Cut 'n Window

Description
Basically CutNWindow is a function to cut a desired part of a pulse response. If e.g. a filter is convolved​​​ with another filter the filter length doubles. Since the convolved filter needs to be the correct length for further use, Cut 'n Window allows it to be “trimmed” down to size.

Options:

• Length: Specifies the output filter length. The combobox allows a quick selection of preferred lengths (power of two). The edit field allows to define also other lengths.
• Position/Count: Together with the radio buttons to the right and the checkbox below, specifies where the new filter starts and ends
• Start position: If selected, Position/Count specifies the beginning sample of the new filter relative to the beginning of the input filter
• before Peak: If selected, Position/Count specifies the beginning sample of the new filter in samples before the maximum peak of the input filter. Higher Position/Count therefore moves the first sample of the new filter to the left, or earlier in time, which is the opposite behavior to the case where Start position is selected.
• Before peak in area !: It is possible to select an area by setting the markers in the time-domain chart (left/right mouse-click). Then CutNWindow uses the max. peak within this area as reference. This allows e.g. to cut a part around a peak caused by reflections. It the markers are not defined then the comment “! not allowed !” appears.
• peak symmetric: The new filter starts exactly half its length before the peak. If checked, Position/Count is ignored.
• Remove DC: a filter pulse response can contain a DC offset. It will be removed if the checkbox is ticked. Usually a good idea to leave checked. (Leave it checked unless you have a specfic reason and know what you are doing.)
• Window (Blackman Optimal): Occasionally needed when Cut 'n Window is used to shorten filters if the beginning or end of the output filter occurs at a time when the value of the input filter is significantly different from zero. In this case it removes spurious high frequency components that would otherwise be created, at the cost of some modification of the frequency response. However a filter so short inevitably leads to compromises.