Though the variety of audio processors out there seems vast, the actual number of audio processes they employ is much smaller. In the realm of sound systems, most audio processing is accomplished with just a few basic building blocks. Give a talented engineer or system designer control over enough of these basic processes, and he or she can do virtually anything needed to really dial in a sound system.
This “building block” approach is at the heart of Architectural Acoustics’ Digitool Programmable Audio System Processor ($1,700 list price). Between input and output, each signal may pass through more than 20 distinct audio processes or blocks. Consider that this processing is happening across eight inputs and outputs at squeaky-clean 32-bit resolution, and it becomes apparent that the Digitool must have some serious horsepower under the hood. It does, in the form of two SHARC processors delivering a combined 132 million instructions per second (MIPS). Latency (delay between input and output) is a scant 1.5 milliseconds, and will not increase as more processing blocks are used.
Input to Output
The Digitool offers eight balanced analog inputs and eight balanced analog outputs (no digital I/O). Inputs will accept line-level signals covering a broad range of nominal levels, as well as mic signals. Being able to plug a mic directly into this type of processor is almost unheard of, yet the Digitool goes a step further to supply phantom power for condenser mics. In some applications, direct processing of mic signals is the perfect solution.
Once past the converters, signals progress through a fixed order of processing blocks. Whereas a fixed effects order would never work for a guitarist’s stomp boxes, it’s not much of a liability here. The order of processes inside the Digitool makes sense for the vast majority of sound reinforcement applications.
After initial gain is set, input signals hit their first of many Digitool filter blocks (it has 96 total). The Digitool offers 12 different types of filters including gentle high- and low-pass; parametric and shelving EQ; band pass and band stop; horn EQ and several more. Many of the filters offer a Q control, which makes them all the more flexible. Increasing the Q parameter on a filter in moderation can add a useful bass boost at the high-pass frequency, or gentle treble lift at the low-pass frequency.
Next up is the Digitool’s noise gate, which offers a full complement of adjustable parameters. These include threshold; attack, release and hold time (each spanning 1 ms to 1000 ms); and attenuation. Attenuation lets you control how much gain reduction is applied to signals below threshold, and it’s a critical parameter for achieving unobtrusive gating.
Input signals then pass through four more filter blocks, each selectable from the same 12 filter types. A compressor block is next, offering threshold, ratio, gain and attack/release time controls. The final blocks before the Digitool’s matrix mixer offer control over channel trim (attenuate only) and phase. The Digitool’s matrix mixer sits at the midpoint of the signal’s journey, allowing any input to be routed to any output at any level.
Once through the mixer, output signals hit a band-pass crossover filter. This filter offers Butterworth, Linkwitz-Riley and Bessel types, each with several slopes. Next up is a series of seven individual filters, each selectable from one of the 12 available filter types. An output compressor follows the filters, offering the same controls as the input compressor. Next is a delay offering up to 5 seconds of delay time. The delay’s coarse adjustment is in milliseconds, while a fine control makes adjustments at microsecond resolution. This level of accuracy allows for precise time-alignment of anything from individual components in a speaker to whole stacks or arrays.
Last in the output signal chain are controls for overall output level, metering and phase.
The Digitool offers a few other processor functions worthy of note. One is a priority override system for the first input that allows its signal to reduce the level of other selected channels. Attach a mic to input 1, select the channels to be overridden, and the Digitool will automatically reduce the volume of background music or sound in response to the mic input. A separate automix feature uses the popular NOM (Number of Open Mics) process to reduce feedback in high-gain situations. NOM monitors the number of inputs receiving signal (mics, in this case), reducing input gain as the number of active inputs increases. Up to four separate automixers can be used across any combination of input signals. vi
In the utility department, the Digitool offers a useful signal generator whose signal can be sent to any output at any level. Test signals include sine wave with adjustable frequency, white noise or pink noise. The generator inserts its signal just after the matrix mixer, which then passes through all output processing. Such a signal generator is seen by many engineers as a must-have for fine-tuning or troubleshooting any sound system.
The Digitool’s designers were literally thinking “outside the box” when they developed several different ways to control the Digitool remotely. Architectural Acoustics’ D1V and D4S serial remote controls mount in the wall like a single- or double-gang light switch, connecting to the Digitool by regular CAT-5 (Ethernet) cabling. Up to 31 of these controllers can be attached to the Digitool. The D1V’s volume knob position can control virtually any level from input to output, while the D4S has four switches that can either recall the Digitool presets or toggle individual signals on or off.
A second remote control system uses standard potentiometers (rotary knobs) to control levels within the Digitool. Up to four of these simpler CV (control voltage) remote controls can be attached and mapped to various gain settings. In combination with the serial system, the possibilities for remote control of the Digitool are almost endless.
The Digitool offers an RS-232 serial port for connection to a computer. This allows point-and-click setup of all parameters using Architectural Acoustics’ excellent Digitool Designer software, as well as easy upgrades of the Digitool’s own internal software. A recent software update allows a single computer to control and monitor up to eight Digitool processors by TCP/IP over Ethernet cabling (the common networking protocol used by most computers). Finally, in a significant gesture towards compatibilty and integration, the Digitool will respond to AMX or Crestron controllers.
Four Is Enough
Every product designer faces a challenge when it comes to giving the user effective control over their device. The more powerful and versatile the device, the more crucial the human interface becomes. The Digitool is certainly no exception to this rule—a product this powerful and complex lives or dies based on the quality of its interface.
Instead of a large number of dedicated controls and displays, Architectural Acoustics designers opted for just four multi-purpose knobs surrounding a backlit LCD on the Digitool’s front panel. Metering is also simple, with a single dual-color LED for each input and output. These LEDs show signal present and signal peak.
The Digitool’s interface consists of numerous screens navigated with the large PROGRAM knob. On these screens, most parameters are then adjusted—with changes heard in real time—with the three smaller knobs. I’ve seen similar interface schemes that were a maze of confusing, counter-intuitive screens and functions. Not so with Digitool—its interface is well-conceived and intuitive, and should make sense to most users within the first few minutes.
Beyond its effective layout of screens and functions, the Digitool’s interface has several nice touches. For example, the Digitool remembers the screen (or block) you were last on when you return to an input or output channel. Where possible, the Digitool makes routing and setting up signal flow simple. Click on an output channel in the RouteView window, and a pop-up box lets you quickly configure a two- or three-way crossover across adjacent outputs.
A Matrix view lets you quickly map inputs to outputs, adjusting levels from the same screen. The Digitools’ notes editor allow each preset to be annotated with text, which would go a long way towards orienting a new operator on the specifics of a given setup. In all, the Digitool’s interface is about as good as it gets.
It’s fortunate that the Digitool’s interface is top-notch, because its manual leaves much to be desired. Clearly many software versions behind, the Digitool manual covers just a fraction of the processor’s features. Advanced topics like NOM and remote control setup are nowhere to be found. Instead, you’ll see these topics addressed only in the Windows help file of the Digitool Designer software. The folks at Architectural Acoustics are reportedly working on a long-overdue QuickStart guide for the Digitool.
In Use
Once you get your bearings, setting up the Digitool is a straightforward affair. The four-knob interface offers smooth, predictable control. That said, changing some parameters can make for a lot of knob twisting (some parameters require more than 100 clicks to span their full range of values). Too bad the knobs don’t kick into a non-linear “high-speed” mode when required.
The LCD display is sharp and bright, and has an adequate refresh rate. The display’s only shortcoming is that it’s set back about 1/4-inch from a rather skimpy display window, which means you have to be directly in front of the unit to read the display. Moving even a few inches off-axis means losing the edges of the LCD.
Sonically, the Digitool earns high marks. Signals stay clean and transparent through the unit, with no discernible artifacts. The Digitool’s 24-bit converters sound very good on input and output, and the unit’s analog electronics offer excellent specs in the audible band. The Digitool offers sampling rates up to 96 kHz, but I never figured out how to adjust its sample rate—even with the software help file.
The Digitool’s filters sound excellent across the board, offering the kind of purity and precision engineers will appreciate. The gate is very well-behaved overall, with no clicks or glitches even at its fastest attack time (1ms). The Digitool’s maximum gate release time is one second, which is on the short side for some applications.
The compressor also sounds very good when properly set up, controlling gain without pumping or other artifacts. It offers a full range of parameters and no “auto” settings, so some prior knowledge is required to get desired results. The Digitool compressor will “fake it” as a limiter, but its 1 millisecond minimum attack time and lack of infinite gain reduction keep it from functioning as a true brick-wall limiter. Frankly, I’m surprised the Digitool doesn’t offer a limiter block in addition to the compressor.
Another surprising omission is a way to link compressor or gate channels for stereo operation. Running stereo audio through two unlinked mono compressors or gates, as the Digitool forces you to do, can spell shifts in the stereo image. Nor does the Digitool offer any way to simultaneously control parameters (EQ, for example) for stereo channels. Hopefully, a future software upgrade will properly address stereo processing.
Power Tool
A few omissions aside, the Digitool stands as an impressive tool for controlling and processing sound in live applications. In the hands of a capable engineer, the Digitool could make significant improvements in the sound of most house systems. Beyond that, the Digitool has the potential to optimize signals to feed in-ear monitors, zone systems, hearing assist systems, duplicators, recorders and much more. Add in its remote control capabilities, and the potential benefits of this versatile box extend even further.
If your house of worship has places where the quality, level or availability of audio signals is not what it should be, the Digitool probably has what you need to fix the problem. If you can conceive it, odds are good that the Digitool can do it.
Loren Alldrin is a regular contributor to Church Production Magazine.
