What Is Mixing and Mastering and How Do They Differ?

"I need someone to mix and master my song." You hear this phrase constantly. While the two processes are deeply connected, they are fundamentally different disciplines with different goals.

Here is the simplest analogy: Mixing is assembling the car. Mastering is the car wash and polish.

Mixing: The Assembly

Mixing happens after recording but before mastering.

• The Input: The mixer receives distinct individual tracks (Multi-tracks). Kick drum, Snare, Bass, Guitar 1, Guitar 2, Lead Vocal, Backing Vocal, etc.
• The Job: To balance these individual elements into a cohesive whole. The mixer makes creative decisions: "The vocal should be loud," "The guitar should be panned left," "The drums need more reverb."
• The Output: The mixer delivers a single stereo audio file (the "Mixdown").

Mastering: The Polish

Mastering happens after mixing.

• The Input: The mastering engineer receives one stereo file (the Mixdown). They usually cannot change the volume of the snare drum without changing the volume of the whole song.
• The Job: To enhance the overall sonic presentation. They focus on the "big picture." Is the overall tonal balance correct? Is it loud enough? Does it translate to other speakers?
• The Output: The mastering engineer delivers the final "Master" ready for Spotify, Apple Music, or CD.

Why separate them?

In the modern bedroom producer era, many people do both. However, traditionally they are separate for a reason: Perspective.

After spending 12 hours mixing a song, you lose objectivity. You get "demoitis" or ear fatigue. You might not notice that the bass is way too loud because you've been listening to it all day.

Sending the track to a dedicated mastering engineer provides a fresh set of ears in a different acoustic environment. They can catch mistakes the mixer missed. It is the final quality control step.