To measure and display the amplitude of various frequencies of sound using a fast Fourier transform:

  1. Connect a microphone to any analog channel on the LabQuest or choose Sensor Setup from the Sensor menu and check Internal Microphone and choose OK.
  2. 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 location of the LabQuest’s internal microphone varies by device).
  3. Press the Collect button to collect the data.
  4. After data collection completes, tap Analyze > Advanced > FFT > Sound Pressure.
  5. 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.
  6. You can also get information about other frequencies by choosing their locations on the screen.
  7. 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:

  1. Choose Delta from the Analyze menu. Drag from peak to peak across several (e.g., 5) waveforms. Write down the Delta X (time) value.
  2. Choose the Calculator from the Home screen (for LabQuest 2 the calculator is accessed from the Accessories folder), enter the Delta X value you measured, and divide it by the number of waveforms to determine the period for one wave.
  3. Choose X^-1 on the calculator to determine the Frequency from the Period.

What is the best procedure to get a clean sine wave when using a tuning fork with the microphone?