BobW wrote:
> "Jerry Avins" <jya@ieee.org> wrote in message
> news:b3s2m.2448$066.1548@newsfe08.iad...
>> BobW wrote:
>>> "Jerry Avins" <jya@ieee.org> wrote in message
>>> news:bfq2m.2441$066.810@newsfe08.iad...
>>>> BobW wrote:
>>>>
>>>> ...
>>>>
>>>>> I found the answer. It was in the last place I looked.
>>>> Almost inevitably. Having found it, why look further?
>>>>
>>>> ...
>>>>
>>>> Jerry
>>> Yes. I was merely trying to add a little bit of humor to this
>>> otherwise-dry newsgroup.
>> It alternates. Sometimes the humor gets laid on thick. (When I attempt it,
>> it often falls flat.)
>>
>>> I sense that this technique of packing real data samples into the
>>> imaginary part of the input to the FFT is rather uncommon. Is that your
>>> take, too?
>> No. The technique seems to be widely known, but rarely needed. There are
>> real-to real FFT libraries available that do the scut work for the user,
>> as good libraries should.
>>
>> Jerry
>
> I certainly have found many real-to-real FFT routines, but the one that's
> available for my microcontroller merely stuffs zeros into the imaginary data
> input locations and then returns the magnitude of the outputs.

So you wrote a better one. The pressure to meet a deadline sometimes
leads to inferior work.

> This particular technique, described by Mr. Lyons, puts the real data input
> samples into the imaginary inputs (rather than just setting them all to
> zero). The advantage is that the input data buffer size can be cut in half
> (for a particular input data set).
>
> Is it your experience that the "Lyons" technique is commonly used?

Just an assumption. I think that I remember FFTW's library function
doing that. I've used an assembly-language version for the TMS320C34
that one of their application programmers sent me.

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