Sampling frequency and sweep frequency range

No. 5 is for setting the sampling frequency and frequency range if single sweep or multiple sweeps is selected as excitation.



If you want to measure at low frequencies only, first set the sampling frequency as low as possible.



Which sampling rates you can use depend on your sound card, some sound cards can go down to 8 kHz and even 4 kHz. WinMLS gives an error message when you start a measurement if the selected sampling frequency is not supported.


If you have selected sine sweep as stimulus, you can select the sweep frequency range as shown below.



Our experience is that the best results are obtained if the upper sweep frequency is set to Max as shown in the figure above. At least you should follow this: WE RECOMMEND THAT YOU SET THE LOWER FREQUENCY SOMEWHAT LOWER THAN THE LOWEST FREQUENCY YOU WISH TO MEASURE. For example, you with to measure down to 20 Hz. Then you should start the sweep at 16 Hz as shown in the figure above.


To increase the accuracy for low frequencies, the highest frequency can be set lower than  in the figure above which means half the sampling frequency. This is shown below



If the upper frequency is much lower than the Nyquist frequency (Fs/2), resampling is used to reduce the file size. This means that after the measurement is performed, the measurement is processed so that the high frequencies above the selected upper frequency are removed.

Note: The result of the resampling process depends on the measurement settings. You should first perform a loopback measurement of the sound card to check the result. If it has ripple in the frequency response that is too high for your application, increase the measurement duration and try again. Best results have been reported if you select the settings in step no. 6 as shown below


(Note:  will not be displayed if single sweep mode is selected in no. 3)


In sweep settings (advanced mode), the resampling can be turned off if that is desired.