Eric Jacobsen <eric.jacobsen@[EMAIL PROTECTED]
> writes:
> On Fri, 10 Oct 2008 11:54:52 -0500, Richard Owlett
> <rowlett@[EMAIL PROTECTED]
> wrote:
>
>>julius wrote:
>>> On Oct 9, 9:02 pm, Richard Owlett <rowl...@[EMAIL PROTECTED]
> wrote:
>>>
>>>>I'm interested in Magnitude vs Frequency.
>>>>I have a strictly Real input sequence.
>>>>There's Fast Hartley transform code available for my preferred
language.
>>>>Relative speed is not an issue as I'm working on stored data.
>>>>
>>>>What gotcha's should I watch out for?
>>>>Is the a good comparison on the web of their practical differences?
>>>>
>>>>TIA
>>>
>>>
>>> Richard, maybe it's better if you tell us what your intended
>>> application
>>> is. Right now it sounds a bit like asking whether you should buy a
>>> sedan
>>> or a hatchback :-P. There will be lots of opinions, but they are
>>> worthless
>>> depending on your situation and application.
>>
>>Well, my app is about as simple as it gets.
>>I have a time sequence f(t) and I want a measure of abs(f(omega))
>>Signal so far has been audio, but don't think that bears on question.
>>I'm not going to filter/process/... the transformed data, just plot it.
>>I have been using an FFT so far.
>>I wish to change hardware/OS/etc.
>>There is existing FHT code that I can cut and paste.
>>Wikipedia article seemed to imply FHT lost favor to FFT when faster FFT
>>algorithms were developed.
>
> Back when processing power and memory were hard to come by I used to
> use FHTs a lot. As you mention, they're very good when the input is
> real-valued, and if you only need the magnitude output for a plot
> it'll be pretty efficient.
>
> Since processing power and memory are cheap these days everybody just
> plugs in FFTs. When computing or memory resources are hard to come
> by, though, the FHT can have some real advantages.
I thought that, when using the trick of an N-point FFT to get the
transform of 2 N-point real sequences, the FHT has no computational
advantage whatsoever over the FFT? But to answer Richard's question,
there's nothing wrong or disadvantageous in using it.
--
% Randy Yates % "The dreamer, the unwoken fool -
%% Fuquay-Varina, NC % in dreams, no pain will kiss the
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