SpectraPLUS-DT allows you to select any Sampling Rate supported by the currently selected DT-9800 data acquisition module. The measured frequency range is always 0 to 1/2 the Sampling Rate.
The Sampling Rate determines how many times a second that the analog input signal is "sampled" or digitized by the input device. A sampling rate of 10,000 Hz will sample the signal every .0001 second. The possible range of sampling rates are limited by the capability of your input device.
An important principal from digital signal processing is the "Nyquist Sampling Theorem" which states that any signal can be represented if sampled at least twice the rate of the highest frequency of interest. This means that if you wish to measure a 3,000 Hz signal, the sampling rate must be greater than 6,000 Hz. A note of caution: if there are unwanted signals which are greater than 3,000Hz, Aliasing will occur.
When a .WAV file is opened, the Sampling Rate and Format is changed to match the rate at which the file was originally recorded; the sampling rate cannot be changed - it must remain constant within a single .WAV file. The current sampling rate is always displayed in the status bar along the bottom of the application; the value corresponds to the channel who's plot has the "focus" (its title bar is highlighted).
See also: Aliasing, FFT size