CA2265690C - Digital telephonic system for stethoscope signal processing - Google Patents

Abstract

The present invention relates to digital telephonic system for stethoscope signal processing. Stethoscope sounds are converted to electrical signals and conveyed in digital format to an RS 232 data port (27) of a data transmission product. In the alternate, a modem (26) can be used to convey the signal via a home telephone line. At the receiving end, the reverse process takes place to convert the data back to audible sound. The fidelity and accuracy of the stethoscope sounds is maintained at the receiving end using asynchronous data communications and error protection techniques.

Description

CA 02265690 l999-03- 11WO 98/11711 PCT/US97l1l394DIGITAL TELEPHONIC SYSTEM FORSTETHOSCOPE SIGNAL PROCESSINGFIELD OF THE INVENTION5 The present invention relates generally to stethoscope devices.1015202530More particularly, the present invention relates to a digital method anddevice for the transmission of stethoscope sounds from a patient at alocation and the reception of high quality auscultation sounds, in real-time, by a doctor at another location utilizing a low bit rate and a regulartelephone line or an equivalent interface.BACKGROUND OF THE INVENTIONA stethoscope examination is one of the most essential parts of aroutine physical examination. Generally, stethoscope examinations areconducted by a doctor using a bell-and-diaphragm chest piece to listen tothe sounds generated by the patient’s cardiovascular and respiratorysystems. The bell isolates sounds in a lower frequency range, while thediaphragm passes higher frequency stethoscope sounds.One of the basic requirements of a stethoscope examinationprocedure is the need to maintain a doctor-patient interaction. Generally,the patient is required to be physically present to enable the doctor toperform the examination. Consequently, patients who need frequentstethoscope examination are faced with the burdensome prospect offrequently visiting their doctor at a hospital or clinic. These difficulties areparticularly burdensome to patients who live in remote areas and whoneed to see a doctor on a regular basis.Accordingly, there is a need for a system by which a doctor canperform medical examinations on a remotely-located patient. Preferably,such a system would enable the doctor to perform a medical examinationon a patient remotely having the advantage of a real-time evaluation andinteraction with the patient.While many techniques for sensing and transmitting data fromremote locations are known, the use of a telephone line as a medium ofhigh quality auscultation sounds poses unique challenges. Fidelity of thesignal presented to the doctor's ears is of critical importance, because theW0 98/117111015202530CA 02265690 l999-03- llPCT/US97/11394- 2 -doctor's opinion depends on distinguishing subtle sound patterns. Thesounds of greatest interest are relatively low frequencies, generally in therange of 30 to 500 Hz. The possibility for a medical doctor far away from apatient to hear reliable and accurate stethoscope sounds will enhancehealth delivery. However, the home telephone line transmits the desiredrange of frequencies rather poorly.Telephone signals are inherently analog. This means that theelectric signal varies with the level of the sound. However, it is now Wellknown in the art that the quality of the transmission of sound signalsbetween switches could be improved and accomplished at a lower price bydigitizing the signals. Digitizing is a form of coding. Coding is generallydefined as a process of transforming messages or signals in accordancewith a definite set of rules. Any analog signal can be converted to a digitalsignal through sampling and quantizing.Accordingly, a digital telephonic stethoscope system must employexisting public service telephone signals and digitize them to transmitinformation in the low frequency range. Further, doctor-patientinteraction must be maintained on a real-time basis to enable a remotereal-time evaluation and diagnosis of the patient.SUMMARY OF THE INVENTIONThe present invention provides a digital telephonic system whichadvantageously employs digital techniques for the transmission of theauscultation data. The techniques disclosed in the present inventionenable the transmission of high quality sound over a relatively smallbandwidth. Specifically, the present invention enables the use of lowpriced modems over normal telephone lines at a reduced bandwidth.Existing art requires large bandwidth, generally in the range of 32-128 Kb / s, and are relatively expensive for digital telephonic stethoscopesound transmission. Large or wide band digital systems cannot be usedover normal telephone lines or in other low cost and low bandwidthapplications.W0 98/117111015202530CA 02265690 l999-03- llPCT/U S97/ 11394_ 3 -Generally, the present invention provides a digital—basedstethoscope which sends stethoscope sounds from a patient over a datacommunications channel to a doctor or nurse to thereby allow a real—timetransmission of auscultation sounds for diagnosis and evaluation.Primarily, two stations, a doctor's and a patient’s station, are remotelyconnected via intermediate digital equipment such that analog signalsfrom a chest piece at the patient’s station are converted to digital signalsand are sent through a modem or multiplier to another modem ormultiplier at the doctor's station. The present invention utilizes a circuitto sample the analogs and quantize them into digital format. Quantizinginvolves comparing each of a sample amplitude against a list of discretesample intervals. Each discrete interval is described by a code, a binarynumber. The process used is called pulse code modulation (PCM).Thereafter, a PCM decoder translates the binary data into analog signalswhich are presented to the doctor through a headset.One of the many unique features of the present invention is theenablement of high-fidelity sound transmission over low bit rate datachannels. Primarily, only a small number of quantization levels are usedfor the PCM and require only a small number of data bits. To compensatefor the small number of bits, a companding procedure is implemented tominimize the amount of quantization noise by taking advantage of thenature of the stethoscope signal. Companding involves compression andexpansion.provides 12-bit PCM resolution with only 8 bits.Using the companding process, the present inventionFurther, one of the many unique optional features of the presentinvention includes error handling to prevent retransmission of corrupteddata. Error is checked by transmitting a parity bit with the data. When anerror is detected at the receiving end, the corrupted byte is discarded and itis replaced by the byte occurring just prior to it. This results in the PCMdecoder receiving the same data twice.Yet another unique feature of the present invention is the use ofasynchronous transmission to provide a simple low cost framing scheme.CA 02265690 2004-06-22Asynchronous transmission is not typically used in real-time applications.Asynchronous transmission is implemented in such a way as to maintain real-timedata flow very simply at a low cost.Another feature of the present invention includes an optional use of anadaptive differential PCM (ADPCM) encoder. The ADPCM encoder translates thevalue of each byte into a differential value which represents the decrease or increasefrom the previous value. Because the acoustic tends to vary gradually, thedifferential value will usually be a small number, thereby permitting the use of lessbits to represent the signal.Yet another feature of the present invention is the adaptability to a directdigital connection between the doctor's and the patient’s stations. Data is transmittedover the direct digital connection using an RS-232 interface.According to an aspect of the present invention, there is provided aadigitaltelephonic system for stethoscope signal processing wherein a patient and a doctorat a remote location are able to exchange actual stethoscopic auscultation soundsvia a plurality of analog and digital encoding and decoding means, said digitaltelephonic system comprising a patient station comprising a chest piece with astethoscope device; an amplifier; a low pass filter in direct communication with thechest piece; a Pulse Code Modulation (PCM) encoder and a UniversalAsynchronous Receiver/Transmitter (UART) in communication with each other andfurther in communication with said low pass filter; and a first modern connected to anoutput port of said UART; and a doctor station comprising means for receiving saidstethoscope sounds; a low pass filter connected to said means for receiving, a PCMdecoder in communication with said low pass filter on an output side and with arepeated byte device on an input side; a UART connected to said repeated bytedevice; and a second modem connected to said UART; said first modern at saidpatient station being connected to said second modem at said doctor station via atelephone line. 0According to another aspect of the present invention, there is provided amethod for converting, encoding and decoding analog and digital signals, whilemaintaining the quality and fidelity of auscultation sounds originating from astethoscope, to enable a patient at a patient station to transmit the sounds to adoctor at a remote doctor station comprising the steps of: amplifying analog signalsfrom a chest piece at said patient station; filtering said signals to get resultantCA 02265690 2004-06-224asignals; feeding said resultant signals to a PCM encoder to transform said analogsignals into a stream of binary data; transferring said stream of binary data to aUART and subsequently to a first modern; sending said binary data from said firstmodem to a telephone line; receiving said binary data from said telephone via asecond modem at said doctor station; transferring said binary data from said secondmodem to a UART and consequently to a repeated byte error handling circuit;decoding said binary signal to extract said analog signal via a PCM decoder; filteringsaid signal; and amplifying said signal to be received by a headset at said doctorstation.According to another aspect of the present invention, a method for converting,encoding and decoding analog and digital signals, while maintaining the quality andfidelity of auscultation sounds originating from a stethoscope, to enable a patient at apatient station to transmit the sounds to a doctor at a remote doctor stationcomprising the steps of: amplifying analog signals from a chest piece at said patientstation; filtering said signals to get resultant signals; feeding said resultant signals toa PCM encoder to transform said analog signals into a stream of binary data;transferring said stream of binary data to an UART and to an ADPCM encoder andsubsequently to a first modern; sending said binary data from said first modem to atelephone line; receiving said binary data from said telephone line via a secondmodem at said doctor station; transferring said binary data from said second modemto an UART and to a repeated byte error handling circuit; transferring said binarydata from said repeated byte error handling circuit to an ADPCM decoder; decodingsaid binary signal to extract said analog signal via a PCM decoder; filtering saidsignal; and amplifying said signal to be received by a headset at said doctor station.According to another aspect of the present invention, there is provided Amethod for converting, encoding and decoding analog and digital signals, whilemaintaining the quality and fidelity of auscultation sounds originating from astethoscope, to enable a patient at a patient station to transmit the sounds to adoctor at a remote doctor station comprising the steps of: amplifying analog signalsfrom a chest piece at said patient station; filtering said signals to get resultantsignals; feeding said resultant signals to a PCM encoder to transform said analogsignals into a stream of binary data; transferring said stream of binary data to aUART and subsequently to a first RS232; sending said binary data from said firstRS232 to a digital interface means; receiving said binary data from said first RS232CA 02265690 2004-06-224bvia a second RS232 at said doctor station; transferring said binary data from saidsecond RS232 to a UART and consequently to a repeated byte error handling circuit;decoding said binary signal to extract said analog signal via a PCM decoder; filteringsaid signal; and amplifying said signal to be received by a headset at said doctorstation.According to a further aspect of the present invention, a low bit rate digitaldevice for the transmission of stethoscope sounds from a patient at a location to adoctor at another location wherein an efficient coding scheme is used withoutsacrificing high linearity, the device comprising a patient station comprising a chestpiece comprising a stethoscope sensor, an amplifier, a lowpass filter in directcommunication with said chest piece; a PCM encoder and an UART incommunication with each other and further in communication with said low passfilter; and a first modern connected to an output port of said UART; and a doctorstation comprising means for receiving said stethoscope sounds; a low pass filterconnected to said means for receiving; a PCM decoder in communication with saidlow pass filter on an output side and with a repeated byte device on an input side; aUART connected to said repeated byte device; and a second modem connected tosaid UART; said first modem at said patient station being connected to said secondmodem at said doctor station via a telephone line.It will be appreciated that such features, methods and devices areadvancements over prior art methods and apparatus. Other features and advantagesof the present invention will become apparent upon examination of the followingdescription dealing with several specific embodiments thereof.BRIEF DESCRIPTION OF THEQRAWINGSFigure 1 is a block diagram showing the patient's and doctor’s stationsconnected via telephone line and associated digital signal processing systems.Figure 2 is an alternate embodiment in which and ADPCM encoder isused at both the patient’s and the doctor’s stations.‘Figure 3 is a block diagram of an alternate embodiment in which a directdigital connection is used between the patient’s and the doctor’s stations.CA 02265690 2004-06-224cQQTAILLED D§SCRlPT|ON OF THE PRELERRED EMBODIMENTThe present invention relates to an efficient coding scheme without sacrificinghigh linearity to digitally transmit high quality auscultationW0 98/117111015202530CA 02265690 l999-03- llPCT/US97/11394- 5 _sounds over normal telephone lines. Specifically, the present inventionprovides an improved coding system over existing practice in which linearencoding is used with wide bandwidth. Most of these encoders have topass the entire range of 300-3,0001-lz. The present invention passes onlyabout 50OHz.Referring now to Figure 1 a patient’s station 10 is connected to adoctor's station 12 as shown. Analog signal from chest piece 14 isamplified by amplifier 16 and fed to lowpass filter 18. The signal is thentransferred to PCM encoder 22. The output from PCM encoder 22 is sent tothe transmit side of Universal Asynchronous Receiver/Transmitter 24and then to modem or multiplexor 26. The signal is sent over telephoneline 28 to doctor's station 12. At doctor's station 12 the reverse processtakes place to convert the data signal back to audible sound. Thus, thesignal received by telephone line 28 is transferred into modem 32. Frommodem 32 it is transferred to UART 34. The output side of UART 34 isconnected to repeated byte 36. Repeated byte 36 is in turn connected toPCM decoder 38. The output from PCM decoder 38 is sent to lowpass filter42. The signal is then amplified by amplifier 44 and ultimately fed toheadset 46. -Figure 2 shows an alternate embodiment showing the addition ofAdaptive Differential Pulse Code Modulation (ADPCM) encoder 23 atpatient’s station 10 and ADPCM decoder 37 at doctor's station 12.Figure 3 shows yet another alternate embodiment in which thesignal is sent via direct digital connection 30. Modern or multiplexor 26 atpatient’s station 10 is replaced by RS232 data port 27. Further, modem ormultiplexor 32 at doctor's station 12 is replaced by RS232 data port 33.As will be discussed hereinbelow, some of the principal features ofthe present invention include use of a simple low pass filter to select onlythe bandwidth needed for the majority of auscultation sounds. Further,telephone standard Pulse Code Modulation (PCM) coding/ decoding isused to digitize the analog sounds from the stethoscope chest piece 14.PCM encoder 22 and PCM decoder 38 use a companding technique which,,.,.....-..-M.....»...~..m.».»....m................~._.....m.... . .. .. . .. .. ,.._._ ._........, .. . .. .W0 98/117111015202530CA 02265690 l999-03- llPCT/US97/11394- 6 -provides the equivalent of 12 bit resolution (per sample) with only 8 bits ofdata. No information is lost and quantization distortion is minimized inthis process. Furthermore, use of ADPCM encoder 23 and ADPCM decoder37 in addition to PCM encoder 22 and PCM decoder 38 cuts the bandwidthrequirements in half because only 4 bits are used instead of 8 bits for eachsample. Moreover, an asynchronous data communication technique isused to transfer the digitized voice samples. Typically, either synchronousor isochronous schemes are used for voice communications.Asynchronous communications is employed to keep the implementationsimple and low cost. Further, byte synchronization of the digitized voicesamples is easily achieved without having to add a frame synchronizationpattern. Additionally, a repeated byte technique is implemented to fill infor under run of data (missing bytes) and for data over run (extra bytes).Both situations can occur in an asynchronous communicationenvironment. Under run/ over run is the key reason asynchronouscommunication is not used for voice applications. The present inventionadvantageously utilizes precise but low cost clocks at both patient’s station10 and doctor's station 12. The under run/ over run occurs infrequently,and with the repeated byte technique is not detectable by the typical humanear.Considering Figures 1-3 in more detail, the present inventionprovides digital techniques for transmission of auscultation data such thathigh quality sound is transported at low cost over a relatively smallbandwidth. Thus, narrow bandwidth data transmission channels areefficiently and advantageously utilized.As shown in Figures 1-3, the digital telephonic system of the presentinvention includes patient’s station 10 and doctor's station 12. In thepreferred embodiment, patient’s station 10 includes chest piece 14. Chestpiece _14 includes a stethoscope sensor with an embedded microphoneattached to an electronic module. The analog signal from chest piece 14 isamplified by amplifier 16 and then filtered by low pass filter 18. Theresulting signal is fed to PCM encoder 22. The analog stethoscope signalsW0 98/117111015202530CA 02265690 l999-03- llPCT/US97/11394_ 7 _are transformed into a stream of binary data by PCM encoder 22.Subsequently, UART 22 and modem or multiplexor 26 send the binarydata over telephone line 28 to modem 32 and UART 34. The signal is sentthrough repeated byte 36. As will be discussed hereinbelow, repeated byte36 includes error handling circuit. Error control is optional and isimplemented using a parity bit per each 8-bit PCM sample. After sendingthe data through repeated byte 36, PCM decoder 38 translates the binarydata into analog signals which are presented to the doctor via headset 46.Good quality transmission over low bit rate data channels isachieved by employing a number of techniques. First, only a smallnumber of quantization levels (e.g., 256) are used for PCM decoder 38thereby requiring a small number of data bits for example 8 bits. Tocompensate for the small number of bits, a companding procedure is usedto minimize the amount of quantization noise by using smaller steps forlow amplitude signals and larger steps for high amplitude signals. Withthe PCM companding, it is possible to effectively provide 12-bit codingresolution with only 8 bits. Further, optional error handling isimplemented so that no bandwidth is used for retransmitting corrupteddata. In one embodiment error checking is done by transmitting a paritybit with the data. When an error is detected at the receiving end, thecorrupted byte is discarded, and no attempt is made to retransmit thecorrupted byte. Instead, the corrupted byte is replaced with the byteoccurring just prior to the corrupted byte. The result is that the same byteis used twice which is a reasonable error-correcting procedure. Further,digital data is transmitted asynchronously rather than synchronously.This keeps the implementation simple and cost effective.A second embodiment, shown in Figure 2 uses an adaptivedifferential PCM (ADPCM) encoder.value of each byte into a differential value which represents the increaseThis enables the translation of theor decrease from the previous value. Because the acoustic signal tends tovary slowly, the differential value will usually be a small number, therebypermitting the use of less bits to represent the signal.WO 98/117111015202530CA 02265690 l999-03- llPCT/U S97/ 11394_ 8 _A third embodiment shown in Figure 3 is similar to that of Figure 1,except that the telephone line is replaced with a direct digital connection.Data is transmitted over this direct connection using RS-232 27 and 33interface.Under normal operation where a modem is used as the interface,patient station 10 communicates with doctor's station 12 in the followingmanner. Either the patient or the doctor initiates contact by calling theremote station in the manner outlined in commonly-owned co—pendingPatent Application entitled ”Single—Line Telephonic System For Multi-Signal Processing, filed on July 11, 1996 and assigned Serial Number08/679,649, the specification and drawings of which are incorporatedherein by reference. In an alternate arrangement where a multiplexor isused as an interface, a high-end video conferrencing equipment currentlyin use in hospitals includes digital channels which could be modified toincorporate audio and video in the same line. Such arrangements andconfigurations will enable patient-doctor communications. Once thecommunication is established, the patient may apply chest piece 14 tohis / her chest to enable the doctor to monitor and provide diagnosis basedon the auscultation sounds transmitted from patient station 10 to thedoctor's station 12 via telephone line 28 or digital connection 30. Thedoctor listens through headset 46. More significantly, the presentinvention utilizes a digital-based stethoscope to send stethoscope soundsfrom the patient over a data communication channel to a doctor. Thelowest known digital Stethoscopes are 32Kb of bandwidth. Thuscommunications implementing current stethoscopes in the normal homephone is almost impossible to be used for the purposes outlined in thepresent invention.Accordingly, the digital telephonic stethoscope system of the presentinvention is intended to be used as a stand-alone piece of equipment ormay be integrated with other Telemedicine Systems (TS). Typically, thedigital telephonic system of the present invention will be a part of atelemedicine system where a multi-channel data communication link hasW0 98/117111015202530CA 02265690 l999-03- llPCT/US97/11394- 9 -been established. The digital telephonic system is generally connected toone of modems 26 and 32 or RS232 27 and 33 wherein the RS232 unit asdescribed in this application is indicative of a multiplexor with an RS232interface which is equivalent to a Data Communication Equipment (DCE).The patient’s station 10 and the doctor's station 12 are basically ”ON”LEDs labeled STETH at both stations show that the unit ispowered. Under normal operation, station 10 will send out a data streamall the time.of digitally encoded auscultation sounds. This signal is received by station12 whenever the digital telephonic system data channel is up. The signaltransmission and reception units of stations 10 and 12 automaticallysynchronize.The digitization process includes filtering the analog signal to below500 Hz, for example 450Hz and encoding and decoding using PCM 22 and38 and optional ADPCM 22 and 37 with a low sampling rate of for example1,250 samples per second.In the preferred embodiments disclosed hereinabove, asynchronousdata communications protocol is used with preferably one start bit, oneparity bit and one and half stop bits. The asynchronous transmission withUART 24 and 34 preferably uses a parity bit (optional) to protect againstsingle bit errors. When an error is detected, the byte is discarded and theprevious byte is repeated. Similarly, the repeated byte technique is alsoused to fill in for under-run of data and to discard extra bytes due to dataover-run. Local oscillator (not shown) at both stations 10 and 12 preferablyinclude +/-100 ppm accuracy.While the preferred embodiments of the invention have beenshown and described, it will be obvious to those skilled in the art thatchanges, variations and modifications may be made therein withoutdeparting from the invention in its broader aspects and, therefore, the aimin the appended claims is to cover such changes and modifications as fallwithin the scope and spirit of the invention.

Claims (22)

What is claimed is:

1. A digital telephonic system for stethoscope signal processing wherein a patient and a doctor at a remote location are able to exchange actual stethoscopic auscultation sounds via a plurality of analog and digital encoding and decoding means, said digital telephonic system comprising a patient station comprising a chest piece with a stethoscope device; an amplifier; a low pass filter in direct communication with the chest piece; a Pulse Code Modulation (PCM) encoder and a Universal Asynchronous Receiver/Transmitter (UART) in communication with each other and further in communication with said low pass filter; and a first modem connected to an output port of said UART; and a doctor station comprising means for receiving said stethoscope sounds; a low pass filter connected to said means for receiving, a PCM decoder in communication with said low pass filter on an output side and with a repeated byte device on an input side; a UART connected to said repeated byte device; and a second modem connected to said UART; said first modem at said patient station being connected to said second modem at said doctor station via a telephone line.

2. The digital telephonic system of claim 1 wherein said plurality of analog and digital encoding and decoding means comprise direct digital interface means.

3. The digital telephonic system of claim 1 or 2 wherein said plurality of analog and digital encoding and decoding means comprise said chest piece connected to a low pass filter and to a PCM encoder wherein said PCM encoder comprises connections to a UART on an output side and further said UART
comprises connections to a first modem; and said receiver means connected to a low pass filter and to a PCM decoder and further comprises connections to a repeated byte circuit means and a UART comprising connections to a second modem; said first modem and said second modem comprising operable connections via a telephone line to transmit said signal from the patient station to the doctor station.

4. The digital telephonic system of claim 3 wherein said repeated byte circuit means comprises an error handling system.

5. The digital telephonic system of claim 1 wherein said plurality of analog and digital encoding and decoding means comprise said chest piece connected to a low pass filter and to a PCM encoder and an Adaptive Differential Pulse Code Modulation (ADPCM) encoder wherein said PCM and said ADPCM
encoder comprise connections to a UART on an output side and further said DART comprises connections to a first modem; and said means for receiving being connected to a low pass filter and to a PCM decoder, an ADPCM decoder and further comprises connections to a repeated byte circuit means and a UART
wherein said UART comprises connections to a second modem; said first modem and said second modem having operable connections via the telephone line to transmit said signal from the patient station to the doctor station.

6. The digital telephonic system of claim 3 wherein said repeated byte circuit means comprises an error handling system.

7. The digital telephonic system of claim 2 wherein said direct digital interface means comprises input and output ports having connections to RS232 units on both said input and output ports.

8. The digital system of claim 2 wherein said plurality of analog and digital encoding and decoding means comprise said chest piece connected to a low pass filter and to a PCM encoder wherein said PCM encoder comprises connections to a UART on an output side and further said DART comprises connections to a first RS232 unit; and said receiver means connected to a low pass filter and to a PCM decoder and further comprising connections to a repeated byte circuit means and a UART comprising connections to a second RS232 unit; wherein said first RS232 unit and said second RS232 unit comprise operable connections via said direct digital interface means to transmit said signal from the patient station to the doctor station.

9. The digital telephonic system of claim 8 wherein said repeated byte circuit means comprises an error handling system.

10. A method for converting, encoding and decoding analog and digital signals, while maintaining the quality and fidelity of auscultation sounds originating from a stethoscope, to enable a patient at a patient station to transmit the sounds to a doctor at a remote doctor station comprising the steps of:
amplifying analog signals from a chest piece at said patient station;
filtering said signals to get resultant signals; feeding said resultant signals to a PCM
encoder to transform said analog signals into a stream of binary data; transferring said stream of binary data to a UART and subsequently to a first modem; sending said binary data from said first modem to a telephone line; receiving said binary data from said telephone via a second modem at said doctor station;
transferring said binary data from said second modem to a UART and consequently to a repeated byte error handling circuit; decoding said binary signal to extract said analog signal via a PCM decoder; filtering said signal; and amplifying said signal to be received by a headset at said doctor station.

11. The method of claim 10 wherein said stream of binary data is directed through an ADPCM encoder subsequent to passing through said PCM.

12. The method of claim 10 wherein said step of decoding comprises a step of error checking by transmitting a parity bit with said binary data.

13. The method of claim 10 wherein said digital signals are transmitted asynchronously.

14. A method for converting, encoding and decoding analog and digital signals, while maintaining the quality and fidelity of auscultation sounds originating from a stethoscope, to enable a patient at a patient station to transmit the sounds to a doctor at a remote doctor station comprising the steps of:
amplifying analog signals from a chest piece at said patient station;
filtering said signals to get resultant signals; feeding said resultant signals to a PCM
encoder to transform said analog signals into a stream of binary data; transferring said stream of binary data to a UART and to an ADPCM encoder and subsequently to a first modem; sending said binary data from said first modem to a telephone line; receiving said binary data from said telephone line via a second modem at said doctor station; transferring said binary data from said second modem to a UART and to a repeated byte error handling circuit; transferring said binary data from said repeated byte error handling circuit to an ADPCM decoder; decoding said binary signal to extract said analog signal via a PCM decoder; filtering said signal; and amplifying said signal to be received by a headset at said doctor station.

15. A method for converting, encoding and decoding analog and digital signals, while maintaining the quality and fidelity of auscultation sounds originating from a stethoscope, to enable a patient at a patient station to transmit the sounds to a doctor at a remote doctor station comprising the steps of:
amplifying analog signals from a chest piece at said patient station;
filtering said signals to get resultant signals; feeding said resultant signals to a PCM
encoder to transform said analog signals into a stream of binary data; transferring said stream of binary data to a UART and subsequently to a first RS232; sending said binary data from said first RS232 to a digital interface means; receiving said binary data from said first RS232 via a second RS232 at said doctor station;
transferring said binary data from said second RS232 to a UART and consequently to a repeated byte error handling circuit; decoding said binary signal to extract said analog signal via a PCM decoder; filtering said signal;
and amplifying said signal to be received by a headset at said doctor station.

16. The method of claim 15 wherein said repeated byte circuit means further comprises an error checking step to insure that no bandwidth is used for retransmitting corrupted data.

17. The method of claim 16 wherein said error checking step further comprises transmitting a parity bit with said binary data.

18. The method of claim 15 wherein an error correction procedure is implemented comprising the steps of: transmitting a parity bit with said binary signal; detecting an error at the receiving end to identify corrupted byte;
discarding said corrupted byte when detected; and replacing said corrupted byte with a byte occurring just prior to said corrupted byte.

19. The method of claim 18 wherein said PCM decoder receives said byte occurring just prior to said corrupted byte twice as part of said error correction procedure.

20. A low bit rate digital device for the transmission of stethoscope sounds from a patient at a location to a doctor at another location wherein an efficient coding scheme is used without sacrificing high linearity, the device comprising a patient station comprising a chest piece comprising a stethoscope sensor; an amplifier; a low pass filter in direct communication with said chest piece; a PCM
encoder and a UART in communication with each other and further in communication with said low pass filter; and a first modem connected to an output port of said UART; and a doctor station comprising means for receiving said stethoscope sounds; a low pass filter connected to said means for receiving; a PCM decoder in communication with said low pass filter on an output side and with a repeated byte device on an input side; a UART connected to said repeated byte device; and a second modem connected to said UART;
said first modem at said patient station being connected to said second modem at said doctor station via a telephone line.

21. The device of claim 20 wherein an ADPCM encoder provides connection between said PCM encoder and said UART at said patient station and an ADPCM decoder provides connection between said PCM decoder and said repeated byte device at said doctor station.

22. The device of claim 20 wherein said first modem at said patient station is replaced by an RS232 and said second modem at said doctor station is replaced by an RS232 and wherein said telephone line is replaced by a digital interface.