To measure and display the amplitude of various frequencies of sound using a fast Fourier transform:
- Connect a microphone to any analog channel on the LabQuest or LabQuest 2 unit or choose Sensor Setup from the Sensor menu and check Internal Microphone and choose OK.
- Prepare your sound source, such as a tuning fork, musical instrument, or telephone keypad. Hold the source a few centimeters from the end of the microphone (the LabQuest internal microphone is located at the top right corner of the unit face).
- Press the Collect button.
- From the Graph tab, choose Analyze > Advanced > FFT > Sound Pressure.
- The Fast Fourier Transform display will show amplitudes for various frequency intervals across a spectrum. In the bottom right corner, the peak frequency is displayed.
- You can also get information about other frequencies by choosing their locations on the screen.
- After you choose OK, the peak frequency determined by the Fast Fourier Transform is displayed alongside the original graph.
With pure tones, you can also calculate the period and frequency by measuring the time between peaks:
- Choose Delta from the Analyze menu. Drag from peak to peak across several (e.g., 5) waveforms. Write down the Delta X (time) value.
- Choose the Calculator icon on the Panel, enter the Delta X value you measured, and divide it by the number of waveforms to determine the period for one wave.
- Choose X^-1 on the calculator to determine the Frequency from the Period.