Abstract: A system includes an electronic stethoscope producing a quasi-periodic signal, a processor, and a memory device with stored instructions that, when executed by the processor, cause the system to receive a representation of the quasi-periodic signal, to remove a DC component from the received representation of the quasi-periodic signal to produce a purely time-varying signal, and to filter, the time-varying signal to produce a pre-processed signal. A portion of the pre-processed signal is auto-correlated with itself, and a corresponding auto-correlation output is stored. A biphasic tapering function is applied to the auto-correlation output and produces a first maximum, the function including a time constant parameter that is a function of the quasi-periodic signal. A representation is stored, based on the first maximum, as an indication of a rate or frequency of the quasi-periodic signal.

Abstract: A method for localizing a pattern in a quasi-periodic signal includes estimating, using a controller, a rate or a frequency of a quasi-periodic signal, and defining a search window based on the estimated rate or frequency of the quasi-periodic signal. A starting position is defined in the received quasi-periodic signal, the starting position corresponding to a first maximum. A portion of the quasi-periodic signal in the search window is cross-correlated with a template signal pattern to be matched to produce a second maximum. The second maximum is defined by the controller as a new starting position. The new starting position is stored.