How to Read Pitch on an Oscilloscope

If you're curious about the waveshape made by the sound of a musical instrument, you can observe it on an oscilloscope. You can also use the oscilloscope to find the pitch of the instrument. You can find the pitch by measuring the time period of a couple of wave cycles and doing a simple calculation.

Difficulty: Moderately Challenging

Instructions

Things You'll Need:

• Musical instrument
• Oscilloscope
• Microphone
• BNC cables and adapters

1. Connect the instrument to the oscilloscope, using the BNC cable and adapter. If you're using a traditional instrument, connect a microphone to the BNC cable.

2. Turn the oscilloscope and instrument on.

3. Set the oscilloscope's horizontal sweep rate to 1 millisecond/division or faster.

4. If you're using a microphone, set the vertical Volts/Division to 1 or 2 millivolts. Otherwise, set it to .5 volts.

5. Switch the coupling to AC.

6. Have a friend play and hold a note on the instrument.

7. 
    
   Measuring Two Full Cycles

   On the oscilloscope screen, count the horizontal divisions for two full wave cycles. Include any fraction of a screen division, since it might not be a whole number.

8. Calculate the frequency of the signal by dividing 2 by the number of horizontal divisions times the sweep speed (seconds per division). Example: 2 / (5.3 * .001) = 377.36 cycles per second. Refer to a conversion chart to convert frequency to musical notes (see Resources).

Tips & Warnings

• Many instruments use 1/4 inch phone plug adapters. Others use RCA or another type connector. Some oscilloscopes can find the frequency automatically. Check the user manual. If your oscilloscope can store the waveform on the screen, you won't need to sustain the note.
• This method works for simple monophonic tones only, no chords, no vibrato or other effects. While an oscilloscope can show you an instrument's frequency, use a calibrated standard for tuning. This method works best for instruments like an organ or synthesizer that can sustain a note. You'll need to sustain the note for several seconds while you do the measuring.

Resources

• Frequencies of Musical Notes