coefficient
granularity in filters such as WDF. IOW, play around a bit. I know I
could do this with Matlab but that is an expensive piece of software
that I wouldn't really need for anything else. Writing code for the PC
or writing a huge spreadsheet routine is another option but takes too
long. I am looking for something equivalent to what SPICE is for the
analog world. Ideally where you could use test tapes piped in through
the sound card.

I have some filter design software that came with DSP books but they
don't go that far. They assume 'ideal' coefficient granularity base on
the available word width. Didn't find anything with Google but maybe I
hadn't used optimal search phrases.

Regards, Joerg

http://www.analogconsultants.com
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Tim Wescott
Guest
Posted: Mon Dec 19, 2005 1:15 am    Post subject: Re: Digital filter simulators? Reply with quote
Joerg wrote:

Quote:
Hello Folks,

Is there a low/no cost simulator tool for non-ideal digital filters,
maybe from a university?

What I want to do is briefly simulate the effects of reduced coefficient
granularity in filters such as WDF. IOW, play around a bit. I know I
could do this with Matlab but that is an expensive piece of software
that I wouldn't really need for anything else. Writing code for the PC
or writing a huge spreadsheet routine is another option but takes too
long. I am looking for something equivalent to what SPICE is for the
analog world. Ideally where you could use test tapes piped in through
the sound card.

I have some filter design software that came with DSP books but they
don't go that far. They assume 'ideal' coefficient granularity base on
the available word width. Didn't find anything with Google but maybe I
hadn't used optimal search phrases.

Regards, Joerg

http://www.analogconsultants.com

SciLab (http://www.scilab.com). The last time I recommended it the
fellow responded with "boy, it's about as user friendly as a chainsaw".
I had to disagree because chainsaws come with instruction manuals and
finger guards.

But it's as powerful as MatLab, it's very MatLab-like in the way it
works (although the details are quite different), it's free, it's being
maintained, and it has good newsgroup support (on
comp.soft-sys.math.scilab). I find that for control systems work its
better than Matlab because it comes with a native type for polynomial
ratios that gives you transfer functions in s and z, and another one for
representing state-space systems.

For your stuff you can use the z-domain transfer functions and force
granularity on the coefficients. If you need to investigate fixed-point
arithmetic it has a discrete-time ODE solver that works well.

You may also want to look into Octave, which is also free but apparently
no longer well maintained. I keep it around because its nearly 100%
MatLab compatible, but the version that comes with Cygwin doesn't really
work right and the Cygwin-independent version doesn't play well with Cygwin.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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Vladimir Vassilevsky
Guest
Posted: Mon Dec 19, 2005 1:15 am    Post subject: Re: Digital filter simulators? Reply with quote
Joerg wrote:

Quote:
Hello Folks,

Is there a low/no cost simulator tool for non-ideal digital filters,
maybe from a university?

What I want to do is briefly simulate the effects of reduced coefficient
granularity in filters such as WDF. IOW, play around a bit. I know I
could do this with Matlab but that is an expensive piece of software
that I wouldn't really need for anything else. Writing code for the PC
or writing a huge spreadsheet routine is another option but takes too
long. I am looking for something equivalent to what SPICE is for the
analog world. Ideally where you could use test tapes piped in through
the sound card.

I have some filter design software that came with DSP books but they
don't go that far. They assume 'ideal' coefficient granularity base on
the available word width. Didn't find anything with Google but maybe I
hadn't used optimal search phrases.


Joerg,

The good book where you can find the treatment of the digital filter
limited precision artifacts is:

Dietrich Schlichtharle. Digital Filters: Basics and Design.
Springer ISBN 3-540-66841-1

In most cases the analysis is not very complicated; there is really no
point to do the simulation.


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com
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John Herman
Guest
Posted: Mon Dec 19, 2005 7:17 am    Post subject: Re: Digital filter simulators? Reply with quote
There is also Ptolomey. It's free but it may be more than you want. I
haven't used it.



In article <stydnUmu99f5dDjeRVn-gw@web-ster.com>, Tim Wescott
<tim@seemywebsite.com> wrote:
Quote:
Joerg wrote:

Hello Folks,

Is there a low/no cost simulator tool for non-ideal digital filters,
maybe from a university?

What I want to do is briefly simulate the effects of reduced coefficient
granularity in filters such as WDF. IOW, play around a bit. I know I
could do this with Matlab but that is an expensive piece of software
that I wouldn't really need for anything else. Writing code for the PC
or writing a huge spreadsheet routine is another option but takes too
long. I am looking for something equivalent to what SPICE is for the
analog world. Ideally where you could use test tapes piped in through
the sound card.

I have some filter design software that came with DSP books but they
don't go that far. They assume 'ideal' coefficient granularity base on
the available word width. Didn't find anything with Google but maybe I
hadn't used optimal search phrases.

Regards, Joerg

http://www.analogconsultants.com

SciLab (http://www.scilab.com). The last time I recommended it the
fellow responded with "boy, it's about as user friendly as a chainsaw".
I had to disagree because chainsaws come with instruction manuals and
finger guards.

But it's as powerful as MatLab, it's very MatLab-like in the way it
works (although the details are quite different), it's free, it's being
maintained, and it has good newsgroup support (on
comp.soft-sys.math.scilab). I find that for control systems work its
better than Matlab because it comes with a native type for polynomial
ratios that gives you transfer functions in s and z, and another one for
representing state-space systems.

For your stuff you can use the z-domain transfer functions and force
granularity on the coefficients. If you need to investigate fixed-point
arithmetic it has a discrete-time ODE solver that works well.

You may also want to look into Octave, which is also free but apparently
no longer well maintained. I keep it around because its nearly 100%
MatLab compatible, but the version that comes with Cygwin doesn't really
work right and the Cygwin-independent version doesn't play well with Cygwin.
Back to top
Joerg
Guest
Posted: Mon Dec 19, 2005 7:49 am    Post subject: Re: Digital filter simulators? Reply with quote
Hello Tim,

Quote:
SciLab (http://www.scilab.com). The last time I recommended it the
fellow responded with "boy, it's about as user friendly as a chainsaw".
I had to disagree because chainsaws come with instruction manuals and
finger guards.


Thank you, I will try that out. If it's like a chainsaw I'll be comfy.
The only somewhat tricky task with chainsaws is the correct sharpening
of the chain when the fingers are almost frozen. Also, I don't trust
those 'automatic' oilers anymore and always carry a pot of chain oil
with me.

Just in case others are also interested, it's: http://www.scilab.org

Regards, Joerg

http://www.analogconsultants.com
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Joerg
Guest
Posted: Mon Dec 19, 2005 8:11 am    Post subject: Re: Digital filter simulators? Reply with quote
Hello Vladimir,

Quote:
The good book where you can find the treatment of the digital filter
limited precision artifacts is:

Dietrich Schlichtharle. Digital Filters: Basics and Design.
Springer ISBN 3-540-66841-1


Thanks. I'll play around with Scilab and when that doesn't get me going
I'll order the book. Luckily it is still available on Amazon, about $90.
I was kind of surprised that IEEE doesn't carry it.


Quote:
In most cases the analysis is not very complicated; there is really no
point to do the simulation.


I'll have to try it out somehow by piping in real test data and see what
the noise levels will be. IOW how much of unwanted response each filter
produces. It is hard to forecast that when things in the signal path can
go non-linear as in my case.

Regards, Joerg

http://www.analogconsultants.com
Back to top
Joerg
Guest
Posted: Mon Dec 19, 2005 9:15 am    Post subject: Re: Digital filter simulators? Reply with quote
Hello Jerry,
Quote:

Octave. Scilab. Any program that plots filters with coefficients you
give it -- modify ideal filters to suit your test.


After Tim mentioned Scilab I played with it a bit. Looks like quite a
learning curve so maybe I just fire up the solder iron, get a 16bit ADC
plus a good uC and try all this out in the lab.

Problem is, the lab is also where the Christmas cookie jar is and I
can't stay away from it.

Tim: Scilab is more complicated than a chainsaw, at least for a hardware
guy...

Regards, Joerg

http://www.analogconsultants.com
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Jerry Avins
Guest
Posted: Mon Dec 19, 2005 9:15 am    Post subject: Re: Digital filter simulators? Reply with quote
Joerg wrote:
Quote:
Hello Folks,

Is there a low/no cost simulator tool for non-ideal digital filters,
maybe from a university?

What I want to do is briefly simulate the effects of reduced coefficient
granularity in filters such as WDF. IOW, play around a bit. I know I
could do this with Matlab but that is an expensive piece of software
that I wouldn't really need for anything else. Writing code for the PC
or writing a huge spreadsheet routine is another option but takes too
long. I am looking for something equivalent to what SPICE is for the
analog world. Ideally where you could use test tapes piped in through
the sound card.

I have some filter design software that came with DSP books but they
don't go that far. They assume 'ideal' coefficient granularity base on
the available word width. Didn't find anything with Google but maybe I
hadn't used optimal search phrases.

Octave. Scilab. Any program that plots filters with coefficients you
give it -- modify ideal filters to suit your test.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
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Tim Wescott
Guest
Posted: Mon Dec 19, 2005 5:16 pm    Post subject: Re: Digital filter simulators? Reply with quote
Joerg wrote:
-snip-

Quote:

Just in case others are also interested, it's: http://www.scilab.org

Regards, Joerg

http://www.analogconsultants.com

Oops.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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Tim Wescott
Guest
Posted: Mon Dec 19, 2005 11:37 pm    Post subject: Re: Digital filter simulators? Reply with quote
Joerg wrote:

Quote:
Hello Vladimir,

The good book where you can find the treatment of the digital filter
limited precision artifacts is:

Dietrich Schlichtharle. Digital Filters: Basics and Design.
Springer ISBN 3-540-66841-1


Thanks. I'll play around with Scilab and when that doesn't get me going
I'll order the book. Luckily it is still available on Amazon, about $90.
I was kind of surprised that IEEE doesn't carry it.


In most cases the analysis is not very complicated; there is really no
point to do the simulation.


I'll have to try it out somehow by piping in real test data and see what
the noise levels will be. IOW how much of unwanted response each filter
produces. It is hard to forecast that when things in the signal path can
go non-linear as in my case.

Regards, Joerg

http://www.analogconsultants.com

If you think that Scilab has a future with you get a copy of
"Engineering and Scientific Computing with Scilab with CDROM"
by Claude Gomez. Neither it nor the Scilab on-line documentation give
you the complete picture, and even with both there are still holes, but
it'll give you a good step up. I found it particularly helpful with
making decent graphs.

If someone would fund me, and if I thought the Scilab team would pay
attention, I'd love to dig in and write _good_ documentation for that
package.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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sivakanth.telasula@gmail.
Guest
Posted: Tue Dec 20, 2005 1:01 am    Post subject: Re: Digital filter simulators? Reply with quote
Try Octave! The syntax is very much similar to MATLAB
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Tim Wescott
Guest
Posted: Tue Dec 20, 2005 1:16 am    Post subject: Re: Digital filter simulators? Reply with quote
Rune Allnor wrote:

Quote:
Joerg wrote:

I have some filter design software that came with DSP books but they
don't go that far. They assume 'ideal' coefficient granularity base on
the available word width. Didn't find anything with Google but maybe I
hadn't used optimal search phrases.


Out of curiosity: What is "coefficient granularity"?
Never heard the term before.

Rune

Jeorg: You mean quantization, right?


You shouldn't overlook data quantization, either. Both coefficient and
data quantization can be easily modeled and analyzed without having to
simulate, although its usually a good idea to simulate so you'll find
out what you forgot to account for.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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Joerg
Guest
Posted: Tue Dec 20, 2005 1:16 am    Post subject: Re: Digital filter simulators? Reply with quote
Hello Rune,
Quote:

Out of curiosity: What is "coefficient granularity"?
Never heard the term before.


The reduction of the total available number of coefficients to less than
the word width would theoretically allow. IOW causing the selection to
be more granular than usual.

For example let's say a certain project cannot afford a device with a HW
multiplier and must also run on batteries, limiting the processor clock
frequency. To save on processor cycles the amount of ones in an eight
bit data word that is to be used as a multiplier may have to be limited
to, say, four or five.

Granularity is probably not a common word in the DSP world. It is often
used in radar and ultrasound beamforming which is my home turf.

Regards, Joerg

http://www.analogconsultants.com
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Joerg
Guest
Posted: Tue Dec 20, 2005 1:16 am    Post subject: Re: Digital filter simulators? Reply with quote
Hello Tim,

Quote:
Jeorg: You mean quantization, right?


Kind of. It's like picking the low hanging fruit, coefficients that have
the least number of ones in there. I have pretty much given up on the
luxury of a HW multiplier for the project at hand (or the proposal
thereof). Too expensive.


Quote:
You shouldn't overlook data quantization, either. Both coefficient and
data quantization can be easily modeled and analyzed without having to
simulate, although its usually a good idea to simulate so you'll find
out what you forgot to account for.


True. In my case it might not easily work though because I have to
filter first and then 'level select'. I need a huge dynamic range.
Ranging before the filters would cost too much precious horsepower and
RAM. So data will be 16 bits while the coefficients are probably going
to have to be 6-8 bits.

Regards, Joerg

http://www.analogconsultants.com
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Tim Wescott
Guest
Posted: Tue Dec 20, 2005 1:16 am    Post subject: Re: Digital filter simulators? Reply with quote
Joerg wrote:

Quote:
Hello Rune,


Out of curiosity: What is "coefficient granularity"?
Never heard the term before.


The reduction of the total available number of coefficients to less than
the word width would theoretically allow. IOW causing the selection to
be more granular than usual.

For example let's say a certain project cannot afford a device with a HW
multiplier and must also run on batteries, limiting the processor clock
frequency. To save on processor cycles the amount of ones in an eight
bit data word that is to be used as a multiplier may have to be limited
to, say, four or five.

Granularity is probably not a common word in the DSP world. It is often
used in radar and ultrasound beamforming which is my home turf.

Regards, Joerg

http://www.analogconsultants.com

You should stick to "quantization" if you want us poor DSP types to
understand.

Restricting the precision of the multiplication to save time works for me.

--

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