Spontaneous otoacoustic emissions (SOAEs) are amplitude-modulated pure sinus tones. The character of the sinus tone, which is a rare phenomenon in nature, can be proven by resolving the shifts and drifts that more or less always occur. In this report amplitude modulation was studied by digital filtering. The SOAEs were composed of bursts which, in small emissions, appeared only a part of the time. This procedure is not only suited for studying SOAEs but also for demonstrating evoked emissions, even without averaging.