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Decimation

The decimation ratio value controls the ratio with which the digitized audio is down-sampled". This feature is used to achieve a lower sampling rate <sampling_rate.htm>. This will allow greater frequency resolutions at low frequencies for vibration measurements and similar applications. For instance, if the sampling rate is 8000 Hz, decimating by a factor of 10 will effectively reduce this to 800 Hz. The resulting measurement range will then be 0 to 400 Hz.
A value of 1 will not decimate the data at all.

Decimation is actually a very simple process. Let's say we want to down-sample by a factor of 8:1, all we need to do is to throw away 7 out of every 8 samples. 
You need to be careful when decimating to make sure that the original signal contains no energy above the "new" Nyquist frequency otherwise aliasing will occur. If this is not the case you should either use an external low pass filter or check the box labeled "Apply Low Pass Filter when Decimating".
Note:
The Time Series view always displays data prior to the decimation process.
See also:  FFT Size, Filtering