N step fft in D language

[John Colvin]

On Sunday, 15 September 2013 at 15:15:28 UTC, Kadir Erdem Demir 
wrote:
> I am using fft function from std.numeric
>
> Complex!double[] resultfft = fft(timeDomainAmplitudeVal);
>
> The parameter timeDomainAmplitudeVal is audio amplitude data. 
> Sample rate 44100 hz and there is 131072(2^16) samples
>
> I am seeing that resultfft has the same size as 
> timeDomainAmplitudeVal(131072) which does not fits my 
> project(also makes no sense).

That's what the FFT does. See here: 
http://stackoverflow.com/questions/4364823/how-to-get-frequency-from-fft-result