What Is Audio Mastering? Mixing, Loudness and Delivery

Audio mastering is the final stage of preparing a finished mix for release. It involves listening critically to the complete recording, making any useful overall adjustments, checking the result and delivering files suited to the destination. For an album, mastering can also address how songs flow and sound together.

A mastering engineer usually starts with a stereo mix, though some projects use a small set of stems. The work is not simply making a song louder: it may involve small tonal or dynamic changes, quality control, sequencing and export decisions. iZotope's mastering overview describes these tasks and the distinction from mixing.

Mixing vs. mastering: what changes?

Stage	Typical starting material	Main decisions
Mixing	Individual recordings and instrument tracks in a session.	Balance the vocal, drums and other parts; adjust panning, effects and automation in context.
Mastering	Usually a finished stereo mix; sometimes agreed stems.	Assess the complete mix, make appropriate overall changes, check sequencing and prepare delivery files.

Both stages can use EQ or compression, but their input and purpose differ. If one word is too quiet or a guitar masks the singer, returning to the multitrack mix often gives more precise control. A stereo master affects a combined signal; it does not provide the original recording tracks. Read how to mix vocals for decisions at the earlier stage.

What does a mastering engineer actually do?

1. Listen and identify problems. Check the beginning, ending, transitions, clicks, distortion and tonal balance. If a problem is better fixed in the mix, request a revision rather than forcing a master-bus correction.
2. Make only useful adjustments. Depending on the recording, processing may include EQ, compression or limiting. Not every mix needs every processor. Match playback levels when comparing so that loudness alone does not make one version seem better.
3. Review level and dynamics. Measure loudness and peaks alongside listening. Heavy limiting can reduce transient impact or add distortion; a numerical target alone is not evidence of a good master.
4. Check the release as a whole. For multiple songs, compare transitions, spacing and perceived level while preserving intentional differences. Confirm the approved versions, titles and any delivery information required by the distributor.
5. Export and verify. Follow the recipient's current format and file requirements. Reopen the actual exports, listen through and check the start, end, channels and any required measurements.

Stem mastering uses agreed submixes instead of only a stereo file and can provide more control, but it is a separate arrangement with the engineer. Do not assume a source-separated estimate from a finished mix is identical to an original session stem.

How loud should a master be?

There is no universal loudness number that makes every song sound best. Streaming services may adjust playback levels, while other destinations have different requirements; normalization policies can also change. Check the current guidance for your actual destination and make a level-matched listening comparison before pushing a limiter harder.

Integrated LUFS describes measured loudness over a selection using gating; sample peak reports the highest decoded sample. They answer different questions. True peak estimates intersample peaks and is not the same as sample peak. Use a meter with true-peak capability if your delivery specification requires it. The peak vs. loudness guide explains why matching one does not automatically match the other.

For a short compatible file, Saturalabs' audio loudness meter measures integrated LUFS and sample peak locally. It accepts browser-decodable mono or stereo MP3 or WAV up to five minutes and 50 MiB, with at least 0.4 seconds of audio. It does not estimate true peak, process the audio or certify delivery. Measure the complete programme with a suitable full-length meter when the song exceeds those limits.

How to prepare a mix for mastering

1. Approve the mix first. Listen for vocal balance, edit clicks and unwanted distortion. Keep the editable project and note any concerns or alternate versions.
2. Ask for the engineer's requirements. Agree on file format, sample rate, bit depth, processing on the mix bus and any requested versions or stems. Do not apply an arbitrary peak target or remove processing that is integral to the approved sound without discussing it.
3. Export and check the file. Use the agreed lossless format, preserve the start and tail, and listen to the exported mix rather than assuming it matches the session. Do not expect a WAV converted from MP3 to restore discarded audio detail.
4. Send useful context. Share the intended destination, running order, approved mix and any reference tracks or specific concerns. Label versions clearly and retain the original export.

The WAV file inspector can show stored format fields for supported PCM or floating-point RIFF/WAVE files; it does not assess the quality of a mix. See how to check sample rate and bit depth for a practical walkthrough.

Can I master my own music?

Yes. Work from an approved mix, take a listening break, compare changes at similar playback levels and check the final export on more than one familiar system. If an adjustment makes a different section worse, revisit the mix or undo it. An independent engineer can bring another listening environment and perspective, which may be useful when the release matters or persistent problems are hard to diagnose.

Common questions

Does mastering fix a bad mix?

It may improve an overall issue, but it cannot reliably rebalance individual sources or restore detail that was never captured. A revised mix or cleaner source is often the better fix.

Is mastering just compression or normalization?

No. Compression and level adjustment are possible tools; mastering also includes listening, decisions about the release, quality control and preparing suitable delivery files. Some mixes need very little processing.

Do I need to master a single song?

A final listening and delivery check is useful even for one track. The amount of processing and whether to hire an engineer depend on the mix, destination, budget and goals.