Abstract :
This paper gives a brief survey of early and current work in the application of audio-frequency amplifiers, equipped with filters, to the diagnosis of abnormal heart conditions, and for use as teaching aids in medical schools. The possible application of a gating technique, i.e., filtering in time instead of in frequency, is discussed, and a description is given of some circuits which have been used for this purpose. Both filter systems have proved to be useful adjuncts to the stethoscope and, if used with a tape recorder, are valuable teaching aids.
