Re: How do YOU handle this disparity in fft?

[Macy]

By the way, be very careful naming variables mnemonically. I just labeled the 
'sig with noise' as 'sign'. Well, you can see the problem when I went to do 
something else.

The program below allows you to preserve the energy in an 'actual' voltage 
waveform. Both, a 1 Vrms signal is returned as 1 and a DC signal of 1 Vdc is 
returned as 1.

You can easily add noise density function by putting in the value, 
vn=Vrms/rtHz, as
 noisesignal = vn*randn(1,vectorlength)*sqrt(samplingratepersec/2);
  where vn is the noise density function in v/rtHz, and
  vectorlength matches the signal length you add it to, and
  samplingratepersec is the sampling rate

fftreal.m

function [out,ford]=fftreal(in);
%  calculates the 'adjusted' values of the fft, only half the fft is returned
%  use the form [b,ford]=fftreal(sig);
%   the ordinate, ford, is returned to enable plotting, remember to adjust it. 
%       input a realtime waveform a vector only
%       out is the adjusted values of the fft in true energy values
%       ford is the ordinate of the fft, to accurately plot ford is to be 
multiplied by 
%        the Sampling rate divided by the packet length.

if (nargin ~=1)
  help fftreal;
  return;
endif

[rowsin,columnsin]=size(in);
if( rowsin ~=1)
  disp("for now, only accept a vector");
  return;
endif

if ( 2*round(columnsin/2+.1) ~= columnsin)
  disp("for now, only accept an EVEN vector");
  return;
endif

n=round(columnsin/2);
b=sqrt(2)*fft(in)/columnsin;
out=[b(1)/sqrt(2),b(2:n)];
ford=([1:n]-1)/n;

endfunction;


and, please, NO snickering at how simple this program is, it took a LONG time 
to get here.