Audio Summing Explained
In the Early days of recording, music was cut directly to a disk from a single microphone. In the studio, the art of mixing fell to the music “Conductor” whose job it was to move the musicians who were recording either closer or further back from the microphone.
By the 1930’s the radio broadcasting industry developed three and four channel tube-based mixers to sum multiple microphones into a mono signal. They also developed line mixers to combine pre-amplified signals with music from turntables for on-air programs. These early tube mixing consoles from RCA, Western Electric, and GE were built as boxes that sat on a tabletop. This provided easy access to basic switching and leveling controls. In those days the levels were done with large knobs instead of the familiar modern sliding faders (Thank you Tom Dowd!) . These boxes provided routing, balancing, and a master level control, but for the most part, the microphone amplifiers, compressors, and other equipment that was needed by the console would be mounted in additional racks.
In 1953 the legendary “Les Paul” developed the first 8 track tape recording system, which was later produced by Ampex. This revolutionary development ushered in the modern recording era. In a short time we went from 8 tracks to 16 and finally 24!
Starting from the early days of mixers, the engineers and designers were always striving to achieve the perfect blending or “Summing” of those multiple channels first into a mono signal and later stereo, quad and finally surround sound. With each new generation of mixing consoles, engineers worked to create the perfect “summing” circuit.
The problem came with the fact that no matter how well you design the circuits the components still had variations in their performance and tolerance. Even with the most expensive mixing consoles, no two channels were exactly the same. As they aged their responses and tolerances would change over time, and change their sound and character. No matter what they did there was a ceiling to what could be done with analog summing, and the perfect mathematical combining of multiple audio sources remained elusive.
When Digital Recording became prominent in the industry the realization of the “Perfect” summing of multiple audio sources became a reality. It now became a function of a mathematical equation that combined the multiple sources into one mix.
ANALOG VS DIGITAL SUMMING
As DAW software got more sophisticated, and more plugin companies began to successfully model many of the legendary analog compressors, EQ’s as well as other gear that was in the racks of the top studios of the 60’s and 70’s, it gave rise to many engineers deciding to “Mix in the Box” or use the digital summing engines in their DAW’s.
Other engineers felt we lost that “color and character” that the mixing consoles gave to the music. They believed we needed these multiple “imperfect” channels combined in the less than perfect analog summing circuit. These recording engineers took the output of their DAW’s and routed them through their mixing consoles and recorded the output “Summed” mix back into their DAW. Later this gave rise to “Analog Summing” units that performed the single function of summing. Companies such as Dangerous Music , Neve and SSL to name a few. Unfortunately these are very expensive and out of reach of most home studios.
Ian Vargo created an experiment on listeners perception between analog and digital summing. Interestingly Classical music listeners preferred digital summing while rock listeners preferred analog. Then you have the country and pop listeners which really didn’t have a preference.
Many of the plugin companies like Waves, UAD, Slate Digital to name a few have created “Summing” and “Console” emulation plugins to simulate analog summing. For those who wish to still “Mix in the box” these are a good alternative to Analog Summing.
ANALOG MIXER SUMMING
If you already own an analog mixer, you can use this as an inexpensive (only because you already own one) way to incorporate analog summing in your studio. If you have multiple outputs on your AD/DA converters you can feed those outputs into your mixer and route the main mix buss back into your DAW or have a secondary computer with a DAW to record the resulting mix.