I happen to be a firm believer in a low-input/high-output gain structure. I also realize that there is more than one way to arrive at a final live mix, and that it helps if one is not so intractable as to adhere to only one approach. I’m always interested as to how different engineers approach and set up their mix and, because of this curiosity, I found myself in a conversation with an engineer friend of mine who works in many different situations — from concert to corporate, in venues of varying size and structure.
He countered my low-input/high-output approach by saying the he likes to see as many bars as possible on the digital audio meter, since the signal is fuller and warmer the closer it reads to zero. Hmmm… it might just be that we sometimes overload on information, and because of this high input of facts and data, our thoughts become overloaded and distorted.
I remember way back in the final decade of the last century when Digital Audio Tape was a great way to record and store — not only data — but audio recordings as well. The thought was that for one to achieve optimal results, it was best to record as close as possible to the “0” mark on the recorder’s digital meter. In theory, this sounds like a viable idea, but the reality is that I would be given DAT’s to play as backing tracks and they would be distorted since they were recorded at “0” — or close to it — thereby leaving no headroom whatsoever for any peak program. Back then, of course, we were all still quite analog, and digital audio was still in its infancy, but the thing that quickly became apparent is that while there are certain audio distortions that are pleasing to the ear, digital distortion is not one of them.
The scale on a digital meter is known as digital full scale, or dBFS, and the meter shows the sample values of the digital audio signal. On the dBFS meter, “0” stands for the maximum achievable sample level, and any samples above “0” will cause “clipping” or distortion of the signal. As mentioned before, digital distortion is not a particularly pleasing sound, and to avoid such unpleasantness from occurring, we must set our digital meters differently than we set analog meters. The level used by television and radio that corresponds to the analog “0” is -12 dBFS, due to the compression used on the final mix, whereas post-production studios, which tend to be more dynamic in their mixes, refer to -18 dBFS as the “0” mark on their meters. A live mix has its own set of parameters that differ from either a media feed or a soundtrack mix, yet both of these levels work well as a “0” reference point when setting up for a live mix, as it leaves plenty of headroom while at the same time providing a strong enough signal to overcome any inherent noise in the console.
First Stage
A console preamp or head amp is the first stage of amplification for the relatively low voltage produced by a microphone or an instrument. This preamp not only affects the gain of the incoming signal, it is also instrumental in shaping the sonic quality of said signal. The analog signal coming into the console passes through an ADC, which converts the voltage from the analog input to a digital number, which then translates into an audio signal. Saturation is an analog phenomenon, and while there are now saturation plug-ins, the idea of turning up the digital mic preamp on a console to get saturation is not a viable idea. Granted, the more one turns up the preamp the stronger the signal becomes; however this is not saturation and does not “warm up” the sound. The noise floor on most consoles is very low, so not much preamp gain is required to overcome the signal-to-noise ratio. Also, as the preamp is turned up, the sensitivity of the incoming signal is increased, which means that a mic with a high preamp level is now picking up more extraneous noise coming from the surrounding area, which is why — in a live mix situation — I would suggest keeping a low input, while gradually increasing the gain in the output stages.
The solid-state preamp in a live console operates in a consistent fashion as the gain is increased with distortion kept at a minimum until the utmost level is reached — where clipping occurs. Console designers have spent long hours developing their on-board preamps and while many of these preamps function well and sound great, there are still those engineers who swear by tube preamps and insist upon having a few of them in their FOH rack. Many tube preamps on the market are in the hybrid category, which employ solid-state circuitry in the input stage for a clean, non-distorted sound and with a tube-driven output gain control to add the warmth of saturation.
Sweet, Sweet Distortion
While there is no hard-and-fast rule regarding preamps (especially since the advent of modeling preamps), tube preamps are known to be warmer and fatter-sounding than their cleaner-sounding solid-state cousins. This is due to the nature of the thermionic (valve) preamp, which produces a mild distortion as it heats up. This distortion is known as “Harmonic Distortion” and unlike the harsh distortion caused by clipping the digital preamp; some harmonic distortion artifacts can be quite pleasing to the listener. Even tone harmonics are the overtones of any given note, and if 100 Hz is the fundamental tone, then the following harmonics would be: 200 Hz even harmonic; 300 Hz odd harmonic; 400 Hz even harmonic; and so on. These even tone harmonics add color and depth to the primary tone and are what engineers describe as “juicy,” “fat” and “warm.” The highs seem more translucent and the mids more defined with an added low resonance in the bass.
Therefore, before you go bit-crushing your live mixes or adding digital distortion to any one channel, remember that there are many options available in regard to getting a full “saturated” sound. Other than having to carry a rack of outboard tube preamps, there are quite a few plug-ins that can warm up a vocal, instrument or final mix by providing the coveted harmonic overtones of a tube preamp. WaveArts Tube Saturator is one of the many plug-ins that can be used to get that warm analog preamp effect, while Neve 1073 plug-ins (from Waves, Universal Audio and others) emulate the extraordinary warmth and color of this legendary transistor preamp. For those seeking a different type of saturation, Crane Song’s Phoenix is a popular plug-in that models tape saturation and provides a few different settings depending upon the desired effect. So if you’re looking to fatten up your sound, there is no need to turn up your head amp to see more bars on the dBFS meter, since the audio the market itself is saturated with analog outboard and plug-in devices to help capture the warmth of days-gone-by. Now that’s saturation.
