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Popular Articles (October 2014)

Includes the top 50 most frequently downloaded documents for this publication according to the most recent monthly usage statistics.
  • 1. Push-pull class-AB transformerless power amplifiers

    Page(s): 6 - 14
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (562 KB)  

    One of the major problems in power-amplifier design is to combine high efficiency with thermal stability. Class-C operation with current drive is one possibility but distortion level is high due to crossover and nonlinearity of hFE. A new diode-compensation method is described which allows high efficiency Class-AB operation for maximum output and lowest distortion and with excellent thermal stability. In the output stage the variation of the quiescent current vs temperature is kept small by a diode-resistance network in the emitter of each driver transistor, thereby eliminating the need for large thermal compensating resistance in the emitters of the output transistors. A 10-watt amplifier was designed using the described power-dissipation criteria and the new biasing scheme. Performance of the amplifier demonstrates the effectiveness of the design. It operates with maximum power dissipation up to 65°C ambient with a sine wave input. Calculations are also included in the paper which show the voltage levels of maximum power dissipation for sine, triangular and square waves. View full abstract»

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  • 2. Active low-pass filter design

    Page(s): 104 - 111
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (675 KB)  

    The characteristics of Bessel, Butterworth, and Chebyshev filters are briefly reviewed. The "Rauch" RC active low-pass filter configuration is described and design formulae are obtained. Tables of normalized capacitor values are provided for Bessel, Butterworth, and ±½ dB, ±1 dB, ±2 dB, and ±3 dB Chebyshev filters. Two examples indicate the use of the tables. View full abstract»

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  • 3. Tracking distortion as phase modulation

    Page(s): 41 - 46
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    In support of the urgency for establishing a standard for the vertical tracking angle in stereo disc recording, the phase perturbing character of tracking error distortion is shown, and used to calculate the phase and amplitude intermodulation distortion (PIM and AIM) and harmonic distortion arising from tracking errors. These results are compared with those of other authors. Phase cross modulation (PXM) between the stereo channels is demonstrated and offered as the basis for measurement of tracking errors. Psychoacoustic consequences are considered. View full abstract»

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  • 4. Voltage controlled attenuators using field effect transistors

    Page(s): 112 - 120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (893 KB)  

    A FET operated so that channel pinch-off is avoided behaves like a voltage controlled variable resistor. This paper considers a "voltage divider" attenuator using the device in this way. Attenuation (in decibels) varies almost linearly with control voltage over a range. Distortion may be less than 0.01 percent, temperature effects are usually negligible, and the network can operate satisfactorily up to a few megahertz. Circuits of this kind demand a FET having special characteristics. View full abstract»

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  • 5. A rational approach to sound system planning

    Page(s): 96 - 98
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (350 KB)  

    The importance of basic planning for sound amplification and reinforcement systems is discussed. The first step in basic planning is to determine the functions of the sound system by a study of the building and use requirements for the system. A list of objectives or "functional requirements" will serve as the basis for sound system planning and can be interpreted by signal flow diagrams. These can then serve as the basis for the more detailed functional diagrams or wiring diagrams of the sound system. After determining the functional requirements of the system, the designer proceeds with the acoustical and architectural planning. A basic decision is the choice of either a central or a distributed loudspeaker system. This is followed by a determination of the location and orientation of microphones and loudspeakers and the selection of the actual transducers required for the job. Finally, control and amplification equipment are selected. Basic planning is presented as a portion of the overall effort that includes the detailed electronic design of the system, a specification if one is required, careful installation, and final adjustments. View full abstract»

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  • 6. A study of the field around magnetic heads of finite length

    Page(s): 21 - 27
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (406 KB)  

    This paper gives a determination of the field around magnetic heads of finite lengths and infinite permeability. The conventional Schwartz-Christoffel [3] transformation was used to map the inside of the polygon, corresponding to a finite magnetic head, into the upper half of the w plane. The mapping equation was derived and the equipotential lines, corresponding to a particular head-to-gap length ratio, were calculated. The equipotential lines for the same ratio were determined experimentally using the analog field plotter. A comparison of the two sets of curves shows that they are in fair agreement, the discrepancy being due to inaccuracy in the experimental measurements. Finally, the study includes a brief discussion of how the use of magnetic heads of finite lengths would increase the packing density of recorded pulses in both RZ and NRZ types of recording. View full abstract»

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  • 7. Electron microscopy studies of the surfaces of magnetic recording media

    Page(s): 15 - 18
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1311 KB)  

    A technique has been developed for replicating the surfaces of magnetic recording media. The media used included new magnetic tape, used magnetic tape, and "Hypalon" disks; this latter material is used in recording belts. Magnifications ranged from 10,000 × to 80,000 × direct magnification, and up to 240,000 × by photographic enlargement. The electron micrographs thus obtained show a very much smaller unit crystal size for γ-ferric oxide than previously supposed. There is also an apparent relationship between the magnetic properties and the dispersion and unit particle size of the iron oxide particles on the tape surface. View full abstract»

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  • 8. A new approach to a space-confined magnetic loop induction system

    Page(s): 47 - 51
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (550 KB)  

    An investigation of possible communication systems for use in schools for hard-of-hearing children is described. The requirements are set forth and the relative merits of various systems are briefly discussed. A new concept, "The Orthogonal-Fields System," is shown to have definite advantages in those cases where several adjoining rooms have to be addressed independently. In this system the magnetic field, which is the coupling medium between the teacher's microphone amplifier and the pupils' hearing aids, is confined to a limited space. Within this "hearing space" the field strength of the vertical component remains virtually constant, yet it decreases rapidly outside the space. An analytical design for the required loop configuration is given in the companion paper. Measurements on an actual system have shown that the horizontal discrimination is excellent and closely follows theoretical prediction. The loop configurations considered, however, have poor vertical discrimination due to an unfulfilled requirement for vertical asymmetry. Although it is feared that this requirement will be difficult to meet in practice, the system may still be the best available and can be quite useful, especially in new schools where the dimensions of the classroom can be chosen to overcome this limitation. View full abstract»

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  • 9. DC and modulation noise in magnetic tape

    Page(s): 100 - 105
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (841 KB)  

    In a perfect particulate recording medium, noise would not be a function of magnetization. In practice, two types of noise occur which are functions of magnetization-dc noise and modulation noise. Both of these usually have been attributed to either nonuniformity of particle dispersion or imperfections in tape motion. The significance of surface effects has been overlooked in the past. A new experimental technique is described, which makes it possible to determine whether a particular type of noise is fixed or random relative to location along the recording medium. It also enables comparison and identification of noise produced in various ways. It has been possible to isolate and measure the components of dc and modulation noise produced by surface asperities and bulk non uniformity. Apparent anomolies in previously observed spectral and amplitude characteristics of dc and modulation noise has been resolved. View full abstract»

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  • 10. Loudspeaker testing by PAR meter method

    Page(s): 94 - 100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (722 KB)  

    The object of the PAR meter is to provide a single number rating of the fidelity of a transmission system. Loudspeakers are members of this class and hence this meter can be used to evaluate them quantitatively. The rating is a weighted measure of the total gain and of phase distortion in the transmission system. This is a time-domain measuring set. The letters PAR stand for peak to (full wave) average ratio. The PAR meter measures the ratio of the peak to the full wave, rectified average value of a low-duty-cycle pulse signal. The test-signal spectrum used for this measurement can be tailored to produce the desired distortion sensitivities at various frequencies. Some of the results obtained in the use of this instrument in rating loudspeakers are presented here along with a discussion of its potentials. View full abstract»

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  • 11. Charge transfer process in electrostatic recording

    Page(s): 63 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (429 KB)  

    The physical mechanisms responsible for charge transfer between the electrodes and the dielectric tape material of a dc biased electrostatic recording system are discussed. The dominant mechanism for charge transfer is found to be spark discharge in the ambient air. On this basis, a serniquantitative description of the charging process is developed which is in good agreement with the experimental current-voltage characteristics. View full abstract»

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  • 13. On the theories of AC bias used in magnetic tape recording

    Page(s): 78 - 81
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (367 KB)  

    This paper is concerned with experiments that were run for the purpose of supporting or discounting the various alternating current bias theories concerned with direct recording onto magnetic tape. Only the theories of Toomin and Wildfever, and Camras were found to be compatible with the results. View full abstract»

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  • 14. Experiments with electron scanning for magnetic recording and playback of video

    Page(s): 93 - 96
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (703 KB)  

    Present-day video tape uses high-speed mechanical scanning, with rapid wear of tape and heads. Electron-beam scanning is proposed to eliminate mechanical problems and to allow the use of low cost tape. Development work has been conducted on a recording tube using a high-density sheet beam to energize a simplified 500- element magnetic head. For playback a tube was built with a line of fine high-permeability wires sealed into the envelope in the beam path. View full abstract»

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  • 15. A new high-frequency horn

    Page(s): 202 - 206
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (478 KB)  

    A new horn was designed with reduced taper rate and mouth size as compared to an existing horn. Low-frequency response was improved by adding a flange or baffle. Comparison with the existing unflanged horn of similar length shows ability to radiate a wavelength 20 per cent longer. The reduced exit angle provided an unexpected gain in high-frequency range and smoothness of response. With a new wide-range driver, the horn produces smooth response at frequencies more than an octave higher than the old horn and driver. Thus, the bulkier horn with 500-5000 cps response and a tweeter may be replaced with a single horn having 260-17,000 cps response. View full abstract»

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  • 16. Considerations in high-fidelity moving-coil earphone design

    Page(s): 188 - 194
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (727 KB)  

    The theory of simple moving-coil earphone behavior is briefly described. Some considerations concerning the measurement of sound pressure response and harmonic distortion are mentioned, with special reference to difficulties encountered at high frequencies. Several design objectives are presented, followed by a discussion of design techniques including two new approaches: 1) the introduction of a damping grease into the air gap of the magnetic structure for increased power handling ability, smoother sound pressure response and improved transient performance near the fundamental resonance; 2) a resonant back-loading cavity for improved low-frequency performance when air leaks are present. View full abstract»

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  • 17. A versatile tone control circuit and preamplifier

    Page(s): 195 - 201
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (446 KB)  

    A tone control circuit is described which allows a large choice in the high- and low-frequency attenuation or boost and in the position of the tone compensation curves over all the acoustic spectrum. These two controls, which are completely independent, are obtained with structurally simple RC networks. This tone control is included in a preamplifier for music reproduction. The compensation and equalization curves are reported in the paper and the characteristics of the complete preamplifier are described. View full abstract»

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  • 18. Notes on how phase and delay distortions affect the quality of speech, music and sound effects

    Page(s): 23 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (271 KB)  

    Phase and delay distortions in the reproduction of speech and music have always been an important consideration in the design of high-quality systems. Early authoritative literature indicated this type of distortion could be disregarded. In 1935, events occurred in which phase delay in a two-way loudspeaker severely distorted sound effects. From this observation, a research program was set up to evaluate the minimum detectable delay that could be tolerated in two-way theater type loudspeakers; the final recommendation was 2 ms. During the period of 1930 to 1940 an intensive redesign of recording equipment was made for lower phase shift, and the quality increase is now long a matter of record. View full abstract»

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  • 19. Fundamental accuracy limitations for pilot-tone time-base correction

    Page(s): 53 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB)  

    Wiener filtering concepts are applied to the problem of determining the accuracy limitations for a pilot-tone time-base correction system. Pilot-tone time-base correction is currently employed in speed control of tape recorder drives, vernier data correction by means of voltage-controlled delay lines in wideband tape recorders, as well as synchronized sound-on-film devices. In this system, the correction is accomplished by the addition of a stable sinusoid in a clear area of the signal baseband. After transmission through a medium with varying time delay and additive noise, the pilot tone is recovered by a tracking filter. The output of the tracking filter can be used to estimate the variations in time delay of the transmission medium. A statistical optimization is then performed to find the minimum residual time-base error in the desired signal after correction by such a system. The theory of parameter estimation indicates that the system described is near optimum and represents a lower bound on achievable accuracy. The results for the special case of white bandlimited time-delay variations are presented in the form of curves. View full abstract»

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  • 20. The RC amplifier-type active filter: A design method for optimum stability

    Page(s): 66 - 71
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (455 KB)  

    The RC amplifier filter has many advantages over its passive RLC counterpart for low-audio frequency or narrow-band applications. The major disadvantage to an active filter has been its sensitivity to component tolerance and drift, particularly where high Q's are involved. A design method is presented which optimizes transmission stability when the probable "drift" (tolerances, temperature and aging effects, tracking errors) in each circuit parameter is known. Design equations are derived for a group of two-pole networks with external zeros. Two experimental high-Q filters are discussed including a continuously tunable four-pole filter which has attenuation of 80 db at twice and at one-half center frequency. View full abstract»

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  • 21. Conditions for optimum noise performance of transistor amplifiers with a reactive source

    Page(s): 15 - 22
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (622 KB)  

    When driven from a purely reactive source, conventional noise figure is undefined for a two-port network such as an audio amplifier. In order to assess the noise performance of small-signal amplifiers driven from reactive sources such as capacitor microphones, a signal-to-wideband-average-noise ratio is defined. It is shown that for transducers where output is related to internal reactance by a simple transformer relationship and where the Thevenin equivalent internal impedance is a pure seriesRandLorC, there exists an optimum value of internal reactance for maximum signal-to-noise ratio when used with a given noisy amplifier. The equations for optimum reactance and signal-to-average-noise ratio are general and include low-frequency dependence of the transistor noise generators, equalization or frequency dependence of amplifier gain, and source resistance as well as reactance. Solutions are given for the practical audio case with typical low-noise audio transistors for both inductive and capacitive transducers. View full abstract»

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  • 22. Pitch perturbation detection

    Page(s): 9 - 14
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    Pitch perturbations are defined as normally minute variations in the lengths of adjacent pitch periods of voiced speech. It has been shown that perturbations increase in size and number in the presence of laryngeal abnormalities such as cancerous growths. Previous studies have been limited by the unavailability of electronic equipment of sufficient accuracy to perform the pitch measurements in real time. The apparatus to be described represents an intermediate step in the design of a real-time perturbation detector. Operating in an expanded time scale and using regenerated pulse trains derived from visual measurement of voiced waveforms, perturbation measurements are made which are comparable with the computer-calculated values. View full abstract»

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  • 23. The specification of loudspeaker characteristics

    Page(s): 115 - 117
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB)  

    In specifying loudspeakers for use in a sound system, the designer can simply list acceptable manufacturers' type numbers, or he can attempt to write appropriate performance specifications. Either approach is made difficult by the general unavailability of adequate information on characteristics of commercial loudspeakers. The most important characteristics are discussed, with emphasis on directional properties and methods of measuring them. View full abstract»

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  • 24. A "Microlithic" hearing aid amplifier

    Page(s): 118 - 120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (618 KB)  

    This paper covers the development of an integrated solid-state amplifier from initial considerations for using such a device up to the completion of the first integrated amplifier. View full abstract»

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  • 25. Analytical design of magnetic loop induction systems

    Page(s): 51 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (933 KB)  

    The method of orthogonal fields, presented in the companion article, permits the design of a loop system with little spreading out of the resultant magnetic field. This article describes the mathematical basis of the design. Good approximation and ease of handling are obtained by the use of complex function theory and conformal mapping. Two solutions for the problem emerge, one based on the properties of hyperbolic functions, the other on those of elliptic functions. In the first solution, the field decays monotonically to zero outside the primary area of communication. In the second solution, the field exhibits equiripple character in the region where communication is to be prevented. The ultimate design was chosen from the second category, after elaborate computation with the help of an electronic computer. View full abstract»

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  • 26. A study of tracking-angle errors in stereodisk recording

    Page(s): 56 - 62
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (810 KB)  

    Lateral tracking-angle errors are easily controlled in stereodisk systems and present no serious problems. Vertical tracking-angle errors are much less easily controlled and frequently are the cause of serious harmonic and intermodulation distortion in playback. The mechanisms producing vertical tracking-angle distortion are outlined. Among other things, it is shown that IM products due to frequency-modulation effects in a multicomponent signal are particularly serious. It is shown, also, that the effective tilt angle in a recorder, while cutting a groove, may be considerably different from the nominal tilt angle determined by the internal geometrical configuration of the cutter. This difference can be attributed to bending of the recording stylus as a result of the drag force of the record material being removed from the groove. With present understanding it should be possible to reduce the distortion due to vertical tracking-angle errors to negligibly-low values in stereodisk systems. View full abstract»

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  • 27. Loudspeaker testing in reverberant rooms

    Page(s): 34 - 40
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (849 KB)  

    In the diffuse sound field of a reverberant room acoustical intensity is directly proportional to the acoustical power emitted by a source and inversely proportional to absorption in the room. If the room and microphone characteristics are known, pressure response curves of loudspeakers can be plotted which are proportional to the total acoustical power radiated by the loudspeakers. The instrumentation procedures used in mean energy density (MED) testing are described in detail with particular emphasis on the facility at the Jensen Manufacturing Company, and the role of MED measurements in the evaluation of loudspeakers is discussed. View full abstract»

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  • 28. Voice recording in space

    Page(s): 141 - 145
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    Manned space flight uses one of the oldest communications media, speech, and a voice recorder is required to store it. CBS Laboratories developed the voice-time recorders for the NASA Gemini missions, and flights have proved their effectiveness. The small, light, reliable device records the mixed voices of the astronauts on one track and a digital time signal on the other. Cartridges with one hour capacity can be changed during orbiting, which permits taking as many cartridges as the mission duration requires. Tape is 0.110 inch wide, moves at 0.6 in/s and is contained in a unique coaxial-reel bidirectional cartridge. An ac synchronous motor, energized from a dc to ac converter, drives the mechanism at constant speed. Ground players/duplicators allow convenient transcription and time correlation of the cartridges. View full abstract»

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  • 29. The vertical tracking angle problem in stereophonic record reproduction

    Page(s): 47 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1311 KB)  

    At the time of the widespread introduction of stereophonic records in 1957, two cutter systems became available-one embodying a 23° vertical recording angle and the other a 0° angle. In 1961 the Engineering Committee of the RIAA recommended a 15° vertical tracking angle standard for stereophonic pickups. In the intervening years, however, the matter of vertical angles appears to have been neglected by most pickup makers in as much as a range of angles of 0° to over 40° has been reported, in the extreme cases audible distortion being noticed. A new factor has been added by recent CBS Laboratories' discovery that, because of lacquer and stylus springback, the actual slant of the recorded wave is considerably smaller than the recording angle. With 23° cutter normally used, for example, the actual modulation angle is near 0°. A special mounting and special recording stylus have been developed for providing the cutter with an added inclination of 14° which produces the desired 15° effective modulation slant. Modulation slants can be measured by microscopic measurements of dissymmetry of square-wave traces, by measurements of the shift of optical patterns, by measurement of distortion with the forward and reverse pickup orientation on a test record, and by placing the pickup in a normal and an inclined playing position. This latter method of measurement also yields the effective value of pickup tracking angle including the effect of any existing longitudinal elasticity of the stylus mounting. View full abstract»

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Aims & Scope

This Transactions ceased production in 1965. The current retitled publication is IEEE Transactions on Signal Processing.

Full Aims & Scope