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From: Jerry Avins on 1 Feb 2010 06:30
Rune Allnor wrote:
> On 1 Feb, 00:52, Jerry Avins <j...(a)ieee.org> wrote:
>
>> We speak different languages. On this side of the Atlantic, Butterworth
>> means maximally flat,
> ...
>> Because A(f) falls monotonically as f
>> increases, there is no ripple. There are many filters with no ripple,
>> but only the Butterworth is maximally flat in the sense I defined above.
>
> I think the problem is the definition of the term 'ripple'.
>
> If one interprets it literally, as something like 'fluctuating
> back and forth', then yes, the Butterworth has no ripple.
>
> If, on the other hand, one interprets the term as 'deviation
> from desired value', then it is immediately clear that the
> Butterworth lowpass filter has a non-zero ripple everywhere
> except at DC.

It does the art no good to misapply a term that should be clear to all.
If "ripple" comes to mean "deviation from desired value", then nearly
every filter and constructed transfer function will display ripple. If
we allow that use, "ripple" loses its meaning and we shall have to
invent another term. "Actual ripple", perhaps?

> I wasn't there to see what actually happened, but I wouldn't be
> surprised if the term 'ripple' was preferred over 'deviations
> from desired value' for rather pragmatic reasons...

There's a lot of sloppy language in use, most of it used casually and
forgotten. We will lose the ability to communicate if we adopt every
illogical neologism.

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
From: Jerry Avins on 1 Feb 2010 06:28
Rune Allnor wrote:
> On 1 Feb, 00:52, Jerry Avins <j...(a)ieee.org> wrote:
>
>> We speak different languages. On this side of the Atlantic, Butterworth
>> means maximally flat,
> ...
>> Because A(f) falls monotonically as f
>> increases, there is no ripple. There are many filters with no ripple,
>> but only the Butterworth is maximally flat in the sense I defined above.
>
> I think the problem is the definition of the term 'ripple'.
>
> If one interprets it literally, as something like 'fluctuating
> back and forth', then yes, the Butterworth has no ripple.
>
> If, on the other hand, one interprets the term as 'deviation
> from desired value', then it is immediately clear that the
> Butterworth lowpass filter has a non-zero ripple everywhere
> except at DC.

It does the art no good to misapply a term that should be clear to all.
If "ripple" comes to mean "deviation from desired value", then nearly
every filter and constructed transfer function will display ripple. If
we allow that use, "ripple" loses its meaning and we shall have to
invent another term. "Actual ripple", perhaps?

> I wasn't there to see what actually happened, but I wouldn't be
> surprised if the term 'ripple' was preferred over 'deviations
> from desired value' for rather pragmatic reasons...

There's a lot of sloppy language in use, most of it used casually and
forgotten. We will lose the ability to communicate if we adopt every
illogical neologism.

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