Summing
Definition
The mathematical and electrical process of combining multiple audio signals into a single output. In digital audio, summing occurs internally in the DAW. Analog summing mixers are used to route digital tracks through analog circuitry, adding the harmonic character and headroom behavior of analog electronics.
In Simple Terms
Combining multiple audio tracks into one output. Your DAW does this digitally and perfectly. Some engineers prefer analog summing mixers for the subtle harmonic character analog circuits add, but the difference is subtle and debatable.
In Practice
An engineer routes the stems of a completed mix through an external analog summing mixer, preferring the way the analog circuitry handles the interaction between tracks compared to the DAW's internal summing.
Common Confusion
Analog summing does not automatically improve a mix. It adds analog character — which may or may not be desirable — and can introduce noise and calibration variables that require experience to manage.