A SURVEY OF AUDIO PROCESSING ALGORITHMS FOR DIGITAL STETHOSCOPES <s> DIGITAL STETHOSCOPE <s> BACKGROUND ::: To provide an objective method to support and teach auscultation, a new portable system (graphic display system) was evaluated for graphic display and printing of heart sounds. ::: ::: ::: METHODS ::: Ninety-one patients from three institutions, with a variety of heart sound abnormalities, were studied by two examiners. A graphic recording was made in each and compared with the auscultatory findings. ::: ::: ::: RESULTS ::: The findings of the graphic system confirmed the auscultatory impressions of both examiners in 77 (85%) of the 91 cases. Brief sound transients, such as split second sounds and ejection sounds, third heart sounds, and prosthetic opening and closing sounds, were all regularly recorded with the graphic system, often allowing resolution when examiners were in disagreement. Graphic recordings commonly were at variance with examiners in detecting fourth sounds, possibly because of examiners' difficulty in distinguishing these from split first sounds as well as limitations of the graphic system itself. High-pitched murmurs of low intensity (< grade 2), as exemplified by those of aortic and mitral regurgitation, were occasionally missed by the graphic system, probably because of baseline interference by background noise. ::: ::: ::: CONCLUSIONS ::: The graphic display system can often provide more information than can be obtained by standard auscultation alone, especially in the detection of low-frequency and multiple sounds, and in the accurate timing of intervals. It is often unable to detect soft high-frequency murmurs. Permanent records allow for more objective comparison of the auscultatory findings of various examiners at different times. This system provides an excellent means by which auscultation skills may be taught or enhanced, especially since its speed and portability allow immediate feedback for comparison with auditory perceptions. <s> BIB001 </s> A SURVEY OF AUDIO PROCESSING ALGORITHMS FOR DIGITAL STETHOSCOPES <s> DIGITAL STETHOSCOPE <s> The objective of the present paper is to provide a detailed review of the most recent developments in instrumentation and signal processing of digital phonocardiography and heart auscultation. After a short introduction, the paper presents a brief history of heart auscultation and phonocardiography, which is followed by a summary of the basic theories and controversies regarding the genesis of the heart sounds. The application of spectral analysis and the potential of new time-frequency representations and cardiac acoustic mapping to resolve the controversies and better understand the genesis and transmission of heart sounds and murmurs within the heart-thorax acoustic system are reviewed. The most recent developments in the application of linear predictive coding, spectral analysis, time-frequency representation techniques, and pattern recognition for the detection and follow-up of native and prosthetic valve degeneration and dysfunction are also presented in detail. New areas of research and clinical applications and areas of potential future developments are then highlighted. The final section is a discussion about a multidegree of freedom theory on the origin of the heart sounds and murmurs, which is completed by the authors' conclusion. <s> BIB002 </s> A SURVEY OF AUDIO PROCESSING ALGORITHMS FOR DIGITAL STETHOSCOPES <s> DIGITAL STETHOSCOPE <s> Last year at the EMBC 2004 in San Francisco, we presented a paper entitled: "Digital Phonocardiography: a PDA-based Approach", which introduced the development of a PDA-based biomedical instrument capable of acquiring, processing, and analysis of heart sounds. In this paper we present a system, which is not only able to record and display the heart sounds in a pocket PC but also apply several signal processing and statistical techniques to segment the these signals into four parts (the first heart sound, the systole, the second heart sound and the diastole) and implement feature extraction methods for classification purposes. Classification has been achieved using a multilayer perceptron (MLP) artificial neural network (ANN). The system was used to classify a number of normal and abnormal heart sounds (normal, aortic regurgitation, aortic stenosis, mitral regurgitation and mitral stenosis) and validate the effectiveness of the statistical segmentation and the feature extraction methods in this environment <s> BIB003
It is essential that we define digital stethoscope since there can be various interpretations from the name alone. Traditional stethoscopes depend solely on acoustics to amplify and transmit the heart sounds to the clinician. The concept of electronic stethoscope arrives when electronic components were first used to amplify, filter and transmit the sound (Fig.1) BIB002 . There are various examples in literature regard- ing the development of digital and electronic stethoscopes. Bredesen and Schmerler (Bredesen and Schmerler, 1991) have patented an "intelligent stethoscope" designed for performing auscultation and for automatically diagnosing abnormalities by comparing digitized sounds to reference templates using a signature analysis technique. Several other electronically enhanced and digital stethoscopes have been developed and described in literature (F. L.  BIB001 BIB002 BIB003 . Fig. 2 shows a block diagram of a digital stethoscope prototype developed by our group. The auscultation quality was considered satisfactory in clinical trials when compared to auscultation using acoustic stethoscopes, but clinicians still perceived differences in audio pitch although this did not affect their ability to diagnose heart conditions. Our field experience confirms Durand's BIB002 opinion that audio enhancement alone is not enough for the clinical community to adopt this new technology. In order to make digital stethoscopes attractive to clinical cardiologists, we clearly need to address the numerous potential improvements provided by a fully functional, robust digital stethoscope: real-time acquisition, analysis, display and reproduction of heart sounds and murmurs. Digital stethoscopes must also open the doors for digital audio archives, simplifying the acquisition, storage and transmission process of cardiac exams and murmurs, potentiating functionalities such as the teaching of auscultation, telemedicine, and personalized healthcare.