Sound Recording Handbook by John M. Woram. Howard W. Sams & Co., Indianapolis, 616 pp., hardcover, $49.95.
John Woram is well known in the professional audio field. He was editor of dB magazine for many years, and his earlier book, The Recording Studio Handbook, was a standard text in audio-recording education. This, his new book, is part of Howard W. Sams & Company's John Woram Audio Series.
Because Woram is a journalist and recording engineer with many credentials, one expects that he will bring a high level of competence and clarity to the presentation of technical ideas. His writing is always direct, and the chain of cause and effect is never broken. While his earlier book spent more time in the studio, this new book goes into far greater depth. It is truly a hand book, in terms of its vast reference capabilities, but it is also a fine text for teaching.
The book opens with basic audio theory. Here are covered the elements of logarithms, the decibel, trigonometric functions, and basic waveform analysis. Acoustics is covered in terms of sound intensity and power, the wavelength-dependent nature of sound reflection, refraction and diffraction, and, finally, a discussion of sound fields.
In a chapter called "Music, Electronics, and Psychoacoustics," Woram discusses the importance of musical knowledge on the part of the recording engineer. Such topics as the harmonic series, evolution of musical scales, and harmonic analysis are presented, along with loudness and localization.
Woram's chapter on microphones is extremely detailed, both in terms of operating principles and pattern derivation. Woram further elucidates microphone pattern control in terms of such concepts as random energy response, random energy efficiency, directivity factor, distance factor, unidirectional index, and front-to-total ratio. While not all of these terms are standard, or even necessary to define a given pattern, they all assist the reader in gaining an intuitive feel for what microphone directivity is all about--i.e., the relationship between the useful acceptance angle of the microphone and its overall response to diffuse, random acoustical power. Stated in other terms, we use a cardioid microphone not because it is supposed to reject sounds originating at 180° but because it has the desired acceptance angle and is some 5 dB less sensitive to random sounds than to sound sources located along the principal axis. This is the essential rationale for directional microphones, and it is often misunderstood by neophyte engineers. The author's lengthy exposition goes far in clarifying the matter. With the microphone fundamentals covered, Woram then moves on to a discussion of the first-order cardioid family, presenting directional data both in the familiar polar form and in the Cartesian coordinate form normally favored by radar and sonar engineers. Such matters as proximity effect and off-axis coloration are then covered.
Stereo microphone theory is then presented, first as coincident technology as seen in X-Y/M-S equivalence and then as quasi-coincident and spaced techniques. Woram's cover age of M-S is surely the most detailed in current literature, and there are many equations to daunt the neophyte. However, the text is still clear enough, in an intuitive sense, for the student to get the gist of it all. As stated earlier, the value of this work as a handbook is underscored by such depth of detail.
The author then moves on to methods of synthesizing various patterns by combining the patterns of two micro phones. This ultimately leads to a discussion of the Soundfield microphone, in which four directional elements can be combined to produce first-order cardioid-family patterns oriented to ward any direction around, above, and below that microphone. The problems solved by the use of boundary layer microphones are then detailed.
The following chapter is on monitor loudspeakers and is far ranging, covering some loudspeaker types rarely encountered in monitoring (electrostatic speakers, for example). The basic mechanisms are treated, along with bandwidth, directional properties, and the effects of room boundaries. Low- frequency enclosure types are discussed, as are horns and their associated compression drivers. (In general, horns and horn types are covered in more detail than necessary for a book devoted to recording.) Systems concepts come next, with a discussion of dividing networks, time-offset correction, phase shift, and absolute polarity.
Woram then turns to the major areas of signal processing. Delay and reverberation systems are presented first. As a preliminary discussion, the author describes the nature of sound propagation in real spaces in terms of the direct, early, and reverberant fields which are set up. The "real thing" is described before the model is envisioned to duplicate it. Woram then moves on to the problems of recording the various time-related events, leading ultimately to the need for specific hardware to duplicate those events. Delay-related effects and the work of Haas are cited, and various early implementations of time-related signal processing are described. Tape loops, reverberation chambers, springs, and plates get their due before the discussion shifts to modern digital methods.
Studio implementation of time delay and reverberation are covered next, along with the role of delay in "correcting" the time anticipation in the use of accent microphones and in creating new sounds via "flanging." Further applications include generating chorus effects and creating phantom images by subtle signal delay. Concluding this chapter is a discussion of control-room acoustics. While this subject could have been dealt with in the preceding chapter, the author prefers to present it here, primarily as a caveat to users of delay-related signal processing. Woram's admonition is that early control-room reflections should not be so pervasive that they interfere with natural studio reflections picked up by the microphones. Only when the control room has been tamed, so to speak, can proper judgments be made and the signal properly processed with additional delay or reverberation.
The next area of signal processing deals with equalizers and filters. For most readers, this chapter will be a difficult one, inasmuch as it deals chiefly with theoretical considerations based on passive equalizer designs. Such designs have all but disappeared from the modern recording studio but still may be found in older re cording and sound-reinforcement equipment dating from the early '70s and before. In general, more space could have been devoted to applications and far less to theoretical considerations.
The next chapter covers the principles of signal compression and limiting in a very thorough manner. First, the need for dynamic range control is established, and manual methods are compared with electronic ones. The operating parameters of practical de vices are then defined and discussed. Noise gates (expanders) are covered, as is the combination of all three gain-control modes-compression, limiting, and expansion-into a single unit for "smart" hands-off gain control in a typical transmission channel. Specific application--such as de-essers, voice over compressors (duckers), and other frequency-dependent functions-are discussed.
The following two chapters deal with analog magnetic recording; the first goes into the basic recording process in great detail, while the second covers tape transport mechanisms from both the design and the operational points of view. It is the author's conviction that recording engineers will be working more with analog than with digital re cording gear in the immediate future, and thus the strong emphasis on the older technology. All of this makes sense insofar as there is more that a recording engineer needs to know about his analog equipment. With digital equipment, it either works or it doesn't; there is little-outside of keeping it clean-that can be done in the way of first-echelon maintenance. By comparison, optimum analog tape re cording is dependent on regular adjustment of many operating parameters.
The basic recording process is de scribed in terms of its essential non linearities, and the role of bias (a.c. and d.c.) in linearizing the process is then clearly presented. The dependence of distortion on bias, recorded wavelength, and record-head gap length is covered in detail, as are set up procedures for ensuring optimum performance. Tape erasure and print-through are also reviewed.
Magnetic-head losses are de scribed, leading to a discussion of tape equalization standards, reference levels, and high-output tapes. The chapter concludes with a detailed routine for playback and record alignment of a typical recorder.
The second chapter devoted to magnetic recording presents just about everything you might want to know about tape transports-including various drive and braking systems, tape path configurations, and control systems. Tape motion problems are discussed, both in terms of wow and flutter and long-term timing accuracy. Multi-track machines get most of the attention here, and the various functions of remote-control units in a nor mal studio setting are covered in de tail. Such procedures as automatic search, rehearse mode, punch-in/ punch-out, and track bouncing are clearly presented. The chapter ends with a discussion of maintenance and alignment of multi-track machines.
The chapter on noise reduction follows naturally, since NR is intimately involved with multi-track recording. The author describes all the current NR systems (as well as some no longer seen) in great detail, with graphs showing the effects of slight misalignments of the various systems. Even consumer-type systems are discussed, and appropriately so, since studio engineers are normally responsible for preparing the duplicating masters used in making cassette tape products. While studio noise-reduction systems are double-ended--i.e., they require processing in both recording and playback-single-ended systems (those that operate only during tape playback) are useful in a wide variety of transfer processes. Woram discusses these as well. Thorough cover age is given to Dolby SR recording, and the various NR systems are com pared. The author stresses the specific effects of calibration errors in the various systems, implying that the user should not treat them lightly. Many of these errors are small enough to go unnoticed, but alignment procedures should be scrupulously followed in order to maintain optimum performance.
The final major chapter deals with recording consoles. The discussion goes quickly through early evolution, concluding with the in-line console philosophy that is today's virtual de facto standard for multi-track recording. Woram's coverage of this type of con sole design is just about as complete as one could desire. For readers unfamiliar with this concept, the in-line con sole facilitates the one-microphone-per-track recording method central to many multi-track activities. In that re cording mode, the direct microphone output is fed to its destined track. All tracks are then monitored through an other section of the same input/output module, allowing these tracks to be auditioned as stereo program-complete with limiting, compression, equalization, reverberation, and everything else desired. The tracks that are being recorded are absolutely straight and are not affected in any way by the signal processing. The advantages here are creative freedom for the producer and the engineer, reserving all final musical decisions until later while allowing them to exercise interim options as they please. (In another mode of operation, the in-line console can function in the standard manner, in which all signal-processing options are reflected in the program signals going to. tape.) Final sections of the book present the basics of the SMPTE time code as well as an extended glossary.
The only subjects not covered are digital recording and console automation; Woram eschews the overview approach, and presenting these complex topics in any cursory way would not fit the mold of this book. Further, digital recording is well covered in many other publications, and console automation is developing so rapidly that documentation at this level can afford to wait.
Overall, Woram's new book presents its various topics with clarity, depth, and superb graphics. I highly recommend it to anyone involved in recording. Many of Audio's more technically oriented readers will also find this book informative, and to them, too, it is highly recommended.
-John Eargle
(adapted from Audio magazine, Dec. 1990)
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