From Digits to Digital
Exhorting the virtues of Digital Signal Processing (DSP) for today's house of worship

By Dr. Robert McPeek

In ancient times, when black-and-white television was new, with a paltry three or four broadcast channels to choose from, control of program selection was "digital"--meaning the channel knob required manual switching with the digits of one's hand. Fifty years later, television has gained color, cable and satellite (100+ channels) programming, picture-in-picture viewing, programmable VCRs, and even built-in video recording. The get-up-and-turn-by-hand method of control has been replaced by another form of digital control: wireless, digital remote control channel and function selectors with keypads and menu options that leave the TV audience comfortably ensconced on the couch.

In parallel fashion, similar changes have occurred with audio systems and the means by which sound is shaped and controlled. The ancient single-microphone-amp-speaker configuration no longer fits the many needs of the modern house of worship. At one point in history, the defining purpose of a sound system was simply amplification. More recently, the level of sophistication for worship sound has improved exponentially, encompassing not only state-of-the-art sound reinforcement for house and multiple monitors, but recording and broadcast mix splits as well. And, like any technology of the new millennium, the audio tools of choice increasingly harness the impressive power of digital signal processing, or DSP for short.

For years, audio engineers have processed and manipulated sound in the analog realm--meaning the complex waveforms of audio are represented (usually) by an electrical replica, with voltage varying in direct proportion to fluctuations in air pressure created by a sound source. Digital audio, the new kid on the block (though the kid is now pretty mature!), represents sound in an entirely different way. Essentially, digital audio is a series of measurement samples of audio, stored in binary code--the generation of a huge sequence of zeros and ones in a process called "analog to digital conversion." After being digitally stored, recalled, modified and so on, the resultant binary formula can be mathematically decoded to recreate the original audio. The manipulation and modification of audio content that takes place while the audio is digitized is referred to as DSP.

There are two broad categories of DSP equipment offered for sound system operation. One category--including equipment like equalizers, speaker alignment delays, compressors and even mixers, addresses the "nuts and bolts" of sound system operation, offering tools designed to make the presence of sound equipment as transparent as possible. In the best application of such equipment, the technology disappears from the audience's awareness. In contrast, the second category of DSP products, including processors like reverb, echo, flanging, chorusing and so forth, is designed to enhance or intentionally alter amplified sound, often used quite obviously and deliberately as an effect.

Since not all sound systems require such effects processing but all good sound systems aspire to transparency, our focus here will be restricted to DSP tools designed to operate unobtrusively. There are four major categories of such DSP:

1. Compressor/limiters help control the dynamics of sound reinforcement. Compressors are useful to restrict huge variations in mixer input levels to a more controllable range--compensating, for example, for speakers or singers who both shout and whisper into microphones.
2. Digital delays help synchronize the arrival of sound from multiple sources to a listening location, thus minimizing selective cancellation and/or reinforcement of audible frequency bands, with a net improvement in response linearity and clarity.
3. Equalizers, as the name suggests, are designed to even out variations in frequency response that arise as a function of the equipment used, and the acoustical properties of the listening environment.
4. Mixers, which are designed to blend sound from a number and variety of sources (open microphones, pre-recorded CDs or tapes, audio from video and more) into a single balanced output, typically called "the mix."

Such simple categorization is complicated by the ease with which DSP equipment can perform multiple functions; i.e., one unit may compress, delay and equalize, or a mixer may offer built-in compression on its input channels.

All of these products have their analog counterparts, often the culmination of years of development of a proven technology. Given this option, what are the compelling reasons for considering digital processors over analog ones? There are a number of significant advantages:

1. New levels of precision and control. Analog equipment offers a signal path that passes audio through physical components. These components are more susceptible to aging and wear and also to manufacturing variations in component parts. In contrast, DSP products use circuit parts only as architecture for a digital processor, which works in binary code. Once a signal is digitized, it is no longer susceptible to component physical wear and tear.

Moreover, a digitized signal lends itself to easy storage and recall, freeing the sound engineer from the ancient, tedious practice of recording the position (however inexactly) of every knob on an analog box. To the delight of sound engineers everywhere, a digital mixer, as an example, can save several completely different configurations of fader levels, EQ settings and more, and switch back and forth between presets quickly and accurately.

A final enhanced degree of precision is afforded by DSP components that offer some method of displaying parameter settings. On an analog box, you can point your compressor gain to 10 o'clock. With a digital box, you can get readout of the exact gain (e.g., -4.5 dB).

2. The power of the multiple-function box. The ultimate symbol of the digital age--the computer--has become ubiquitous in large part because of its versatility. It is used in a mind-boggling variety of business activities, from pure number-crunching applications such as accounting, to recording and editing audio and video. In like fashion, audio DSP products often combine a multitude of functions in a single unit. Once a signal enters the digital realm, further processing to the signal is a matter of software, not hardware. This means an enormous gain in the scope of what a single DSP box can do, and a corresponding decrease in the number of components, cables, power supplies and current draw, and rack space needed to achieve similar results with analog processing.

3. Cost savings. If you follow old world economic theories, you'd expect such an increase in features to come with a corresponding increase in cost. However, in the 21st century, with the rapid ongoing development of digital processing, the opposite has happened. There is usually a tremendous cost savings to be realized with DSP products, which is particularly impressive when you compare features per dollar. Add up the cost of a stand-alone compressor, graphic EQ, parametric EQ, feedback controller and delay, then compare that to the cost of a digital box that does all of these things (in far less rack space as an added bonus), and you'll be glad you were born in such a wondrous age.

4. Convenience. One DSP box that does the work of four or five other products is a great way to save wear and tear on your most important piece of equipment, your own body. But the benefits of DSP are more than just physical. Nice operational features, such as password protection (to prevent unauthorized tampering with your settings); computer networking (which allows multiple units to be controlled from one computer, sometimes even off-site); user customization and more mean that you can personalize a piece of equipment to suit your own preferences. Plus, you can recall those preferences at the push of a button.

5. Keeping up with the latest technology. We have all experienced the thrill of buying last year's state-of-the-art equipment sold as the latest and greatest, leaving us stuck with a piece of gear with a limited future. DSP has a very important advantage over analog products in keeping your equipment up-to-date. Since DSP boxes are software-driven, they can be easily updated with new software versions as the manufacturer releases them. Such an update can take the form of an EPROM plug-in, or even as a Flash RAM update that can be downloaded from a manufacturer's Web site. Often, these upgrades are inexpensive or free to registered owners.

Is there a downside to DSP? Of course. Any new technology offers some advantages, but gives up something in return. Audio engineers all have an opinion on their favorite pieces of gear (just ask one and stand back), and there will always be debate about the sonic integrity of analog vs. digital audio (tubes vs. transistors, vinyl vs. CD, VHS vs. Beta, Yankees vs. Mets, and so on). In the absence of any hard data clearly supporting any particular point of view, there remains one feature where analog maintains a diminishing advantage: the familiarity and user-friendliness of analog processors. Many powerful DSP products are menu-driven and more difficult to use, compared to the tried-and-true, plug-and-play nature of our favorite analog warhorses. But even this is changing as some DSP devices give users front-panel, analog-style control of digital signal processing.

As the cost and feature advantages of digital slowly change the way audio is shaped and amplified, sound technicians can benefit from more, not less, choice of processing equipment. Before you know it, you'll have the option of using your wireless modem controller to set up and mix the church audio while you sit at home--comfortably ensconced on your couch, of course.

Dr. Robert McPeek is the Export Manager for Sabine, Inc. Dr. McPeek is responsible for on-going development and improvement of Sabine's high-end DSP line, including the GRAPHI-Q 31-band digital EQ, FBX Feedback Exterminator^®, compressor/limiter and digital delay. As owner of Mirror Image Studios in Gainesville, FL, he logged over 20 years as producer-engineer-musician and has recorded Parliament-Funkadelic, Sister Hazel, Bo Diddley, Joan Osborne, and River Phoenix, among thousands of artists and songwriters. Contact Dr. McPeek at (904) 418-2000 or e-mail him at bmcpeek@SabineUSA.com. Visit the Sabine Web site at www.SabineUSA.com.