Differnce between the phase obtained by FFT and the hilbert transform

hey guys,
We can get the phase of a signal by performing the FFT (from the real and
imaginary components) on the signal. If we perform hilbert transform on a
signal it  gives us analytical signal from which we can get the
instantaneous phase of that signal. How the phase of a signal obtained by
performing FFT differs from the phase obtained by using hilbert transform.
Is there any differnce ? if yes, what is it? 

Thanks in advance,
Rajan.

Rajan wrote:
> hey guys,
> We can get the phase of a signal by performing the FFT (from the real and
> imaginary components) on the signal. If we perform hilbert transform on a
> signal it  gives us analytical signal from which we can get the
> instantaneous phase of that signal. How the phase of a signal obtained by
> performing FFT differs from the phase obtained by using hilbert transform.
> Is there any differnce ? if yes, what is it?
>
> Thanks in advance,
> Rajan.

The HT gives phase vs time. The FFT gives phase vs frequency.

John

>
>Rajan wrote:
>> hey guys,
>> We can get the phase of a signal by performing the FFT (from the real
and
>> imaginary components) on the signal. If we perform hilbert transform on
a
>> signal it  gives us analytical signal from which we can get the
>> instantaneous phase of that signal. How the phase of a signal obtained
by
>> performing FFT differs from the phase obtained by using hilbert
transform.
>> Is there any differnce ? if yes, what is it?
>>
>> Thanks in advance,
>> Rajan.
>
>The HT gives phase vs time. The FFT gives phase vs frequency.
>
>John
>
>



John, Thanks for the reply,
The "hilbert" function is available in MATLAB - i.e. "hilbert(xr,n)" which
uses an n point FFT to compute the Hilbert transform. Does it give phase vs
frequency ? or phase vs time?

Rajan wrote:
> >
> >Rajan wrote:
> >> hey guys,
> >> We can get the phase of a signal by performing the FFT (from the real
> and
> >> imaginary components) on the signal. If we perform hilbert transform on
> a
> >> signal it  gives us analytical signal from which we can get the
> >> instantaneous phase of that signal. How the phase of a signal obtained
> by
> >> performing FFT differs from the phase obtained by using hilbert
> transform.
> >> Is there any differnce ? if yes, what is it?
> >>
> >> Thanks in advance,
> >> Rajan.
> >
> >The HT gives phase vs time. The FFT gives phase vs frequency.
> >
> >John
> >
> >
>
>
>
> John, Thanks for the reply,
> The "hilbert" function is available in MATLAB - i.e. "hilbert(xr,n)" which
> uses an n point FFT to compute the Hilbert transform. Does it give phase vs
> frequency ? or phase vs time?

It follows the FFT with an IFFT to go back to time domain.

John