FAQ
 
 The Impulse Control Window

 The Frequency response function subtracts the response of a signal from that of a reference on a frame by frame basis. A second
 algorithm then finds the effective time displacement, allowing the software to directly unwrap phase (we do not use minimum
 phase calculations). The frequency domain information is then reversed back to the time domain revealing the impulse response,
 including reflections, but in this case with an accurate time position within the new time window. A 'start' and 'stop' reference
 can then be easily added to the impulse allowing the user to reject room reflections.

 Note:

 Time 'start' and 'stop' ticks also effect the reponse in the main control window. However, these time ticks can only be defined
 when the Impulse Window is active. If the Impulse window is not active, the entire frame is assumed.


 Waterfall 'Forward Time' FFT

 The 'Forward Time' waterfall FFT plot shows FFT response slices as a function of time as the time window grows from the right
 hand side. This view shows how the FFT bin energy grows as time progresses until a steady state condition is achieved. Tick marks
 '1' and '2' can be moved to change the starting and stopping time positions. The following example is for a Heil AMT tweeter,
 intentionally placed ~1M from the corner of the room to produce a strong reflection.

 
                       Click Image to Enlarge


 Cumulative Spectral Decay (CSD)

 Reversing the window growth and showing FFT slices as a function of time as the time window shrinks from the left hand side
 results in the CSD display.In this case the FFT bin energy shows how the spectrum changes as energy is removed.As before Tick
 marks '1' and '2' adjust the starting and stopping time positions.The following example is for a Heil AMT tweeter, intentionally
 placed ~1M from the corner of the room to produce a strong reflection.

 
                       Click Image to Enlarge


 Frequency Domain Smoothing and Sharpening

 The number of FFT bins that are combined to make an entry in the display data is adjusted here. That is, a per octave resolution
 is defined here.


 Controlling the Transition Region

 The lead in and lead out transition region can be 'smoothed' using a modified raised cosine window function. However, since
 the impulse response has been located in time using a frequency domain technique, windowing the impulse in a traditional
 sense is not required.  Never the less, this adjustment may help in some cases.


 Sizing and Rotating the Display

 Use the arrow, page up, page down, insert, delete, home and end keys to size and rotate the display. Additional controls are
 provided to view data in 'slices', 'sheets' and wire frames.



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