Abstract

Sound monitoring apparatus is described which provides a slowed down version of the original sound, e.g. a heart beat without changing the quality of the sound as perceived by a trained listener such as a physician. The amount by which the sound is slowed down can be varied by the user. The original sound is converted to an analog electrical signal, digitized and electronically processed in a microprocessor-based circuit such that digital data corresponding to cycles of the analog signal are stored in a random access memory. The microprocessor reads out the digital data a predetermined number of times corresponding to a number of sound cycles according to the rate set by the physician. The digital data is reconstituted into sound which is composed of replicated sets of cycles of the original sound. The repetition rate of the heart-beat in the output sound is a fraction of the repetition of the heart-beat in the original sound but the sound quality appears the same to the physician as the pitch is invariant. In a preferred embodiment stored digital data corresponding to each input half signal is duplicated and data corresponding to the duplicated positive half-cycle is inverted to give data corresponding to a negative half-cycle and the non-duplicated negative half-cycle data is inverted to give a positive half-cycle data. In another embodiment, the signal processing circuitry is incorporated into a conventional stethoscope and the circuitry is implemented using low power CMOS technology. The invention has application in other fields such as vibration analysis.

Other References

• Fairbanks et al., "Time or Frequency Compression-Expansion of Speech" Reprinted from Transcripts of National Convention of I.R.E.-Professional Group on Audio AU2-No. 1, 1954
• Francis F. Lee, "Time Compression and Expansion of Speech by Sampling Method" Journal of Audio Engineering Society, vol. 20, No. 9, Nov. 1972, pp. 738-742