Lambda SR1, Руководство по эксплуатации, Страница: 151 / 317

SR1 Operation 151
© 2014 Stanford Research Systems
Spectrum w ith Blackm a Window
To eliminate the discontinuities between the beginning and end of the time record the time record is
typically multiplied by a window function which is large in the middle of the time record and tapers off
near the beginning and end of the time record. The second spectrum shows the same two sine waves
after application of a window function.
Many window functions have been developed over the years, but few have the >120 dB dynamic range
necessary for modern audio measurements. For most measurements with SR1, the Rife Vincent 4-term
or the Blackman- window are the best windows to use. (The Blackma window is a
proprietary improved version of the traditional Blackman Harris window.) These two windows have
sufficient dynamic range for most measurements. The other windows are included for historical interest
and comparison purposes. The Uniform window should be used when use the FFT chirp, log-sine chirp,
or Multitone source is used.
Phase Controls
The linear spectrum has phase as well as magnitude associated with it. Checking "Unwrap Phase"
instructs SR1 to "unwrap" the phase by adding or subtracting 360º at appropriate break points to create
a continuous phase curve.
Phase Spectrum of 1 kHz LPF Without Unw rapping