THE ART OF DIGITAL AUDIO RECORDING
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developers have become more and more sophisticated in their programming (and the computers have become more and more powerful, and thus capable of running complex, CPU-demanding software), a true debate about the relative merits of the two has arisen. Software developers have also taken to sophisticated modeling of analog units (often either with the blessing and aid of the original manufacturers or actually developed in-house by a software division of the original manufacturers). There is the additional matter of digital-to-analog conversion (and back again), which is necessary when using analog EQs on digital audio; this raises its own questions regarding the extent to which conversion might negatively affect the sound. And, of course, relative cost is often a factor as well, with the best software EQs costing much less than the high-end analog units. There is the additional benefit with software that separate instances of the software EQ can be used on many channels in the same session, while the analog unit is limited to a single use in any given session (unless its effect is recorded to a new track, so that it can be used again). Regardless of where one stands on the digital versus analog EQ debate, most agree that the newest digital EQs continue to sound better and better.
EQ and phase It is inherent in the nature of normal operation that applying EQ will alter the phase relationship of the sound that is being processed. This is because there is a certain amount of time required for the EQ to process the frequencies that it is acting on, and so those frequencies get shifted in their time relationships to other frequencies that make up the sound. This time shift creates changes in the phase relationship. Developers have found ways to minimize the negative effects that such phase shifting might cause, but it is not possible to eliminate the effect completely. As with virtually every kind of processing, there is a something sacrificed in exchange for what is gained. Using EQ will compromise the sound in certain ways, but it may enhance the sound in others. You need to balance the trade-offs. Recordists may speak about EQ in terms of decibels of boost and dip, and refer to certain frequencies with various Q settings or shelving characteristics, but to many musicians this will be meaningless. Finding the right nontechnical words to communicate about EQ and other recording qualities can be a valuable skill in managing the creative give-and-take of making recordings. (This is explored further in section 6.4).
Human hearing and the use of EQ When it comes to understanding EQ, it is valuable to consider the characteristics of human as controlled by the capabilities of the human ear. Two researchers defined these characteristics in 1933, and their description, known as the Fletcher-Munson curve, became the standard for understanding the biases of