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From: gretzteam on 5 Mar 2010 08:45
Hi,
I've been playing with wave lattice filters for a little while and only
yesterday realized that they were just a structure used to implement the
same good old transfer function that maps nicely onto the Direct Form I,
II, transposed etc. For some reason I thought they were a different beast.

Now I wonder how do people come up with new structures. The mapping from
the transfer function to a lattice wave filter is not obvious at all! Let's
say that I couldn't just start from DF1 and come up with a lattice
structure...

Are there still new structures being found yielding power or area
advantages?

Are there any book or research on this topic?

Thanks!
Diego
From: Rune Allnor on 5 Mar 2010 11:05
On 5 Mar, 14:45, "gretzteam" <gretzt...(a)yahoo.com> wrote:
> Hi,
> I've been playing with wave lattice filters for a little while and only
> yesterday realized that they were just a structure used to implement the
> same good old transfer function that maps nicely onto the Direct Form I,
> II, transposed etc. For some reason I thought they were a different beast.
>
> Now I wonder how do people come up with new structures. The mapping from
> the transfer function to a lattice wave filter is not obvious at all! Let's
> say that I couldn't just start from DF1 and come up with a lattice
> structure...
>
> Are there still new structures being found yielding power or area
> advantages?
>
> Are there any book or research on this topic?

There are two lines of thought on this topic:

1) There is *always* something new anexciting to be discovered.
2) Most of the useful stuff has already been discovered.

I must admit that I subscribe to view 2) - that most of the
useful DSP stuff is already ot there. This view is based on
the premise that

1) There are only so many ways to compute the same quantity
2) A lot of ridiculously smart people have reviewed the
subject in the past, which leave very little to be
discovered in the future

I know some of the regulars here disagree fiercly with me,
but it's up to them, not me, to argue in defence of their
views.

Rune
From: Jerry Avins on 5 Mar 2010 11:32
Rune Allnor wrote:
> On 5 Mar, 14:45, "gretzteam" <gretzt...(a)yahoo.com> wrote:
>> Hi,
>> I've been playing with wave lattice filters for a little while and only
>> yesterday realized that they were just a structure used to implement the
>> same good old transfer function that maps nicely onto the Direct Form I,
>> II, transposed etc. For some reason I thought they were a different beast.
>>
>> Now I wonder how do people come up with new structures. The mapping from
>> the transfer function to a lattice wave filter is not obvious at all! Let's
>> say that I couldn't just start from DF1 and come up with a lattice
>> structure...
>>
>> Are there still new structures being found yielding power or area
>> advantages?
>>
>> Are there any book or research on this topic?
>
> There are two lines of thought on this topic:
>
> 1) There is *always* something new anexciting to be discovered.
> 2) Most of the useful stuff has already been discovered.
>
> I must admit that I subscribe to view 2) - that most of the
> useful DSP stuff is already ot there. This view is based on
> the premise that
>
> 1) There are only so many ways to compute the same quantity
> 2) A lot of ridiculously smart people have reviewed the
> subject in the past, which leave very little to be
> discovered in the future
>
> I know some of the regulars here disagree fiercly with me,
> but it's up to them, not me, to argue in defence of their
> views.

Of course there are new things to be discovered. The hard question is,
are there new *useful* things to be discovered? Sometimes, a slightly
inferior solution is useful for circumventing a patent.

Jerry
--
Blaise Pascal: Men never do evil so completely and cheerfully
as when they do it from religious conviction.
��������������������������������������������������������������
From: Tim Wescott on 5 Mar 2010 11:33
Jerry Avins wrote:
> Rune Allnor wrote:
>> On 5 Mar, 14:45, "gretzteam" <gretzt...(a)yahoo.com> wrote:
>>> Hi,
>>> I've been playing with wave lattice filters for a little while and only
>>> yesterday realized that they were just a structure used to implement the
>>> same good old transfer function that maps nicely onto the Direct Form I,
>>> II, transposed etc. For some reason I thought they were a different
>>> beast.
>>>
>>> Now I wonder how do people come up with new structures. The mapping from
>>> the transfer function to a lattice wave filter is not obvious at all!
>>> Let's
>>> say that I couldn't just start from DF1 and come up with a lattice
>>> structure...
>>>
>>> Are there still new structures being found yielding power or area
>>> advantages?
>>>
>>> Are there any book or research on this topic?
>>
>> There are two lines of thought on this topic:
>>
>> 1) There is *always* something new anexciting to be discovered.
>> 2) Most of the useful stuff has already been discovered.
>>
>> I must admit that I subscribe to view 2) - that most of the
>> useful DSP stuff is already ot there. This view is based on
>> the premise that
>>
>> 1) There are only so many ways to compute the same quantity
>> 2) A lot of ridiculously smart people have reviewed the
>> subject in the past, which leave very little to be
>> discovered in the future
>>
>> I know some of the regulars here disagree fiercly with me,
>> but it's up to them, not me, to argue in defence of their
>> views.
>
> Of course there are new things to be discovered. The hard question is,
> are there new *useful* things to be discovered? Sometimes, a slightly
> inferior solution is useful for circumventing a patent.
>
> Jerry

Sometimes, an effort to circumvent a patent leads to a superior solution
(I wish I had an example to hand).

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: Tim Wescott on 5 Mar 2010 11:42
Rune Allnor wrote:
> On 5 Mar, 14:45, "gretzteam" <gretzt...(a)yahoo.com> wrote:
>> Hi,
>> I've been playing with wave lattice filters for a little while and only
>> yesterday realized that they were just a structure used to implement the
>> same good old transfer function that maps nicely onto the Direct Form I,
>> II, transposed etc. For some reason I thought they were a different beast.
>>
>> Now I wonder how do people come up with new structures. The mapping from
>> the transfer function to a lattice wave filter is not obvious at all! Let's
>> say that I couldn't just start from DF1 and come up with a lattice
>> structure...
>>
>> Are there still new structures being found yielding power or area
>> advantages?
>>
>> Are there any book or research on this topic?
>
> There are two lines of thought on this topic:
>
> 1) There is *always* something new and exciting to be discovered.
> 2) Most of the useful stuff has already been discovered.
>
> I must admit that I subscribe to view 2) - that most of the
> useful DSP stuff is already ot there. This view is based on
> the premise that
>
> 1) There are only so many ways to compute the same quantity
> 2) A lot of ridiculously smart people have reviewed the
> subject in the past, which leave very little to be
> discovered in the future
>
> I know some of the regulars here disagree fiercely with me,
> but it's up to them, not me, to argue in defense of their
> views.

I think that Rune's cynicism has a lot of evidence to back it up, but
I'm still cynical of it.

Most of the new stuff being discovered is just a variation on a theme,
and as much of it is done in pursuit of PhDs or tenure it tends to get
published with an excess of fanfare.

Having said that, I think that there is room for new techniques to be
discovered, or to be adopted by practitioners. Particularly if you're
working with an ASIC or an FPGA and you're looking to clever ways to
reduce logic and/or power I think there's room for incremental improvement.

So I don't think there are any techniques out there that are going to
offer astounding improvements, and techniques that _do_ offer
improvements are going to do so at the cost of easy understandability.
Keep in mind that the "direct form" filters have the coefficients of the
polynomials as gains -- I'm pretty sure that's why they're called
"direct form". There may be filters out there that are significantly
'better' in some technical way, but I can pretty much guarantee you that
you wouldn't be able to look at the code that generates them and just
write down the filter transfer function.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
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