Algorithms Index , Filtering in Triana , Triana Spectral Storage Model


HighPass

Author : Bernard Schutz

Version : 2.0

Input Types : ComplexSpectrumSpectrumTimeFrequency
Output Types : ComplexSpectrumSpectrumTimeFrequency
Date : 04 Mar 2001 

Contents


Description of HighPass

The unit called HighPass performs a high-pass filter in the frequency domain. It takes an input spectrum and ouputs a narrow-band spectrum consisting of just the spectral elements above the lower-frequency cutoff chosen by the user in the parameter window. If the input is two-sided, the output contains both negative and positive frequencies whose absolute value exceeds the cutoff.

The user can also choose to smooth the edges of the frequency cutoff using a choice of window functions. The functions are those given in WindowFnc. These are useful if the filtered spectrum is to be inverted back to the time-domain: a sharp cutoff gives unwanted oscillations in the time-domain that are suppressed if the cutoff is smoothed.
 

Using HighPass

HighPass's parameter window (double-click on the unit) looks like this.

The first slider chooses the frequency cutoff in Hz. All data at frequencies below this are set to zero.

The second line is a choice box. Select this if you want narrow-band output. If it is not selected (the default) then the output spectral data set will have the same length as the input but the filtered data elements will be set to zero. If you choose narrow-band, then these zeros will not be present in the output: this saves storage. The FFT unit will invert this properly.

The third choice is the window function that can be used to smooth the edges of the frequency cutoff.