SpectraPLUS-SC allows you to select any Sampling Rate supported by your sound card. The measured frequency range is always 0 to 1/2 the Sampling Rate divided by the decimation ratio.
The Sampling Rate determines how many times a second that the analog input signal is "sampled" or digitized by the sound card. 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 sound card.
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 recorded and the sampling rate edit box is disabled - the Sampling Rate must remain constant within a single .WAV file. When the .WAV file is closed, these settings will revert to their previous values. The current sampling rate is always displayed in the status bar along the bottom of the application.
To determine if your card supports a rate other than the displayed choices, simply enter the value in the edit control and press OK. The analyzer will attempt to use the specified rate and a message box will appear if it is unsuccessful.
See also: Aliasing, FFT size , Decimation ratio