Abstract: Measurements of body sounds in the ear canal may be used for many applications. However, reliability is dependent on the ear canal being properly sealed to allow the body sounds to achieve a detectable level. An apparatus is therefore provided for determining a seal quality indication for a seal of an ear canal. An ear canal microphone (201) provides a microphone signal to an input (203) which is coupled to a circuit (205) for generating a first signal from the microphone signal. The first signal may be the same as the microphone signal. A circuit (209) then determines the seal quality in response to the frequency spectrum for the first signal. A frequency transformer (207) may perform a frequency transformation on the first signal to generate a frequency spectrum for the first signal and. The seal quality indication may specifically be generated based on a detection of a low frequency boost.