Filtering an FFT signal without losing frequentie information

[Guus]

Hello everyone,

I'm building a VI based on Formant_Excercise to explain speech coding. The problem I'm having is that I can't filter a FFT signal with a lowpass filter so I have to use moving averege. But than the places of the peaks change. Does any one of you know how I can get the peaks of the FFT because I want the formants of speach and the Formant_Excercise vi cant get high frequentie peak because he does not filter the FFT. I added the program but I wan't able to to include the ee vowel but that can be found at this link http://forums.ni.com/ni/board/message?board.id=170&message.id=69182&query.id=68761#M69182 

Best regards,

Guus

[BasvanDijke]

Hi Guus,

You can use the Filter vi, but then you have to choose the right cutoff frequency.

The input signal of this vi contains the FFT data of the signal (no time data). The frequency steps of this signal are 4,8Hz. The filter vi interprets this FFT result as a time sampled signal with 0.20S/s.

 This means a samplefrequency of 0.20S/s. In order of the nyquist theorem, the maximum frequency component that can be recognized is 0.5*0.20= 0.10 Hz.

The maximum cutoff frequency can be 0.10Hz (wich is equal to your highest frequency component in your original time signal).

Regards,

Bas

[Guus]

Thnx for your response,

I will try to implement this in my program and I will let you here what the results are.

Guus