What online mastering actually does
Mastering is the final stage between a finished mix and a released track. It sets the overall loudness, balances the tonal curve, controls the peaks so the file survives lossy encoding, and makes sure the record holds together across headphones, car speakers and a club system.
An online mastering service moves that work off your desk. You upload a mix, the platform applies a processing chain, and you get a master back. What differs between services is how much of that chain you can see, how much you can change, and what the result actually measures.
Two things are worth separating early. Automatic mastering applies a chain without you deciding anything. Assisted mastering gives you targets, metering and controls, and lets you make the calls. Both are legitimate; they suit different people.
The measurements that decide whether a master works
Before comparing services, it helps to know what a master is judged on. These are the numbers every platform is implicitly targeting, whether or not it shows them to you.
Integrated loudness (LUFS) — measured to ITU-R BS.1770. Spotify, YouTube, Tidal and Amazon normalise playback to roughly -14 LUFS; Deezer sits one unit lower at -15; Apple Music targets about -16. Going louder than the reference does not make you louder on playback — the platform turns you down, and you keep the dynamics you sacrificed.
True peak (dBTP) — the real peak level after the signal is reconstructed, including the inter-sample peaks that a normal peak meter misses. Streaming wants -1 dBTP; video delivery specs such as Netflix require -2 dBTP. Overshoot here and lossy encoding produces audible distortion.
Dynamic range — how much space is left between the loud and quiet parts. A master crushed flat measures loud and sounds tiring. This is the single most common failure in amateur masters, and no service can restore it once it is gone.
The services, compared honestly
Here is where each major platform actually sits. Features and pricing change, so treat this as a starting point and check each site before you commit.
LANDR — one of the original AI mastering platforms, and the most complete package: mastering plus distribution to stores, plugins and sample libraries. The free tier lets you preview a master but not download it. Choose LANDR if you want mastering and distribution from one account.
eMastered — founded by Grammy-winning engineers, with reference-track matching and a familiar set of engineer-style controls. Also preview-then-pay. Choose it if you like turning knobs and want a traditional mastering-console feel.
BandLab Mastering — genuinely free, with unlimited downloads and no watermark, which is unusual and worth saying plainly. It applies preset chains with little control and no published metering. Choose it when you want a fast, no-cost result and do not need to hit a specific target.
CloudBounce — often recommended for electronic and hip-hop, with a budget-friendly position. Preview-then-pay like most of the category.
Waves Online Mastering — from a long-established plugin company, with a deliberately minimal workflow and a short preview before you commit.
MasteringBOX — a browser-based option with a free tier, aimed at quick results.
Quantara Music — ours, so treat this paragraph with the scepticism it deserves. The chain runs in your browser, so the audio is never uploaded for mastering. Every stage is visible and adjustable, the metering is real BS.1770, and the free tier includes three genuine WAV downloads a month with no card. It is deterministic DSP, not a model — the same input always produces the same output. We do not offer distribution, so you would still need a distributor.
Free tiers: what “free” means at each service
The word free covers two very different things in this category, and the difference matters more than any feature list.
Preview-only — you upload, hear the master in the browser, and hit a paywall at the download. This is the most common pattern and it is not dishonest, but it is worth knowing before you invest time.
Free download — you actually keep the file. BandLab does this with no limit. Quantara does it with a monthly cap. If your goal is to release a track without paying, only this category helps you.
A watermark is a third variant: you can download, but the file has an audible tone or voice over it. Check for this before assuming a free download is usable.
How to choose, in practice
Start from what you need rather than from a feature table.
You need it released today, at no cost. BandLab — unlimited free downloads, no card.
You want mastering and distribution in one place. LANDR.
You want to hit a specific loudness target and verify it. Pick anything that shows you real LUFS and true-peak numbers. If a service does not publish its metering, you cannot check the result.
You care where your audio goes. Browser-based processing means the file is not uploaded to a server for mastering. Read the privacy policy rather than the marketing.
You are mastering AI-generated music from Suno, Udio or Mureka. These tracks have characteristic issues — low-mid build-up, harsh upper mids, inconsistent loudness between generations — that reward a chain you can adjust rather than one you cannot.
Questions worth asking any service
Does the free tier let me download the file, or only preview it?
Does it show real BS.1770 loudness and true-peak numbers, or just a loudness slider?
Can I hear the difference at matched loudness? Anything sounds better when it is louder — A/B comparison is meaningless without loudness matching.
Is my audio uploaded to a server, and how long is it kept?
Can I adjust the result, or only accept it?
Does it export lossless? A master delivered only as MP3 is not a master you can send to a distributor.
Frequently asked questions
It depends on what “free” needs to mean for you. BandLab Mastering is free with unlimited downloads and no watermark, which is the most generous free tier in the category. Quantara includes three free WAV downloads a month with real metering and an adjustable chain. Most other services — LANDR, eMastered, CloudBounce — let you preview for free but require payment to download.
For a well-made mix, a good online master can be close enough that the difference is a matter of taste. What an engineer adds is judgement: hearing that the vocal disappears in the second chorus and deciding to do something about it. No automated chain makes that call. If the record matters, a human is still worth the money.
Around -14 LUFS integrated for Spotify, YouTube, Tidal and Amazon; -15 for Deezer; about -16 for Apple Music; -23 LUFS for EBU R128 broadcast. Keep true peak at -1 dBTP or below for streaming, -2 dBTP for video delivery. These are references rather than rules — mastering louder does not make you louder on playback, because the platform turns you back down.
Yes, and it is now one of the most common uses. Tracks from Suno, Udio and Mureka usually need the same things as any other mix: loudness control, tonal balance and true-peak safety. They also tend to share specific traits — crowded low-mids and harsh upper mids — which is why a chain you can adjust usually beats one that applies a fixed result.
Yes. BandLab Mastering and Quantara both deliver clean files with no watermark on their free tiers. Check before you rely on it, though: some services advertise a free master and then place an audible tone or voice-over on the download.
Usually seconds to a few minutes. Services that process in your browser are limited by your own machine; server-based ones by queue length. Either way it is far faster than a traditional turnaround, which is measured in days.