Recently, large format digital sound consoles have reached a sonic quality and functionality where they can easily be pressed into service for musical theatre sound. (It also seems to have reached critical mass in trade publications as articles on this development have been seen in ED and elsewhere.) Proponents typically rationalize that it doesn't matter if the new digital desk costs $400,000 as long as the money is recouped by selling those 20+ seats that a large format analog console typically removes from revenue. Are there tangible benefits to using a digital sound console for theatrical sound besides saving space at the mix position? Let me assist those of you who are on the fence by providing an overview of some of the considerations when going binary.
We'll skip over the usual arguments concerning reliability and redundancy and assume for a moment that our theoretical ideal digital desk is bulletproof. I often point out to people who worry that the digital console will go silent in the middle of a show that their speakers are likely processed via a DSP-based crossover. If that device quits during a show, things will get really quiet, really quickly.
Many specifications describe the sonic quality you can expect from a digital sound console, but sampling rate and bit depth pretty much define your digital world. The new standard for digital consoles is at least 96KHz — the audio is sampled 96,000 times per second. Look for a minimum 24-bit resolution as the benchmark with 32-bit or even 40-bit being featured for the internal processing. “Floating point” math versus “fixed point” math is something better left to the mathematicians and marketing gurus — both have advantages in certain situations. Keep in mind that for every 1-bit increase there is a doubling of the effective resolution of the signal.
After you have top-notch converters, expansive bit depth, and fast sampling rates, it is essential to ensure that the arrival times of the material are synced up. On a digital console this is usually described as being “sample accurate” meaning that at every stage where sources are combined within the desk, all of the signals are locked together perfectly. Digital consoles also require attention to delay management as every piece of digital equipment that manipulates audio introduces some degree of time offset. This latency may be something as small as a tiny fraction of a millisecond for an internal processing operation to several milliseconds for things such as converting audio into and out of the analog world. When using digital consoles and processing it is essential to keep track of system latency on the whole in order to avoid timing issues affecting the imaging or phase coherence of your sound system.
The sound that we have come to appreciate in Cadac and Midas consoles is in no small part due to the quality mike preamps, input and output electronics that they have engineered. Every aspect of a digital desk will ultimately be compared to the equivalent in analog, whether it is a “musical” compressor or gate, a “warm” EQ or the way that a certain mike preamp sounds when it is overdriven. Our ears appreciate the sonic signature of analog circuits and thus one of the key functions of a good digital console is to sound like an analog desk. The creative art of digital design comes into play as engineers attempt to model sounds in the digital world to emulate analog behavior. For example, Yamaha is now boasting a new technology known as Virtual Circuit Modeling where the very component level of a circuit is being synthesized digitally. This area continues to improve as higher sampling rates and greater bit depth allow for more transparent manipulation of the audio.
Wouldn't it be cool if all outboard devices could be replaced by the console DSP? We could even do this now if we use powered speakers and accept the effects packages resident in the new digital consoles. The reality is that many engineers and designers feel that these onboard effects cannot replace those favorite tube compressors or a top-flight reverb. Enter the world of plug-in technology. Digidesign has recently launched their Venue live sound-mixing environment which boasts a maximum latency from input to output of 2.8ms and the ability to use any Pro Tools TDM plug-ins. The biggest benefit of TDM plug-ins over the more generic RTAS or VST variety is their low latency achieved through tapping into the hardware DSP. Ideally all digital consoles would accept a standard plug-in so that any desk could have Sony Oxford reverbs or Focusrite compressors. Sadly, format arguments such as VHS vs Beta, SACD vs DVD-Audio, etc. have taught us that the idea of a universal plug-in technology will be elusive. Pro Tools is the only place where you are going to find TDM and for the moment, manufacturers other than Digidesign are developing their own proprietary “plug-in” technology.
The audio quality of analog is not the only thing that digital console manufacturers are striving to emulate. The interface for today's analog sound consoles has been around since rotary faders were replaced with linear faders and an experienced engineer who sits behind any analog desk will intuitively know how to adjust the preamp gain, the bussing, or manipulate the EQ. In the digital world, the only part of the interface that may look familiar is the actual faders, and even then it is likely that in certain operating modes these will handle the adjustment of some other parameter rather than volume. Studer's premise in designing the Vistonics interface for the Vista 8 live production console is that operators will always work more efficiently if the information of what is going on in the desk is closely aligned with the controls used to adjust the parameters.
Many feel that the biggest handicap with digital console technology is that a mixer needs to locate a parameter knob or button and then look at a TFT screen in a different location for a representation as to what that controller is doing. My personal experience has been that no matter what the interface, there will be a period of adjustment when first beginning to work with a new console. I would love to be able to design my own console interface based on the best features of the Yamaha PM1D and the DiGiCo D5 because, for me, there are great points to both ways of doing things, but neither one is perfect. Perhaps LCS, if you're leaving the analog world with its Cue Console, has this problem solved given the ability to individually tailor the console hardware control surface via the software. While this type of flexibility may suit some people, there is certainly a school of thought which says that the buttons, switches, and faders must remain consistent in terms of function in order for the interface to be operated by muscle memory.
Now that we have an imaginary reliable large format digital audio console featuring a rich analog sound, sample accurate transparent processing, a boatload of onboard effects and a workable interface, what else can this new technology deliver? To start with, digital desks are usually smaller and lighter than their analog counterparts leading to a decrease in required truck space, mix position real estate, and perhaps manual labor. Since optical, coaxial, and CAT5 cable can be used to transmit digital audio this reduces the heft and expense of copper cabling, not to mention lessening the likelihood of grounding issues. In turn, the architecture of most digital consoles lends itself to separating the input/output and even DSP components from the physical mixing desk. Multiple input and output boxes can be located close to the source with mike patch boxes near the band, outputs near the amps and so on. Digital consoles offer various forms of recall automation offering greater artistic freedom enhancing an audience's experience and flexibility when doing multiple acts, festivals, etc. Inevitably, digital offers the ability to completely program the functionality of the console scene-by-scene offline from a laptop, maybe in a hotel room. This same feature lends itself to wireless remote control of the console during production allowing adjustments to be made from multiple locations in a venue. There are many other advantages to using a digital sound console limited only by your creative imagination as the boundary between hardware and software becomes blurred.
Existing analog gear, which has been paid for, can often trump the latest, greatest technology when in the hands of the best creative minds. The choice of whether or not to jump into the digital mixer era will likely remain motivated by the price of theatre seats for some time, unfortunately. Meanwhile, digital audio consoles do offer some major advantages over analog and their eventual dominance in the field is assured. No matter what, let's make sure that our desire for new toys doesn't cause us to miss the point: A sound mixer's job is to creatively blend the music and vocals and to listen rather than getting bogged down in the operational details of a console, be it analog or digital.
David Patridge is a sound designer, production sound engineer, and audio consultant based in Toronto. Contact him at audioatelier@mac.com.
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