Leveling the Sound Field

Some sounds are just too loud. What is too loud? It depends. The tonal quality of the sound, the background noise level; the condition of your hearing; the recent history of loud sound exposure; your relationship with the sound or its source;, can all be factors in what is too loud. Some sounds are just too quiet. Ironically, this is often for the same reasons.

I won’t give you a short course on hearing protection (this time). Instead, here are some thoughts on how to make soft sounds louder, loud sounds softer, and the way digital processing can improve the nature of dynamic processing without those mushy artifacts.

We have all heard the effects of massive dynamic processing on the tiny dynamic range of AM radio broadcasts and they are often using the best analogue gear. In live sound, we have been able to configure sound systems with over 100 dB of dynamic range for decades. All it takes is attention to detail. However, in spite of this vast range we can offer the performer, there are many opportunities to make improvements by controlling the dynamic range.

The noise gate was the tool of choice to achieve a wide dynamic range in sound reinforcement systems, although mic leakage may have been just as compelling. The noise gate can fix those less than perfect sources that bring humming, hissing, buzzing and late muddy sound from other instruments into the mix. It was the loss of the instrument’s attack that used to prevent using a gate to its maximum effect. The digital processor has allowed us to improve on this tool by offering to delay this troublesome input just long enough to open the gate before the attack of the sound. With a little time (a millisecond or two) to spare, we can now have the gate open fully at exactly the right time.

More difficult is the subtle reduction of overall dynamic range of a voice/instrument that is upfront in the mix. Digitally massaging the signal into shape can provide changes to the dynamics that only those that can hear the direct source in equal volume could detect (hint: these people are not in the audience). A daisy chain of analogue compressors would have been asking for more problems that it was worth. However, with the big DSP units available today, it’s no longer too noisy to place 10 compressors in a series/parallel configuration and finesse the sound source into just the right dynamic. This chain could include compressors with low thresholds and low ratios; compressors with side-chain EQ for pre-emphasizing the spectrum (to change the dynamics of vowels without affecting the consonants); limiters fed from crossovers (to allow the voice/instrument from becoming strident a higher volumes without ever sounding muddy); auto-gain that only operates over a narrow range where the instrument disappears from the mix; and delaying the sound through the limiter relative to the routing into the sidechain (to eliminate the pumping during heavy limiting on nasty bursts of energy). The result, a difficult vocalist no longer punishes the audience’s ears while you try to make his/her voice audible over the exuberant band.

These big digital boxes that offer a huge palette of audio tools in a few rack spaces, can bring this magic into the FOH mix. The luxury of mixing many cascading processors, with the innate ability to selectively add signal delay, should allow a whole new range of sound qualities to be realized in live performance. Integral to this signal processing capability is the ability to have controls that gang together the threshold settings on all the compressors in the chain and recall presets suited to specific parts in a song or set. The judicious use of a control (MIDI or low-voltage) interface will allow the units to accommodate the changes from one show to another. A thoughtful combination of processing and control mapping can make this complex processing chain as simple to use as a basic comp/limiter.

In the best conditions, sound reinforcement systems have long been able to outdo the dynamic range of all other audio systems. We have the power amplifiers available now to produce every last dB from the loudspeaker transducers. The loudspeaker systems can produce good audience coverage in both level and frequency response. There are venues with excellent ventilation systems, so that the music really can come from silence.

All of these things have the potential to combine and make live sound the most dynamic experience in our lives. We can now use this dynamic range artistically, to enhance the musical qualities of a live performance. Don’t simply recreate the signal path of your last analogue processing rack. If you have access to the DSP power, try creating something really dynamic. You may be able to get it exactly loud enough.

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