SIDEBAR TO "FUTURE OF DIGITAL MIXING"
When Brian Blackmore at Church Production asked me to write about why an engineer should consider using an external preamp alongside a digital mixer, I decided to ask some of the engineers we work with to get their opinion on the subject. The following article includes input from Paul ‘Pab' Boothroid (Paul McCartney), Dave Natale (Rolling Stones), Derek Williams (Bonnie Raitt), Jim Warren (Radiohead), Michael Davis (Dolly Parton), and Jim McCullagh (Journey).
The general opinion is that digital mixers are getting better all the time. The real advantage they bring to the table is convenience. So using an analog desk, or going a step further by incorporating analog preamps, usually comes down to paring the sound of the device to the artist's sonic signature, the engineer's personal preference or a desire to recreate the exact signal path that was used during a particular recording.
External mic preamplifiers have a huge advantage over mixing consoles in that they have the space inside to incorporate full-sized discreet parts, tubes and transformers. More space generally means a lower noise floor, as spacing the parts usually results in less bleed due to electromagnetic induction. These “big parts” also impart second-order harmonic distortion that we interpret as a “warm analog sound.” When devices like transformers are driven hard, they do not distort in the same fashion as a chip. They round out the peaks like a very subtle limiter producing the vintage tone we love. And with so many artists now using in-ear monitors, they are enjoying better quality than ever before. This makes them all the more aware of what sounds good and what does not.
For the live engineer, the attraction to delivering the very best sound must be balanced against convenience and cost. Carrying a rack of 48 separate mic preamps is great in concept, but practically impossible. In fact, the only time this is done is when the artist is planning a live recording. By having high-quality mic preamps on stage, one can benefit from lower noise, improved character and, of course, maximize the performance when using better mics on stage such as studio condensers. As a compromise, many engineers carry one or two mic preamps for the principal artist(s) on stage. This enables the engineer to deliver the sound that the artist expects, while retaining the convenience of the digital console for the rest of the band.
This also presents another advantage in the form of consistency. For bands that travel from one venue to another, the engineer may be presented with a console of dubious quality or one that he or she simply does not like. Having a couple of good-sounding mic preamps on hand ensures that the principal artist will be delivered a familiar sound in their monitors each night and it will eliminate some of the unknowns for the audio engineer. Familiarity usually means getting the job done faster, which of course means getting to eat dinner before the show.
Today, there are hundreds of quality mic preamps to choose from. These can come in the form of full-sized Neve or Avalon 19-inch rack devices, or today's more compact 500 series lunchbox-style units. The latter presents a compelling advantage whereby one can mix and match modules to create the ultimate channel strip. Using a small three-module 500 series rack, you could, for instance, combine a Radial PowerTube preamp with an API equalizer and a Neve compressor to deliver a particular sound. Or if multi-track recording, you could use a larger rack to gang together a number of mic preamps and pack them into a very small space.
Incorporating external preamps is normally done by connecting the mic to the preamp and then plugging the preamp output to the line input of the digital mixer. If multiple external mic preamps are being used for a live recording, then the signal will usually be split on stage using a high-quality, transformer-coupled splitter that will send the mics to both the PA and the recording system. Transformers help eliminate the hum and buzz caused by ground loops, which will result in a quieter recording. This also enables the recording engineer to control the input coming right off the stage microphones without interfering with the house PA requirements.
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