What Is Mixing and Mastering?

Mixing: assembling the parts

A recording session for a band might produce 30 or more individual tracks: kick drum, snare, hi-hat, bass guitar DI, bass guitar mic, rhythm guitar (left), rhythm guitar (right), lead guitar, keyboards, lead vocal, backing vocals... and so on. Each of these tracks was recorded separately and each sounds disconnected on its own.

Mixing is the work of making all those parts sound like one cohesive performance. That involves:

• Level balancing — deciding how loud each track is relative to the others
• Panning — placing elements in the stereo field (left, right, centre)
• EQ — shaping each track's frequency content so they coexist without clashing
• Compression — controlling dynamics, adding sustain, gluing elements together
• Reverb and delay — adding space, depth, and atmosphere
• Automation — changing levels, effects, or parameters over time as the song progresses

The output of mixing is a stereo mix file — typically exported as a 24-bit WAV at the project sample rate, before any final limiting is applied.

Mastering: preparing for the world

Mastering receives the stereo mix and prepares it for distribution. The mastering engineer listens to the mix on speakers they know extremely well and makes adjustments to ensure the record translates correctly across different playback systems — from earbuds to car speakers to nightclub sound systems.

Mastering typically involves:

• Broad EQ adjustments — fixing problems with the mix's overall frequency balance that weren't apparent during mixing
• Multiband compression or limiting — controlling the overall dynamic range
• Loudness targeting — bringing the track to an appropriate level for its distribution platform (streaming, CD, broadcast)
• True peak limiting — ensuring no inter-sample peaks exceed platform limits (-1 dBTP is the streaming standard)
• Dithering — adding low-level noise when reducing bit depth (24-bit to 16-bit) to prevent quantization distortion
• Sequencing — for albums, ordering tracks and setting the gap between them

Why they're separate jobs

The separation exists for practical and perceptual reasons. Mixing is a detailed, close-focus task — the engineer spends hours or days inside the individual elements. After that much time, the ear loses perspective on the overall picture.

A mastering engineer comes to the mix fresh, with no attachment to the decisions made during mixing. They hear the sum with objective ears. They also typically work on speakers with a well-established reference point — they know exactly what a "correct" mix sounds like on their system, which makes them very good at spotting what the mix still lacks.

For home recordings and independent releases, one person often does both — but with a significant gap between the two sessions. Mastering your own mix immediately after finishing it is the worst of both worlds.

What mastering cannot fix

Mastering is not mix repair. It's a last-pass refinement, not a substitute for a well-executed mix. A mastering engineer working with a stereo file cannot:

• Pull down a vocal that's too loud relative to the backing track
• Remove a frequency problem on just the bass guitar without affecting everything in that range
• Fix clipping that happened in the mix
• Add reverb or effects to individual instruments
• Correct timing issues between tracks

This is why mixing matters so much: mastering amplifies the mix's character, for better or worse. A great master of a poor mix is still a poor recording. A great mix needs very little mastering work.

The mix file format question

When sending a mix to a mastering engineer, always export a lossless file — 24-bit WAV or AIFF at the project sample rate. Never compress a mix down to MP3 before mastering; the lossy encoding introduces artifacts that become more noticeable after the limiting and level increases applied during mastering.

The final mastered file delivered for distribution will typically be a 16-bit/44.1 kHz WAV (for CD or streaming) or a 24-bit version for streaming platforms that accept it. The loudness level will depend on the target platform.