Primary Beats and Combination Tones

When two sine waves of equal amplitudes but different frequencies are played simultaneously, several interesting sounds can be heard. 


Two tones are presented with equal amplitude.  One remains at the starting frequency.  The other starts at the same frequency and its frequency gradually increases.  Three frequency excursions of differing lengths are possible.

Starting frequency [Hz] (default is A above middle C)

MUTE       

Beats with constant frequency shift:     Df = 1 Hz     Df = 5 Hz     Df = 10 Hz

Two tones are presented with equal amplitude.  One remains at the starting frequency.  The OTHER starts at the same frequency and its frequency gradually increases.  Three frequency excursions of differing lengths are possible.

Short Ramp (Primary beats)     Medium Ramp (Roughness)     Wide Ramp (Combination tones)

Above figure for two pure tones is from Rossing, Moore and Wheeler, 3rd edition. This demonstration was created by Dan Boye using the Java2 sound interface written by Todor Penev.