Re: [Discuss-gnuradio] FFT --> IFFT

[Robert James]

On 11/18/13, Tom Rondeau <address@hidden> wrote:
> On Mon, Nov 18, 2013 at 8:22 AM, Robert James <address@hidden>
> wrote:
>> On 11/18/13, Marcus Müller <address@hidden> wrote:
>>> Hi Robert!
>>>
>>> This is strange -- but could be explained by the fact that numerical
>>> inaccuracy don't allow us to *exactly* recreate all values during
>>> fft-ifft
>>> operation.
>>> Also, make sure you use a rectangular window.
>>
>> Wow, switching to a rectangular window of fft_size solved it! I'm
>> baffled: I know windows are a way of pretransforming the wave prior to
>> FFT, to eliminate artifacts.  I just used the default window.  Why did
>> I need a rectangular window here? In what other cases do I need it?
>
> Were both windows the same or different? I've often seen people trying
> this experiment using a window on the forward FFT but no window on the
> inverse FFT. That would obviously cause different output results.

Both were the same - the default blackmanharris, set to the ftt_len size