Binaural fusion experiments require earphone listening because this allows us to control precisely the stimuli presented to the two ears, as well as how these signals are related. The intriguing aspect of binaural beats is that they occur even though the two signals are acoustically completely isolated from one another. Binaural beats differ from monaural beats in several ways. Whereas monaural beats can be heard for interacting tones across the audible frequency range, binaural beats are associated with the lower frequencies, and the best responses are for tones between about 300 and 600 Hz. Binaural summation also occurs for loudness, as we all know from the common experience that a given sound is louder when heard with two ears than with one. Binaural interference occurs when a listener's experience of binaural phenomena for high frequencies is affected by the simultaneous presence of low frequencies.