Types of Stethoscopes Currently Available
In today’s market, there are three general types of stethoscopes available to consumers: the traditional acoustic, amplifying, and digitizing. All of the electronic stethoscopes fall into two broad categories; amplifying and digitizing.
Traditional Acoustic
Stethoscope (from the Greek stethos-chest and skope-examination) is an acoustic medical device for auscultation, or listening to the internal sounds of a body. The stethoscope was invented in France in 1816 by Rene Laennec. It consisted of a wooden tube and was monoaural, which meant you could only hear through one ear when utilizing it. Prior to Laennec’s invention, physicians would perform “direct auscultation” to listen to patient’s internal sounds, which consisted of placing their ear directly on the patient’s body. In 1851 Arthur Leard invented the binaural stethoscope, which most closely resembled the traditional acoustic device as we know it today. The function of the acoustic stethoscope is attributed to three main components discussed further below. The components are:
Chest Piece
The acoustic stethoscope operates on the transmission of sound from the chest piece, via air-filled hollow tubes, to the listener’s ears. The chest piece usually consists of two parts that can be placed against the patient for sensing sound: the bell (hollow cup) and the diaphragm (disc). The bell transmits lower frequency sounds, while the diaphragm transmits higher frequency sounds. When the bell is placed on the patient, the vibrations of the skin directly produce acoustic pressure waves that travel to the listener’s ear. When the diaphragm is placed against the patient’s skin, body sounds vibrate the diaphragm, creating acoustic pressure waves which then travel to the listener’s ears. The human body then translates these pressure waves into sound and allows the listener to “hear” what they are examining.
With advances in acoustic stethoscope design, various companies have also come up with newer single-head chest piece designs, otherwise known as “dual frequency” or “tunable” diaphragms. These newer diaphragms have a one-sided chest piece and rely on user-applied pressure to change between bell and diaphragm modes. For low-frequency sounds (bell mode), light contact is used on the chest piece. The diaphragm membrane is then contained by a flexible surround that actually suspends it, allowing for the traditional functionality and sound transfer of the bell. For high-frequency sounds (diaphragm mode), firm contact pressure is used on the chest piece. By pressing on the chest piece, the diaphragm membrane moves inward until it reaches an internal ring. The ring simply restricts the diaphragm membrane’s movement and allows for the traditional functionality and sound transfer mechanism of the diaphragm.
Tubing
Stethoscope tubing is the air-filled hollow tubing that allows sound energy to be transmitted from the chest piece to the clinician. Tubing can vary by manufacturer and comes in different varieties; many are now latex free. There are single-lumen tubes which are usually split into two tubes at the ear pieces, bi-lumen tubes that consist of two internal lumen incorporated into a single lumen design, and tubing systems that consist of two separate tubes that are directly connected from chest piece to each ear piece. Each type of stethoscope tubing has its own resonant frequency which depends on the length and internal width of the tubing, similar to a pipe organ. (Finkelstein, 2008) Thicker tubing can better insulate the sound being transmitted against outside distortion. An increase in the length of the tubing will decrease the pressure at the end of the tubing as a result of frictional and other internal forces. The overall change in length between most stethoscope tubing is relatively small. Therefore, the decrease in acoustic pressure is generally not thought to be detectable by the human ear. As tubing length increases, resonant frequency decreases and sounds have greater potential to be attenuated. Tubing length tends to come down to preference, but is usually between 18-26 inches.
Ear Pieces
When a Clinician places the stethoscope chest piece on a patient, they are closing a circuit that allows sound energy to travel internally from the patient, through a conductor (the stethoscope), and to the listener. In this type of circuit, a break or air leak in the circuitry may result in decreased sound quality or completely block the transmission of sound. The physical connection that is made between the ear tips and the human ear is very important. The insertion pressure, ear tip seal, and ear tip insertion angle are all variables that can affect this connection. Some manufactures offer hard and soft sealing ear tips, various sizes of ear tips to accommodate ear canal size. These give the user the ability to adjust the insertion pressure and angle by manually manipulating the head set. When using an acoustic stethoscope, it is important that the ear pieces angle forward to fit most naturally into the external ear opening.
Electronic Stethoscopes
One problem with acoustic stethoscopes is that the sound level is extremely low. Electronic stethoscopes utilize advanced technology to overcome these low sound levels by electronically amplifying body sounds. Electronic stethoscopes require conversion of acoustic sound waves obtained through the chest piece into electronic signals which are then transmitted through uniquely designed circuitry and processed for optimal listening. The circuitry consists of components that allow the energy to be amplified and optimized for listening at various frequencies. The circuitry also allows the sound energy to be digitized, encoded and decoded, to have the ambient noise reduced or eliminated, and sent through speakers or headphones.
Unlike acoustic stethoscopes, which are all based on the same physics, transducers in electronic stethoscopes vary widely. The simplest and least effective method of sound detection is achieved by placing a microphone in the chest piece. This method suffers from ambient noise interference. Another method comprises placement of a piezoelectric crystal at the head of a metal shaft, the bottom of the shaft making contact with a diaphragm. Some manufacturers use a piezoelectric crystal placed within foam behind a thick rubber-like diaphragm. Another manufacturer uses an electromagnetic diaphragm with a conductive inner surface to form a capacitive sensor. This diaphragm responds to sound waves identically to a conventional acoustic stethoscope, with changes in an electric field replacing changes in air pressure. This preserves the sound of an acoustic stethoscope with the benefits of amplification. No matter what type of sophisticated circuitry or transducer is utilized, practitioners need to be prepared for a difference in the sound quality between acoustic and electronic stethoscopes. Clinicians will automatically recognize an “electronic” quality to even the best sounds obtained from the electronic stethoscopes currently on the market. Utilizing electronic stethoscopes for auscultation definitely takes getting used to, but with repeated exposure any practitioner can learn to appreciate the sound obtained with an electronic stethoscope.
The fact that sounds are transmitted electronically allows electronic stethoscopes to offer features such as audio or serial data output, wireless transmission, and recording of sound clips.
Amplifying Stethoscopes
The majority of the electronic stethoscopes on the market have an audio output signal that, through the use of a stereo and/or mono cable connection, can allow the audio output collected by the stethoscope to be transmitted real time to an accompanying software application. The accompanying software may employ various algorithms that are developed for interpretation and diagnosis of the audio output obtained from the electronic stethoscopes. Audio output processed through various accompanying software packages can be saved as files and then transmitted via email and various other communication methods for asynchronous assessment and diagnosis. Some electronic stethoscopes that have audio data output options can also be hooked up to a videoconferencing unit’s audio input, which would enable them to send the sound data real time over a network connection to another videoconferencing endpoint. The videoconferencing units would act as a decoders and encoders of the sound data, allowing it to be transmitted over a network. In this type of setup, the user needs to be mindful of the fact that generally the sound data can only be sent between like brands of videoconferencing units and sometimes as specific as like models of like brands. Depending on the speakers at the other end of the videoconference, some of the frequencies obtained may not be discernable, and the audio output quality has the potential to suffer. This adjunct to the videoconferencing session may also utilize additional bandwidth, causing the quality of the video session to suffer as well. Additionally, if the video participants wish to speak to each other during the session, the users may have to set up a means to also allow this communication to occur because only one type of audio transmission may be allowed at a time. Some electronic stethoscopes allow transmission of data through a wireless or Bluetooth interface to other devices. Most of the wireless electronic stethoscopes require dongles (Bluetooth receivers) to transmit data wirelessly. Wireless and Bluetooth data communication strategies utilize more recent technologies. However, this form of data transmission may be a limiting factor in compatibility with devices other than computers; videoconferencing units for example.
Only one stethoscope currently on the market allows for onboard recording and playback directly into the physical portion of the stethoscope. Any electronic stethoscope that has data transmission and a software interface will allow for recording of clips that are not stored locally on the device. Some of the electronic stethoscopes offer visual output of the heart rate and EKG waves detected directly on the device and all allow for visual output of the sound waves collected in conjunction with their accompanying software packages.
Digitizing Stethoscopes
A few of the electronic stethoscopes on the market are called “digitizing stethoscopes” because they convert the audio sound to a digital signal. These stethoscopes can transmit serialized audio data that can be shared real time (synchronously) and/or in a store and forward fashion (asynchronously). These units work by detecting sound through the electronic stethoscope sensor, converting that sound energy to electricity and running it through circuitry which can amplify it, filter it by frequency, and finally convert the data from analog to a digital. Click here to learn more about digital to analog conversion. Basically, the units themselves are codecs that digitally encode and decode data so it can be transmitted over a network. After the data is digitized, it can be sent through a videoconferencing unit through its RS32 input across a network or through computer software with a serial TCP/IP converter and across a network. One stethoscope can transmit the digital data using USB to store-and-forward software. Both types of data transmission require that there is a corresponding electronic stethoscope unit on the other side that will convert the digital signal back to an analog signal, amplify the sound, filter the sound frequency, and transmit the sound energy to the human ear.
Functions and Features
Electronic stethoscope design can be any number of variations on the traditional acoustic stethoscope design.
Power
Amplifying Stethoscopes
All of the electronic stethoscopes require some degree of power to run the circuitry components that allow their features to function. The types of power required may vary, but are generally batteries (AA, AAA, Lithium or rechargeable). Some of the stethoscopes offer visual indicators of the power level for the user to see on an LCD screen or may have an LED indicator on the chest piece or stethoscope module itself. Most have some type of audio or visual signal to the user when the power level is running low, which is necessary because most will not function without adequate power supply. The majority have a power button or switch that can be located on the chest piece, on a module incorporated in the tubing, or directly on the stethoscope module itself.
Digitizing Stethoscopes
These stethoscopes utilize AC 120 V power cords rather than batteries. They do have a light that indicates they are powered on. The two digitizing units on the market have no internal power supply and no on/off switching capability other than plugging and unplugging the units.
Auto-Shutoff
Amplifying Stethoscopes
Power consumption and battery life preservation are important features in the electronic stethoscope, which in general don’t work unless there is a power supply. Therefore, most of the electronic stethoscopes on the market allow for some degree of auto-shutoff as a power saving feature. The auto-shutoff time period can vary in length and in some models can allow for customization of the time period. For convenience and time saving, we found it to be most convenient when a “settings retained” feature was paired with an auto-shutoff feature. The retained settings functionality was extremely important in the units that had a set run time, at least when the unit was repowered the user could return to use in a relatively fast manor. We also found it more useful when an auto-shutoff period starts after the last button push or sound detected, as opposed to a set time interval. Models that have a set auto-shut off period, and in essence a set run-time despite current usage, were inconvenient and risked the unit turning off during a patient examination.
Digitizing Stethoscopes
These units utilize AC power and do not have auto-shut off and do not employ any power saving features. As they do not have batteries, digitizing stethoscopes do not have the same need to automatically turn off. The digitizing stethoscopes will never turn off mid-examination. If the plug should come unplugged during an examination, the user will know automatically because the sound will stop transmitting and the LED indicator will turn off.
Volume Control & Amplification
Electronic stethoscopes take the collected acoustic sound energy from the chest piece and convert it into electrical energy. As the converted voltage is sent through the electronic stethoscope’s internal circuitry, it encounters an amplifier component. This amplifier has the ability to take in small amounts of energy and convert the signal to increase the sound output. The majority of the electronic stethoscope units have volume buttons or a volume dial. It can be located on the chest piece, on a module incorporated in the tubing, or directly on the stethoscope module itself. Some of the modules offer a visual or audio indicator of the volume level currently in use, while others do not.
In some models amplification can be turned on and off. Some models incorporate the amplification process as a part of increasing or decreasing the unit’s volume, while in other models it is a separate function. As amplification level increases so does volume level. In general, we found more ease of use for the user in the units where amplification and volume increase/decrease buttons were a combined process. The single process allows for one less variable when the user is attempting to assess a patient. Manufacturers offer varying degrees of sound amplification, most commonly they claim sounds are 10-50 times amplified.
A current shortcoming that we noted with the electronic stethoscopes is that movement of the chest piece on clothing or skin surfaces may produce painful sound artifact. Care must be taken when placing the chest piece or moving the chest piece to avoid abrupt changes in sound and/or volume level. A feature that we would love to see in the future would be some sort of sound limiting mechanism that blocks sudden increase in sounds, perhaps at certain frequencies or decibel levels.
Chest Piece
Most stethoscopes will typically have some sort of button or switch to electronically switch between frequency filtering (listening modes). Some electronic stethoscope chest piece may also utilize a tunable diaphragm or may require physical changing of the bell and the diaphragm. This switching of modes is simply filtering the frequency being heard, which is explained further in the frequency section. There is one model of electronic stethoscope on the market that requires the user to plug and unplug the chest piece module from the stethoscope unit to change between transmit and receive modes.
Tubing
Electronic stethoscope tubing is remarkably similar to acoustic stethoscope tubing in general; however there are some notable variations. Some models incorporate modules that are mounted in or around the tubing, where the circuitry for the sound conversion is located. The basic principles of tubing length and thickness are the same in electronic stethoscope as they are in acoustic stethoscopes. Other models’ tubing may internally contain additional circuitry and transducers for sound conversion. Some models do not use a traditional tubing design at all, opting instead for electronic cords.
Ear Tips
Ear tip designs in electronic stethoscopes often utilize the same principles as their acoustic counterparts; however, some stethoscope designs are significantly different. The most outstanding difference is that some models of electronic stethoscope do not even contain ear tips. Some of the electronic stethoscopes allow the user to use headphones. It is important to note on this topic that most of the headphones included with the stethoscopes currently on the market have sub-optimal sound quality. This is especially true for the “ear bud” style of headsets that are inserted into the ear.
The investment in a quality pair of headphones goes a long way to significantly improved sound output quality. For all of our testing, we utilized the full-sized, professional-quality R80 stereophones by Koss. These headphones have a frequency response of 16-20,000Hz, a 60 Ohm impedance level, and a less than a 0.2% distortion rating. We found that the models of stethoscopes that utilized headphones mostly allowed for interchangeability, however there was one stethoscope manufacturer that did not. That manufacturer did offer two models of Koss headphones for purchase; however they had customized cabling that make it necessary to purchase the headphones directly from them.
For the models that utilized ear tips, in general they offered additional sizing and replacement options with a variety of types of ear tips. The ear tips ranged from silicone soft sealing to molded plastic. There was one model that had built in functionality in the tubing to tighten ear tip insertion pressure.
Frequency
The full range of human hearing extends from 20-20000 Hz. The accepted frequency range of human heart sounds is about 20-200Hz and the accepted frequency range of human lung sounds is about 25-1500Hz. Most of the electronic stethoscopes on the market offer Bell mode, Diaphragm Mode and an Extended Range mode. Extended Range is usually referred to as wide, extended, or organ mode. For the most part, each electronic stethoscope has a button or switch to change between modes. The button or switch for changing frequency or mode can be located on the chest piece, on a module incorporated in the tubing, or directly on the stethoscope unit itself.
When the stethoscopes are placed in these modes they have two potential behaviors, they either block out all sounds except for the defined frequency range or they allow all frequency ranges through but optimize the sounds in a defined frequency range. For the stethoscopes that we analyzed there was variety in the frequency ranges of the bell, diaphragm and extended modes, but in general bell mode was from 20-650Hz, diaphragm mode was from 20-2000Hz, and the extended range was from 20-1500Hz. The overall sampling frequency range on the evaluated stethoscopes was from 15-20000Hz. See each individual cut sheet for the specific unit frequency ranges reported by each manufacturer.
Ambient Noise Reduction
Ambient noise enters the stethoscope both through the air and through the patient’s body. Ambient noise can passively be reduced through the principles of ear tip insertion pressure, ear tip seal, ear tip insertion angle and good stethoscope design. However, in the case of active ambient noise reduction, the ambient noise is canceled using technology. This technology utilized is a noise canceling component in the circuitry that the sound energy passes through. Once ambient noise is generated, it is recorded by the microphone. The microphone is connected to the noise-canceling circuit. The noise-canceling circuit then uses the wave property of sound to cancel the ambient noise. It generates waves (inverse signals) that are exactly opposite to the incoming waves of the ambient noise effectively canceling them. Each manufacturer has a slightly different proprietary mechanism for canceling out incoming ambient noise. We found the level of sound canceled to vary by manufacturer. In general, quieter environments allowed for better quality sound to be obtained despite this technologies presence.
Physics of Sound
A sound is, roughly speaking, the motion of waves of alternative pressure generated by a vibrating object. This vibrating source sets particles in motion and in the case of a sound with only one tone, the individual particles moves around their resting point, with the same frequency of that tone. In each movement, vibrating particles push nearby ones, putting them in motion, and therefore creating a chain effect generating areas of high and low pressure. This alternation between low and high pressure areas moves away from the sound source and so does the sound wave. Usually those waves can be detected by their mechanical effect on a membrane (it could be a microphone’s membrane or a stethoscope’s diaphragm, etc.). For a real world example: say there is a trumpet playing in the room. The vibrating air coming from the horn moves the air in that room causing your ear drums to vibrate back and forth along with the vibration of air molecules. You would experience these vibrations as sound.
Analog and Digital Conversion Explained
Now say there is a microphone in the room. A trumpet is played and vibrates the air around it, setting up a series of pressure changes that radiate through the air in the room. When these pressure changes reach the microphone’s diaphragm, it shakes back and forth with the vibrations, much like your ear drum. The microphone “hears” these vibrations and converts them into electrical voltages that are an “analogy” of the air pressure changes that made the original sounds. The analog audio voltage fluctuations are fed through a circuit component called the analog to digital convertor, which changes the incoming voltages to digital snapshots 44,100 times a second, assuming a 44.1KHz digital sampling rate. Each snapshot consists of 16 zeros and/or ones, or 16 bits. Each combination of zeros and/or ones represents a different signal voltage. Some say that capturing audio with 16 bits 44,100 times a second may not be enough to accurately describe what our ears can hear; some later HD versions now capture at 24bits 192,000 times per second.
When we want to actually hear digital audio, the audio data has to go through a digital to analog convertor, which changes the binary (zeros and/or ones) code samples to analog voltage fluctuations that are then sent to a power amplifier and on to speakers. The speakers shake the air molecules in our listening room enough for us to hear a reasonably accurate reproduction of the original sound.
Audio Input to the Computer Explained
A typical stereo soundcard has a pair of analog to digital converters and a pair of digital to analog converters. The LINE IN of the soundcard is an analog input, and the LINE OUT is an analog output. The converters are on the soundcard itself. The analog audio comes in the LINE IN of the soundcard and is digitized in the soundcard’s analog to digital convertor. The audio data travels through the PCI bus to the CPU and is then stored on the hard drive as a digital audio file, typically .WAV on a PC. The audio is now in binary (digital) form, called “digital audio data.” To play back the digital audio file, the CPU sends the audio data through the PCI bus to the soundcard, where its digital to audio converter converts the audio to analog voltages and sends it out through the LINE OUT jack.
Use Potentials
Electronic stethoscopes have great use potential in telemedicine programs. Electronic stethoscopes can take the physical assessment process, a traditionally face-to-face encounter, and enable it to take place over great distances. This is pretty remarkable, considering that just about 150 years ago medical practitioners had to place their ear directly on their patient’s body to do a physical assessment.
There are three basic ways the electronic stethoscopes currently on the market can be used. They can be used at the bedside as standalone amplifying stethoscopes; they can be used in conjunction with a software program to send audio clips asynchronously or in a store and forward fashion; they can be used to transmit auscultation data real time over videoconferencing networking, or by a direct network connection to one another.
Store and Forward (Asynchronously)
Through varying methods, the electronic stethoscopes currently on the market can work in conjunction with their accompanying software programs to transmit auscultation data to additional providers in a store and forward fashion. In store and forward data transmission, practitioners can capture audio during a patient assessment and then store the clips on their computer system. Sound files are stored in various formats based on the stethoscope and include: .wav, etc. Once these sound files are stored, a practitioner has many options for what to do with the data. A practitioner can simply store the data in a secure fashion and use it as a digital record of their auscultation, which can be especially useful when trying to follow a progressive condition or simply to compare auscultations from visit to visit or year to year. If a suspected pathology is auscultated during physical exam a practitioner may also save the clip and decide to send it to a colleague or specialist for consultation at a later time.
Stethoscope Software
Manufacturers of amplifying stethoscopes team with software companies to provide an auscultation & sound capture solution. Most of these capture the sound from an amplifying stethoscope and save it as some electronic format, most commonly .wav. Each of the software programs currently on the market has slightly different functionality when it comes to capture, analysis, export, and sending and receiving of store and forward electronic stethoscope clips. In general, most programs are able to export files in a proprietary file format or .WAV file format that can then be emailed to another user and played back. Typically, the consultant needs to also have a copy of the software installed on their system in order to maximize functionality.
Most of these software programs state that their software can be used for telemedicine because a file can be exported and sent by email. A user can simply email the non-proprietary .WAV formatted file to another user, which most users with a free media player can play back on their system. .WAV formatted files will lack any data about the patient or the ability for the sound to be frequency filtered or any other software features to be utilized. In general when sending these files, a user will attach them to an email and send them over some sort of network connection. On a cautionary note, users must ensure that a secure means of sending patient data over a network is employed to protect patient confidentiality with any files being transmitted.
No matter how the data is transmitted or even if the files are stored locally on the users system, the playback sound quality is subject to the user’s individual sound settings, soundcard and speaker type. Some frequency ranges may not be able to be played back on various sound configurations which can greatly affect sound quality perception. It is important to know the playback abilities of your system to optimize sounds played back. Possibly an investment in a higher quality soundcard and/or speakers with a wider frequency range may go a long way towards playing back diagnostic quality sound clips. This becomes especially important on the consultant side of a store and forward consultation.
At least two software programs work with specific stethoscopes that directly integrate a file format that can be saved, archived, or sent as a telemedicine case. One of the software programs is specifically for stethoscope use and the other software is for multiple biomedical peripherals. Digitizing stethoscopes require identical hardware at the sending and receiving end to code and decode the signal. This method of transmission provides the best preservation of sound quality.
Sending auscultations in a store and forward fashion is an efficient means of utilizing practitioner time, as the work efforts are asynchronous; the sound clip can be reviewed at an available time and does not require the patient and the provider in the room at the same time. In general consultants are able to review a case and clips and get a response back to colleagues in a much faster time period than it takes to get a patient into another practitioner’s office for consultation.
Real Time (Synchronously)
The other use potential for utilizing electronic stethoscopes is real time transmission of data, with the patient in one location and the practitioner simultaneously in another location. This transmission setup has the traditional time constraints of scheduling an appointment and the live dynamics between practitioners and patients; but allows for instantaneous feedback and interaction. This method of data transmission has additional potential network connectivity issues related to making network connections. Considerations must be made for potentially more bandwidth consumption when adjuncts to videoconferencing are utilized, so the sound and video quality are not adversely affected.
The electronic stethoscopes currently on the market allow for real time use by three basic methodologies: over a live network connection utilizing a software configuration and device to device communication, using a videoconferencing units RS 232 data input to communicate with another videoconferencing unit over a network, or by using a videoconferencing unit as a codec with the audio output of the electronic stethoscope channeled through the audio input on a videoconferencing unit communicating over a network to another videoconferencing unit.
Summary
There are currently only three electronic stethoscope models that can be utilized to transmit serial data for real time transmission: the Littmann 3200, the Telehealth Technologies TR1-EF, and the CareTone. These models of electronic stethoscopes, which we collectively refer to as digitizing, have serial data transmission as opposed to audio only data transmission. Any number of potential real time connection configurations can be made with the digitizing stethoscopes, the type that best suits your Telehealth program can be determined with a thorough and accurate needs assessment.
Most amplifying stethoscopes can be attached to the audio in jack of a videoconferencing unit to communicate over a network to another videoconferencing unit. This method of transmission relies on the videoconferencing codec for sound quality and transmission. Users have had various degrees of success using this methodology. To maximize sound quality, the same make and model of videoconferencing units with high quality sound codec must be employed.
There are pros, cons, and special considerations for each type of data transmission. All of these potential variances and variables may impact the quality of the data transmitted and received, and in some instances may keep the data from being transmitted at all. Some relevant questions to think about when considering your network and real time data transmission potential include:
- Are the videoconferencing endpoints available compatible with each other (i.e. Polycom to Polycom, Tandberg to Tandberg, Polycom to Tandberg, etc…)?
- Are the videoconferencing sessions going to be point-to-point, multipoint, or bridged calls?
- Are there enough data ports available on the videoconferencing units to connect the equipment?
- Is there a plan in place for firmware updates to get the required unit functionality necessary as required?
- Is your network prone to dropped packets, lending it to degraded sound and/or video quality even before additional devices or processes are introduced?
- Are there know buffering or latency issues in your network?
- Do you have enough electronic stethoscopes or budget to purchase enough hardware to place at both the sending and receiving ends of a network, which are necessary for the required serial data conversions?
- Do you have the budget for the software required to do device to device direct network connections over desktop, along with the accompanying secure desktop videoconferencing software?
- When utilizing the VTC units as a codec, is the sound playback of acceptable quality?