Sound Fidelity Research Articles

High-Intensity Interval Training-Based Fitness Education in Middle School Physical Education: A Limited-Efficacy Study

Purpose: The purpose of this study was to evaluate the limited efficacy of a high-intensity interval training (HIIT)-based fitness education unit in middle school physical education (PE). Method: The study took place in six PE classes at one middle school located in the southern United States. The authors conveniently assigned the classes to treatment (n = 3 classes; 113 students) or control (n = 3 classes; 119 students) groups. Two trained PE specialists implemented the HIIT lessons two to three times per week for 8 weeks. The authors collected mixed methods data at the student, class, and teacher levels for the evaluation. Results: The focus group teacher interview with the teachers, field observations, and accelerometer-determined in-class physical activity data revealed sound implementation fidelity. The HIIT-based fitness education condition also showed greater improvement in physical activity and fitness knowledge and attenuated decline in curl-up scores compared with the control. Conclusion: The findings support the limited efficacy of implementing HIIT for fitness education in middle school PE programs.

Rethinking criticism about lossy compression: Sound fidelity, large-scale production and audio capital in pop music

Although digital music streaming and downloading practices highlight a preference for portability over fidelity among pop music consumers, for some ‘high fidelity’ continues to be a crucial component of their pop music engagement. This article examines the political dimensions of audio preferences. It considers comments by Neil Young and those within The Distortion of Sound who claim that the lossy compression encoding process – used in digital downloading and streaming – significantly degrades the quality of recorded sound and compromises valuable pop music characteristics. In 2015, these claims were followed by the development of the ‘hi-res’ music player device and digital download store ‘Pono’. This article argues that some criticism of lossy compression can be understood as ‘audio capital’. Rather than merely exchanging aesthetic preferences, or a reliable metric of the audibility of high fidelity, audio capital describes the reconversion of celebrity status and economic capital into a class divide structured by an appreciation for large-scale music production.

Comparing Light-Driven Contact Hearing Aids with Acoustic Hearing Aids: Data and Clinical Tips

Introduction: Contact hearing aids (CHA) offer potential advantages over conventional acoustic hearing aids (AHA) in terms of sound quality, reduced occlusion, and increased high-frequency gain. This study evaluates objective and subjective outcome data for CHA compared to AHA. Methods: Clinical outcome data were retrospectively reviewed for patients wearing CHA. Individual and group data were analyzed and then compared to unaided and AHA data. Adverse effects, device complaints, and clinical utility were documented throughout the device fitting and follow-up process. Results: CHA outcomes were better than unaided hearing and AHA for all patients completing the 3-month CHA trial period (45%). However, CHA return rate was high (55%), most often due to device repair and fit issues. Two patients returned the devices due to poor hearing benefit, though both were off-label audiometric candidates. Significantly more clinical time was required from both audiologists and otolaryngologists to successfully fit and maintain maximum device benefit. Conclusions: For proper audiometric and otologic candidates, this light-driven CHA can offer significant improvements in high-frequency sound fidelity, word recognition, and sound quality compared to AHA technology. Administering questionnaires was helpful in illuminating real-world improvements. Device fit, alignment, and quality control issues are improving, though still contributing to high device return rates at this time. Operational factors should be considered when incorporating CHA into a hearing health care practice.

Deer browsing alters sound propagation in temperate deciduous forests.

The efficacy of animal signals is strongly influenced by the structure of the habitat in which they are propagating. In recent years, the habitat structure of temperate forests has been increasingly subject to modifications from foraging by white-tailed deer (Odocoileus virginianus). Increasing deer numbers and the accompanying browsing have been shown to alter vegetation structure and thus the foraging, roosting, and breeding habitats of many species. However, despite a large body of literature on the effects of vegetation structure on sound propagation, we do not yet know what impact deer browsing may have on acoustic communication. Here we used playback experiments to determine whether sound fidelity and amplitude of white noise, pure tones, and trills differed between deer-browsed and deer-excluded plots. We found that sound fidelity, but not amplitude, differed between habitats, with deer-browsed habitats having greater sound fidelity than deer-excluded habitats. Difference in sound propagation characteristics between the two habitats could alter the efficacy of acoustic communication through plasticity, cultural evolution or local adaptation, in turn influencing vocally-mediated behaviors (e.g. agonistic, parent-offspring, mate selection). Reduced signal degradation suggests vocalizations may retain more information, improving the transfer of information to both intended and unintended receivers. Overall, our results suggest that deer browsing impacts sound propagation in temperate deciduous forest, although much work remains to be done on the potential impacts on communication.

Wax Power

Wax Power Jeffrey R. Di Leo (bio) The advent of vinyl records was paved by a fifty-year journey that began with a stylus reading a groove on a wax cylinder. Thomas Edison's phonograph, which converts the wax cylinder's grooves into sound via a diaphragm, was developed in 1877. The first sound recording played back on the phonograph was Edison mouthing the words, "Mary had a little lamb." The first commercially available vinyl long-playing records were produced by RCA in 1931. But prior to 1958, there were no commercially available sound recordings in stereo. That would all change though when the record company, Audio Fidelity, previewed a "stereo" long-playing recording at the Times Auditorium in New York City on December 13, 1957. On one side of the LP was a stereo recording of the Dukes of Dixieland jazz band, and on the other, were railroad sound effects from steam and diesel locomotives. The initial print run was 500 records, and Audio Fidelity offered free copies through an advertisement in Billboard magazine to anyone in the music industry that asked for one. Then, on December 13, 1957, they introduced the first-ever commercial recordings in stereophonic two-channel sound—and by the end of 1958, stereo LPs would be commercially available by every major record label. In one sense, the story of sound recording begins with Edison's words, and moves through nearly one-hundred and fifty years of sound recording development from wax cylinders and vinyl records to compact discs and MP3s. The standard tale here is one of increasing levels of sound fidelity with events like the staging of stereophonic sound with railroad sound effects marking significant progress in sound fidelity. It is the story of a journey from the low fidelity of the gramophone to the high fidelity of the compact disc. However, in another, more philosophical sense, the invention and development of the phonograph marks a very late stage in the development of sound recording—a journey that dates back to a power first attributed only to the gods. What brings together both the story of the early stages of sound recording and the story of its later stages is the general idea that power comes through the ability to control sound in society. My term for this form of power is "wax power." _______ The ancient gods were said to have three essential powers: making war, causing famine, and recording sound. This might seem like an odd triumvirate of powers, particularly the latter power, but imagine a world where there is no means to store information other than memory. The sounds that we make to each other in discourse, and those that we hear in the world around us, can only be repeated and passed along to others through acts of memory. It is somewhat fitting then that when the ancient Greek philosopher, Plato, discussed memory in his philosophical dialogue Theaetetus, he asked us to imagine it in one sense as a "block of wax, which in this or that individual may be larger or smaller, and composed of wax that is comparatively pure or muddy, and harder in some, softer in others, and sometimes just the right consistency." "Let us call it," says Plato, the gift of the Muses' mother, Memory, and say that whenever we wish to remember something we see or hear or conceive in our own minds, we hold this wax under the perceptions or ideas and imprint on it as we might stamp the impression of a seal ring. Whatever is so imprinted we remember and know so long as the image remains; whatever is rubbed out or has not succeeded in leaving an impression we have forgotten and do not know. Though the imprinting of perceptions or ideas on wax here has more in common with block printing than a stylus making sound impressions on soft wax, the notion that this act might be regarded as "the gift" of a god to humankind assumes that the actual power of total memory is one held by the gods—and not humankind. Plato also says that Homer too struggles to explain human memory, and "hints at the mind...

Media as an Invitation to Rethink Music Education

This column explores from a philosophical perspective how sound recording and media create a context different in consequential ways for music education. The author relates the story of his connection to his son through the ukulele in two ways: first, through playing and singing together; and second, through a recording of their music. These differences are explored through a pragmatic approach to technology, with a focus on three issues: commoditization, efficiency, and sound fidelity. The author then explores two different kinds of responses that educators might explore in thinking about music education contexts and media awareness: an approach to focal practices following Borgmann, and the technological transparency approach recommended by Dewey.

A Molecular Voltmeter Based on Fluorescence Dynamics

In this issue, Hou et al. (1) introduce an elegant method for measuring the absolute voltage across a cell membrane with an accuracy of 10 mV. Their study presents an incisive approach to voltage imaging in which the voltage value is encoded in the temporal dynamics of fluorescence rather than in the raw fluorescence intensity. Together with an engineered microbial rhodopsin with properties amenable to the approach, the method provides a genetically encoded optical read-out independent of the reporter’s expression level and insensitive to variations in common experimental parameters. Their work presents a conceptually new avenue toward developing probes for membrane voltage useful for myriad systems from bacteria to mammalian tissue.

The California schedule of key ingredients for contact-based antistigma programs.

A major public health priority has been to eliminate stigma's egregious effects on life opportunities for people with mental illnesses. Research shows contact-based antistigma programs are among the most effective. Such findings call for clarity to define the components of consumer-directed antistigma programs. This article represents community-based participatory research (CBPR) and the first step of a mixed methods design to describe the active ingredients comprising these kinds of programs. CBPR investigators developed an interview guide and subsequently facilitated four focus groups to identify key components. Participants included antistigma experts with lived experience. Using grounded theory, two independent raters identified 641 discrete themes. Two additional coders then sorted themes into constructs representing key ingredients of contact-based programs. Coders agreed upon 198 constructs and then grouped them into a hierarchical model of key ingredients in consumer-directed stigma change. Five criteria represent indicators of successful consumer-directed programs: (a) program design-factors necessary for trained presenters to facilitate programs; (b) targeting-tailored presentation congruent with target's goal; (c) staffing-facilitators and leadership are diverse people with lived experience; (d) messaging-presentation discusses struggles and recovery from mental health challenges; and (e) follow-up and evaluation-assessment of sustained audience change. This study identified key ingredients of consumer-directed antistigma programs. Part two of the mixed methods design, a quantitative cross-validation study, will yield a sound fidelity measure.

HEARING DEVICE WITH SEMIPERMANENT CANAL RECEIVER MODULE

A modular canal hearing device having a speaker module placed in the bony region for extended wear while a main module is removably inserted in the cartilaginous region. The main module wirelessly activates the speaker module when placed in proximity thereto. The main module is removed daily or as needed for maintenance of the hearing device such as for battery replacement. The speaker module remains undisturbed in the bony region to avoid skin friction. The main module contains the microphone, electronics, battery and in the preferred embodiment an inductive coupling coil for inductively sending audio signals to the receiver module. The modular design allows for a highly miniaturized design that is easier to navigate in the ear canal for improved fit and sound fidelity at the eardrum while allowing easy maintenance of a removable module.

A new sinusoidal model for synthesis of musical instruments

Many algorithms have been developed over the years to synthesize acoustic sounds and are now used commercially in acoustic synthesizers and digital keyboard products. The issue with these algorithms is the tradeoff among sound fidelity, algorithm complexity, and hardware/storage requirements-the last two of which are directly related to the cost of the system. In this reported work, we introduce a new sinusoidal model for digitally synthesizing musical instruments. The new algorithm has unusually high fidelity, minimal memory requirements, and high computational efficiency. The algorithm is based on the “analysis-by-synthesis overlap add” (ABS/OLA) sinusoidal model, which models musical sounds as a short-time weighted sum of constant frequencies, phases, and amplitudes. The new model we introduce incorporates a novel dynamic pitch and frequency control feature in synthesis that allows very high quality instrument sounds to be generated over a wide range of pitches from a very short sampled recording of the musical instrument. Sound modifications can be performed parametrically within the framework all using fast Fourier transforms (FFTs) for high efficiency. Examples of synthetically generated non-western musical instruments will be presented during the conference and contrasted with competing technologies to illustrate the advantages of the new method.

A Sound that Never Sounded

/ Cylinder recordings as an early form of reproducible sound media were first used in 1877 and continued to be produced commercially up until 1929 by Edison. The many cylinders that exist today in various states of decomposition have become objects of concern for those with an interest in historical sound recordings. With this concern leading to preservation efforts converting cylinder sounds into digital form, how should a cylinder sound and with the transformative potential for digital manipulation readily available, how should a digital file of a cylinder record sound? This article discusses the production process of both cylinder recordings and their digital conversions, revealing how fidelity never actually existed in the production process. The University of California Santa Barbara's Cylinder Preservation and Digitization Project exemplifies a digital preservation project that reveals what is valued during the digital conversion process. By describing how the cylinders are imbued with meaning through the concerns of manufactures, archivists, internet users and collectors, this article proves that processes concerned with the objectification of sound are motivated by specific social and technological desires motivated by nostalgia for an imagined sound fidelity.

Head set speaker and stereo playing device

A head set speaker and stereo radio playing device exhibits improved harmonics and acoustic fidelity. A resilient and flexible headpiece is sized to fit behind the head of the user. Right and left device enclosures are carried by the ends of the headpiece, and are aerodynamic shaped to minimize wind whistle which may result when the head set is worn while moving rapidly. Right and left behind the ear flanges extend downwardly from a position adjacent to the ends of the headpiece, and aid in the positioning of the right and left ear device enclosures. In a typical application, the device enclosures are positioned immediately forward of the user's ears, allowing ambient sound to be heard. A speaker assembly and a removable battery assembly are carried within each device enclosure. The speakers are oriented within the device enclosures with the speaker magnet directed to, and in contact with, the head of the listener. This achieves two interrelated and significant structural and electronic advantages. First, sound fidelity is improved by using sound reflecting walls and baffles to redirect the sound. And second, antenna functionality is improved by attaching an antenna input to the speaker magnet which is in contact with the listener's skin, and there by connecting the listener's body to the antenna. A charging unit is sized to receive both battery assemblies simultaneously. A circuit card carried within one of the device enclosures contains a stereo radio circuit. On/off, volume up, volume down, scan and reset buttons carried by the device enclosures are in electrical communication with the circuit card, and allow control over radio functionality.

Efficient method for harmonics estimation of car engine sounds: application to high quality real‐time synthesis

Additive synthesis is the most popular method for the resynthesis of sounds containing slowly evolving harmonics or partials, such as car engine noise and more generally rotating machines sounds. The most important step lies in the estimation of the amplitude and frequency of each sinusoidal component. It appears that insufficiently precise estimation often leads to unsatisfactory results in terms of sound fidelity. A method providing the time and frequency evolution of the amplitude of the harmonics of a recorded sound is presented. This technique is based on a joint time and frequency chaining of amplitude's extrema of amplitudes coming from a short‐time Fourier transform, using forward and backward estimation. The proposed method is compared to a rough estimation, and to an estimation based on measured tachometric data, all carried out over the same car engine sound. This estimation method is implemented into the LEA software, which thus allows fast and precise computations of the parameters. Moreover,...

Application of piezoelectric multi-layered actuator to floating mass transducer for implantable middle ear hearing devices

Implantable middle ear hearing devices (IMEHDs), which have been developed since the 1970s, directly stimulate the middle ear and can realize a high efficiency of sound transmission with better sound fidelity. For such kinds of IMEHDs, this paper presents the design and application of a piezoelectric floating mass transducer (PFMT) using a PMN-PT multi-layered actuator as a new type of vibrating transducer. The proposed PFMT consists of only three components of a multi-layered piezoelectric actuator, a metal case, and a clamping clip. The actuator’s one side is connected with the metal case and the other side is linked to the clamp for the attachment to an incus long process of middle ear ossicles. The vibration displacement of the PFMT attached to the incus is studied theoretically by simplified kinetic model between the PFMT and the incus. Through an in-vitro experiment using a human temporal bone, it has been verified that the proposed PFMT can generate the vibration force equivalent to the sound pressure of about 100 dB SPL. Therefore, the proposed PFMT is expected to be used as an IMEHD transducer with the advantages such as simple surgical implantation, no interference from external electromagnetic fields, and improved productivity.

Method and apparatus for spatially enhancing the stereo image in sound reproduction and reinforcement systems

Sound reproduction and reinforcement systems and methods are presented herein for spatially enhancing stereo images typically used such performances as those involving music. The embodiments seek to expand the amount of audience area that would receive a sound image that maintains sound reproduction fidelity regarding spatial orientation of sound sources involved in an original performance. To expand the audience area receiving spatially faithful sound reproduction certain characteristics of sound have been first studied to find important factors involved.

Bioacoustic monitoring of forest songbirds: interpreter variability and effects of configuration and digital processing methods in the laboratory

Omnidirectional bioacoustic recording systems offer the ability to record forest songbirds in the field by technical staff, and then interpret the recordings later in the laboratory by skilled interpreters. Among several advantages to this approach are the ability to estimate variance among interpreters, obtain a permanent archival record of the point count, reduce costs by using regular field crews to collect data vs. those skilled in bird identification, and remove impediments to breeding bird surveys due to lack of available skilled birders. In this study we first evaluated the effects of microphone configuration and digital processing methods on the quality and effectiveness of the recordings, and then evaluated how consistently skilled birders interpreted the same songbird recordings collected under a mix of environmental conditions, and related this to the commonness of the species. At the time of this evaluation, the most cost-effective configuration of the bioacoustic monitoring system included use of a 180°/180° microphone combination, a minidisc digital recording system, analog transfer of the sound data via a digital soundcard, post-processing amplification of the signal, and data storage in an .MP3 format. This combination maintains high sound fidelity while minimizing both expense and data storage requirements. As recording device technology improves, the direct storage and digital transfer of .WAV format files will be the preferred and most effective recording option. Despite noisy conditions due to wind and other ambient sounds for many of the recordings, interpreters showed a high level of similarity in species identification and enumeration for the 34 most abundant species. Standardized coefficient of variance increased sharply when species had fewer than 10 occurrences, suggesting that birders are more variable in their identification of rare or uncommon species. Desktop identification systems that include type specimens of spectrographic signature and sound clips to aid interpreters could improve identification accuracy of rarer species.

Methods to increase sound fidelity and quality produced from piezoelectric devices

Methods to increase sound level, fidelity and quality produced from vibrating lamina such as piezoelectric actuators, vibrating plates or vibrating films are presented. Results of using the methods are shown for piezoelectric devices. Four methods are described: (1) tailoring the vibration response to develop desired deformation shapes and amplitudes, (2) mapping vibration out-of-plane deformation to ascertain locations on the surfaces of lamina suitable for stroke-like actuation, (3) coupling vibration to a collection of acoustic chambers and (4) increasing the vibration decay rate. The first two methods provide a single piezoelectric device with the functionality of numerous actuators combined. A piezoelectric actuator with numerous high-amplitude natural vibration responses has been produced using the aforementioned methods. Numerous high-amplitude vibrations increase the functionality of the devices. A collection of acoustic chambers were affixed to the piezoelectric actuator's surface. The addition of the chambers resulted in more efficient audio output. The result of using all of the aforementioned methods is a high fidelity, high-bandwidth, and high sound-quality audio device with a low physical profile. The use of the piezoelectric actuator effectively results in an audio driver with a thickness less than 1 mm. The piezoelectric audio device achieved a response of 93±4 dB measured at 1 cm in the frequency range (1–5 kHz) with very good audio output for frequencies less than 1 kHz. The methods can be used to design other devices using solid-state piezoelectric actuators or vibrating lamina (e.g., plates or films).

Acoustical considerations in developing the educational exhibition Mostly Music

Mostly Music is a new exhibition designed and developed by the Pacific Science Center. It will visit nine museums around North America during its 3-year tour. Developing an exhibition on the science and technology of music and musical instruments required consideration of varying background sound levels depending on the number of visitors in the exhibition, cross-talk between exhibits, requirements of sound fidelity and sound isolation, and sound reinforcement in some instances. Design case study will be presented along with anecdotal comments on planned versus actual results on individual exhibits.

Active electronic cochlear implants for middle and inner ear hearing loss--a new era in ear surgery. I: Basic principles and recommendations on nomenclature

Hearing aids have fundamental disadvantages: (1) stigmatization of the patient; (2) the sound is often found to be unsatisfactory due to the limited frequency range and undesired distortion; (3) in many patients, the ear canal fitting device generally necessary leads to an occlusion effect; (4) acoustic feedback when amplification is high. Conventional hearing aids transmit sound into the ear canal via a small microphone. Sound has the disadvantage of requiring high output sound pressure levels for its transmission. This along with the necessary miniaturization of the loudspeaker as well as the resonances and reflections in the closed ear canal contribute to the disadvantages mentioned. In contrast, implantable hearing aids do not make sound signals but micromechanical vibrations. An implantable hearing aid has an electromechanical transducer instead of the loudspeaker of a conventional hearing aid. The hearing signal does not leave the transducer as sound but as a mechanical vibration which is directly coupled to the auditory system bypassing the air. This implantable hearing aid is either coupled to the tympanic membrane, the ossicular chain, the perilymph of the inner ear, or the skull. An implantable hearing aid is expected to have: 1 Better sound fidelity than a hearing aid 2 No ear canal fitting device, free ear canal 3 No feedback 4 Invisibility Requirements on electronic hearing implants designed for patients with conductive hearing loss differ from those on implants for sensorineural hearing loss. Conductive hearing loss requires the implant to replace the impedance transformation, thus being an impedance transformation implant (ITI). In various respects, the demands on an ITI are lower than the demands on an electronic hearing aid for patients with sensorineural hearing loss. The latter are mostly patients with a failure of the cochlea amplifier (CA). A damage to the CA is clinically discernible by a positive recruitment and loss of otoacoustic emissions (OAE). Since these patients form the majority of cases with sensorineural hearing loss, an active hearing implant for such patients should partially replace the function of the CA. Therefore, the suggestion is to refer to a CAI (cochlea amplifier implant). The implant expressions ITI (for patients with conductive hearing loss) and CAI (for patients with sensorineural hearing loss) used in this context allow nomenclatural association with the CI (cochlear implant) for complete inner ear failure as well as with the BSI (brainstem implant) in the case of hearing nerve failure.

Sound Bits and Bytes: An Introduction to Microphones

Sound Bits and Bytes: An Introduction to Microphones John L. Butler C. A. S. Figures Click for larger view View full resolution Figure 2. John Butler: “There are no short cuts. You must learn by doing.” Photo by Victor Maysayesva, Jr. As digital audio becomes the established technology for the field, analogue technologies will continue to recede. And even as more recording processes are applicable in both analogue and digital domains, one process remains the same no matter what—“Hind sight is 20/20...future vision is damn near always blind.” Let’s face economic reality: development of new technologies will last as long as SONY and Phillips, for example, are satisfied with their profits; when the market no longer sustains profit ability, it won’t be possible for manufacturers to continue with their same now-old technology, so they’ll introduce a new technology and a new format. In any case, the task of field recording is rapidly changing. I trust that traditional recording standards will not be replaced by cheap machinery and lower standards, such as we see when traditional studio techniques have been replaced by cheap tape recorders, drum machines, and samplers. I like to look at these new machines as missing links or tools to help the recordist to do his or her job well. New technologies of digital audiotape (DAT), the four-track [End Page 37] Nagra-D, Fostex PD2, the 8 track ADAT, and wireless microphones are changing the way production sound and field recordings are produced. The portable analogue reel-to-reel recorders and Nagra machines still remain the field recordists’ basic equipment, but new technologies offer new options for better field recordings. In time, perhaps, new technology may render the standard field recording package nearly obsolete. The old, standard recording package consisted of analogue equipment: a recorder, a mixer, and microphones. The contemporary sound recording field equipment package may use a combination of the best of analogue and digital technologies. Every production is different, and the choice of format may depend on a variety of factors. Given the wide-range of sophistication in available equipment, I could not suggest a specific format without discussing it with the complete production staff—the producer, the director, the director of photography, editors, post production sound mixers, and the lab. We who work in film sound know that we are always eight to ten years behind what [End Page 38] everyone else is doing in the recording world. Most of the studios have a large amount of money invested in traditional technology and are reluctant to change: why change from tried and true recording methods? New sound technology has offered additional freedom to the sound recordist, allowing him or her to be more adventurous and creative in their work. In the past couple years, consumer technology has, in some cases, out-paced professional equipment; this has muddied the field, so to speak, so that the question of whether a format is “consumer” or “professional has no clear answer. I could go on and on about digital versus analogue. While this debate holds interest for some technology buffs, for the sound recorder there are basics that must be mastered, regardless of technological format, that are necessary for getting the best recording for your project. Microphones The microphone is a transducer that converts acoustic energy to electrical energy. This electrical energy, in turn, is amplified and sent to loudspeakers or headphones. Loudspeakers and headphones are another sort of transducer, and their role is to convert this electrical energy back to acoustic energy—back to a sound that we can hear. For accurate sound fidelity, the sound event picked up by the microphone transducer should emerge from the loudspeaker or headphone transducer without any significant change, unless it is an intended change. Click for larger view View full resolution Figure 3. Diagram showing the field of sound sensitivity in a cardioid microphone. Microphones are classified by their patterns. A microphone pattern refers to the shape of the particular area surrounding a microphone, from which the microphone is capable of picking up sound. Thus, we can identify microphones by their directional properties. There are four basic types of microphones: the...