Charlie Crown presents
MASTERPROOF
Is your master
actually ready?
Drop your final master. In 30 seconds, 11 checks tell you if it's ready for streaming — and exactly what to fix if it's not.
Drop your master here
WAV, AIFF or FLAC · or click to choose
Free verdict · full report unlocks with your email · never uploaded
Built by Charlie Crown — 50M+ streams, major-label releases.
The errors you can't hear
It sounds perfect on your monitors. That's the trap.
You bounce the final, it hits hard in the studio, you hit upload. Then the platform, the encode, or the club rig quietly wrecks it — and by the time you find out, it's public, streaming, and permanent.
Spotify turns your loudness down
All that limiting to stay competitive? Undone at their gain knob. You kept the squash and threw away the transients for nothing.
Your peaks clip on encode
Your samples read under 0 dBFS in the DAW, but the wave between them clips the second it becomes an MP3 or AAC. Distortion you never heard while mixing.
Your bass vanishes in mono
Club subs sum to mono and phones are mono. If your low end is out of phase, it cancels — right where the drop is supposed to hit hardest.
Distributors reject it silently
Wrong sample rate, a 32-bit float file, a fade chopped mid-tail — rejected or quietly degraded before a single person hears it.
What you get back
A verdict you can screenshot — and the exact fix for what's off
No raw numbers without an answer. Every issue comes with one plain-English sentence telling you how to fix it.
Sample report
Your true peak is +0.3 dBTP — just over full scale. This is common on loud modern masters and usually inaudible, but lossy encoders (Spotify/Apple) can push it a little further and add distortion. Plenty of loud-genre engineers accept this trade-off on purpose — it's a risk to weigh, not a mistake.
Fix: Your call: keep it if it sounds the way you want, or if you'd rather carry zero encode risk, a true-peak ceiling in the -1.0 to -0.1 dBTP range removes it.
You mastered to -6.5 LUFS integrated — a loud, competitive master, right where modern club, EDM, hip-hop and reggaeton records live. Your loudest 3 seconds hit -4.2 LUFS (around 1:24) — that's how hard your peak sections land. Spotify plays everything at -14 LUFS, so it turns this down about 7.5 dB on playback (see the per-platform table below). The trade-off: extra loudness buys impact and density anywhere it isn't normalized (clubs, DJ sets), at the cost of dynamic range — on normalized streaming it lands at the same perceived level as a quieter master. If it sounds the way you intend, that's the right call.
Your low end below 120 Hz loses +4.0 dB when the track folds to mono — the sub is partly cancelling out of phase. Club systems sum the subwoofer to mono and phone speakers are mono, so your bass disappears exactly where it's supposed to hit hardest.
Fix: Mono your low end below the crossover — a utility/imager set to mono under ~120 Hz, or check that no bass layer has a flipped polarity or heavy stereo widening.
How it works
Thirty seconds, start to verdict
Drop your master
WAV, AIFF, or FLAC — straight from your bounce.
It analyzes in your browser
Nothing is uploaded. Real BS.1770-4 metering, about 30 seconds.
Get a PASS/FAIL verdict
Every issue in plain English, with the exact fix. You stay in control.
What it checks
Every release-killer, in one pass
Loudness vs. every platform
Exactly how far Spotify, Apple, YouTube and TIDAL will turn you down.
True peak
4× oversampled (BS.1770-4) — catches the intersample clipping that ruins lossy encodes.
Mono compatibility
Whether your low end survives club PA and phone speakers.
Format validity
Sample rate, bit depth, container — before a distributor rejects it.
Silent killers
DC offset, chopped fades, dead air at the head — the ones nobody catches.
The math
One bad release costs more than a lifetime of checks
A rejected upload costs you a launch date you can't get back. A mastering engineer charges $50–150 a track to catch this. A public release with clipped peaks is permanent.
Masterproof is free for your first check every month. Five more that never expire? $9. Checking your master should be the cheapest, easiest thing you do before you hit distribute — so it is.
Who built this
I'm Charlie Crown.
Miami-based producer with 50M+ streams and releases on Universal, Sony Music, Ultra, and Dim Mak. I've mastered records that charted — and still caught myself about to upload a master with a clipped peak I couldn't hear.
So I built the tool I wish I'd had: the 30-second check before you hit distribute. No guessing, no plugin to learn — just the truth about your master. Unlock a report and you'll hear from me now and then with producer tips. That's the whole deal.
Why trust the verdict
Measured, not guessed
It won't judge your mix or master it for you — those are your call. It catches the technical mistakes your ears can't, and shows its work.
Built by a charting producer
50M+ streams, with releases on Universal, Sony Music, Ultra, and Dim Mak — not a plugin company guessing at what producers need.
Matches the meters engineers trust
Loudness and true peak agree with Youlean and iZotope Ozone within ±0.1. Same standard (BS.1770-4), same numbers.
Your audio never leaves your device
Analyzed in your browser and discarded when you close the tab. No upload, no storage — ever. Safe for unreleased music and client work.
Pricing
Start free. Pay only if you check constantly.
Free
For the occasional final check.
No card required
Credits
For the producer shipping a few releases.
One payment · yours forever
Unlimited
Best valueFor engineers and prolific producers.
≈ $6.58/mo · save 45% vs monthly
Cancel anytime · self-serve billing
Secure checkout by Stripe. Your card details never touch our servers. No refunds on credits or completed checks; subscriptions cancel anytime.
Questions
The honest answers
Is my audio really private?
Yes. The analysis runs entirely in your browser with WebAssembly — your file is never uploaded, transmitted, or stored, and it's discarded when you close the tab. Our servers only ever receive the resulting numbers.
Can I use it on unreleased tracks and client work?
That's exactly what it's built for. Because nothing leaves your device, there's no risk in checking a track nobody's heard yet.
How accurate is it?
Loudness (LUFS-I) and true peak match Youlean Loudness Meter and iZotope Ozone within ±0.1 — the same references mastering engineers rely on. It's the BS.1770-4 standard, not an approximation.
Will it master my track for me?
No, and that's the point. It tells you exactly what's technically wrong and how to fix it. The creative decisions stay yours.
What files can I check?
WAV, AIFF, and FLAC. Drop in an MP3 or AAC and it'll warn you — you shouldn't distribute a lossy file in the first place.
What if I don't understand the numbers?
You don't have to. Every result is a plain-English verdict with one sentence telling you the fix. No jargon without a translation.
Is it actually free?
Yes — one full check every month, no credit card. You only pay if you check masters often enough to want more.
Stop guessing before you hit distribute
Thirty seconds now beats a permanent mistake later. Free to start, and your audio never leaves your device.
Check my master — free