You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A SURVEY OF AUDIO PROCESSING ALGORITHMS FOR DIGITAL STETHOSCOPES 
Chapter Title:  DIGITAL STETHOSCOPE 
1. Abstract of Cited Paper (BIB001):  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. 
2. Abstract of Cited Paper (BIB002):  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

Literature Review:
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.