Timbre: Harmonic Content of a Complex Tone
1 · Predict
A musical tone at 220 Hz sounds different from a pure sine wave at 220 Hz — it has 'color' or timbre. What's actually different about its sound wave?
- The tone is a mix of the fundamental plus higher harmonics at different strengths.
- The tone is just a louder version of the same pure 220 Hz wave.
- The tone has a different fundamental pitch than 220 Hz.
2 · Set Up
- Open the rich-timbre preset and press Reset. The source emits a 220 Hz fundamental blended with specific higher harmonics.
- Enable the harmonic spectrum display at the observer.
- For each row, read off the amplitude of the listed harmonic relative to the fundamental's amplitude.
3 · Collect Data
| Harmonic number n | Frequency n·220 Hz (Hz) | Amplitude ratio (vs. fundamental) |
|---|---|---|
| 1 | ||
| 3 | ||
| 5 |
Sketch the spectrum: a bar chart of amplitude ratio (y-axis) against harmonic number n (x-axis) for n = 1 through 5, including the harmonics not in your table (their ratio is 0).
4 · Analyze
- List the frequency of each harmonic in your table as n × 220 Hz, and compare your recorded amplitude ratios to the spectrum display.
- The 2nd and 4th harmonics have zero amplitude in this tone, while the 1st, 3rd, and 5th (all odd) are present. What does a spectrum with only odd harmonics tell you about the shape of the wave?
5 · Extend
- A clarinet's tone is dominated by odd harmonics, similar to this one, while a violin's tone includes strong even harmonics too. Explain why two instruments playing the identical fundamental pitch (220 Hz) still sound completely different.
- A tuning fork produces a nearly pure tone (only the fundamental, no higher harmonics). How would its spectrum bar chart look different from this experiment's?