Re: Complex to 2x real - how?

cs_posting@[EMAIL PROTECTED]
 writes:

> On Oct 10, 1:31 pm, Randy Yates <ya...@[EMAIL PROTECTED]
> wrote:
>
>> ? If the ****tion of the spectrum that was from 0 to Fs / 2 is reversed,
>> or placed in a contrary order, with that from Fs / 2 to Fs, then how
>> is that not inverting?
>
> It would be (partially) inverting if that is what were to happen.

No, it would be inverting (in the colloquial sense) if that is what
occurs. Since that is what occurs, and I was speaking colloquially, it
is indeed inverting.

> But that is NOT what happens in the described method.

That is exactly what's happening.

> In the described method, a constant offset is added to the frequency,
> so what  was  negative is now slightly positive, and what was positive
> is now even more positive.  

You can look at it that way. Or you can look at it in the way I have
proposed.

This can be seen by simply acknowledging that, in the original signal,
the spectrum from -Fs / 2 to 0 is precisely the same as that from Fs / 2
to Fs. Whether you think of it as the lower half of -Fs / 2 to +Fs / 2,
or the upper half of 0 to Fs, it's the same information.  In one case
it's the lower half of the "z*****h" image, and in the other case it's
the lower half of the first image.

> There's no flipping, only a constant ****ft upwards in frequency.

Oh, but there is if by "flip" you mean the spectrum pieces from 0 to 
Fs / 2 and from Fs / 2 to Fs. And that's precisely what I meant.
-- 
%  Randy Yates                  % "I met someone who looks alot like you,
%% Fuquay-Varina, NC            %             she does the things you do, 
%%% 919-577-9882                %                     but she is an IBM."
%%%% <yates@[EMAIL PROTECTED]
>           %        'Yours Truly, 2095', *Time*, ELO 
 
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