Beats with two tone generators
The tone generators were tuned to essentially the same pitch and then one was slowly tuned up or down. The result was a strong pulsating tone, the pulsations becoming more rapid as you tune farther away either upward or downward in pitch. The two displays above show the combined tones on a fast sweep to show the wave shape, and on a much slower sweep to show the rising and falling amplitude of the combined sounds.
The above sound amplitude trace shows the beat phenomenon as one tone generator is tuned upward in pitch.
Traveling wave concepts