Re: 4 Hz modulation energy

[Erick Gallun <gallun@xxxxxx>]

Arthur,

I would recommend first extracting the envelope by using either a halfwave
rectification (i.e., replace all the negative values in the time waveform
with zeros) or a Hilbert Transform and then lowpass filtering the waveform
at around 50 Hz (the lowpass is optional if you only care about the 4 Hz
component).   Once you have the envelope, simply do an fft (making sure
that your frequency resolution is at least 1 Hz) and look for the energy
around 4 Hz.  If any of these steps don't seem obvious too you, let me know
and I can send you some Matlab code.

Erick Gallun
Postdoctoral Fellow
Hearing Research Center, Boston University
http://people.bu.edu/gallun



At 03:30 PM 3/24/2005 +1100, Arthur Choi wrote:
> Dear all,
>
>     Could anybody tell me the method and the calculations on obtaining "4
> Hz modulation energy" for a speech signal?
>
> regards
> Arthur