Summation Tones
Text: Helmholtz worked out the theory, mathematically, and proved that two tones with given vibration numbers, may not only produce a third tone, having its vibration number equal to their difference (Difference Tone), but also another tone equal to their sum. Tones will also sum with the Difference Tones present and their harmonics (overtones) and all other partials producing a plethora of vibration numbers.
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