Voxengo SPAN is the most popular free spectrum analyzer plugin — a real-time frequency display you put on any track. MixDiagnose is a free AI mix analysis tool that diagnoses your whole mix and tells you, in plain English, what's wrong and how to fix it. Both free. One shows you a spectrum; the other tells you what to do about it. Here's how they compare.
MixDiagnose and Voxengo SPAN are both free, and they're both about understanding your mix's frequency content — but they answer different questions. SPAN shows you a spectrum. It's a real-time frequency analyzer that displays what's happening in your audio, band by band, as it plays. You look at it and draw your own conclusions. MixDiagnose tells you what's wrong. You upload a mix and it analyzes the whole thing — frequency, loudness, dynamics, stereo, phase, masking — and hands you a report with specific issues, severity grades, and fixes: "Your low end is 6 dB too hot at 60 Hz. Cut 3 dB on your kick and bass." One is a display; the other is a diagnosis. They're both free, so the question isn't cost — it's what you need.
| Feature | MixDiagnose | Voxengo SPAN |
|---|---|---|
| Real-time spectrum analyzer | ✗ | ✓ Best-in-class free analyzer |
| Correlation / phase meter | ✓ Measured and reported | ✓ Real-time goniometer |
| RMS / peak level metering | ✓ | ✓ |
| AI mix analysis | ✓ Automatic issue identification | ✗ |
| Frequency balance vs. genre reference | ✓ dB offsets per band | ✗ Display only — no reference |
| LUFS / loudness measurement | ✓ Integrated, true peak, streaming targets | ✗ RMS and peak only, no LUFS |
| Dynamic range / crest factor | ✓ | ✗ |
| Stereo width per-band | ✓ Measured and reported | ~ Visual via goniometer |
| Phase / mono compatibility check | ✓ Measured and reported | ~ Visual via correlation meter |
| Frequency masking detection | ✓ | ✗ |
| Specific fix recommendations | ✓ "Cut 250 Hz by 3 dB on bass" | ✗ You interpret and decide |
| Severity grading | ✓ Critical / Moderate / Minor / Ideal | ✗ |
| One-click auto-fix | ✓ Corrective EQ on uploaded file | ✗ |
| Runs as a DAW plugin (VST/AU/AAX) | ✗ Web app | ✓ |
| Reference track comparison | ✓ Automatic, genre-matched | ✗ |
| Mid / side / solo analysis modes | ✓ Per-band mid/side reported | ✓ Mid/side routing |
| PDF reports | ✓ | ✗ |
| Batch processing | ✓ | ✗ |
| Platform | Any browser, no install | Windows / macOS DAW |
| Price | Free (3 analyses/mo) · $19/mo Pro | Free |
| Best for | Objective whole-mix diagnosis with specific fixes | Real-time spectrum viewing in your DAW |
Voxengo SPAN is the most-used free spectrum analyzer plugin in the world — and for good reason. It's a real-time FFT spectrum analyzer with configurable block size, overlap, and smoothing. You can view spectrum, spectrogram, or both. It supports mid/side routing, has a correlation meter and goniometer for stereo phase, and shows RMS and peak levels. It's the plugin that lives on almost every engineer's master bus at some point in their career, because it's free, reliable, and does exactly what a spectrum analyzer should do.
If you can read a spectrum, SPAN is a fantastic tool. You see a bump at 300 Hz and know it's mud. You see a dip at 80 Hz and know your low end is thin. You watch the spectrum as you EQ and confirm your cuts are doing what you intend. For real-time, in-DAW frequency monitoring, nothing free beats it — and many paid alternatives don't beat it either.
The limitation: SPAN shows you a spectrum — it doesn't interpret it. It doesn't tell you "your low end is 6 dB too hot relative to a genre reference" because it has no reference. It doesn't measure LUFS, true peak, or dynamic range. It doesn't detect frequency masking or grade issues by severity. It doesn't suggest fixes. If you can read a spectrum and know what "good" looks like for your genre, SPAN is all you need. If you can't — or if you want an objective check that covers more than just frequency — you need a diagnostic tool on top of it.
MixDiagnose analyzes your uploaded mix and tells you, in plain English, what's wrong and where to fix it. You upload one file and in under 30 seconds you get a report covering frequency balance (compared against genre-matched references, with specific dB offsets per band), LUFS and true peak, dynamic range, stereo width per band, mono compatibility, phase, and frequency masking. Each issue is graded Critical, Moderate, Minor, or Ideal — and each comes with a specific fix: "Your low end is 6 dB too hot at 60 Hz. Cut 3 dB on your kick and bass."
It also offers a one-click auto-fix that applies corrective EQ to your upload and gives you a downloadable reference. Because the analysis runs on the file itself, not through your monitors, your room and ears don't affect the result. It's an objective check that works regardless of your monitoring environment — and it covers more than just frequency, all in one report.
The trade-off: MixDiagnose isn't real-time and doesn't run inside your DAW. You upload, wait ~30 seconds, and read a report. You can't watch a spectrum shift as you EQ in real time — that's SPAN's job. MixDiagnose is a diagnostic checkpoint, not a continuous monitor.
SPAN and MixDiagnose are both free, and they're complementary — use both. SPAN is the real-time spectrum display you put on your master bus while you mix. MixDiagnose is the objective diagnosis you run before or after to check the whole picture — frequency, loudness, dynamics, stereo, phase, masking — with specific fixes. There's no reason to choose one over the other when both are free.
The best workflow: run MixDiagnose first to get the objective diagnosis — fix the Critical and Moderate issues it identifies. Then open SPAN in your DAW and watch your spectrum as you apply those fixes, confirming your cuts land where MixDiagnose said they should. MixDiagnose tells you where to cut; SPAN confirms you cut it. SPAN has no reference, no LUFS, no dynamics — MixDiagnose covers all of that in one report.
If you can only pick one: choose SPAN if you can read a spectrum and want real-time frequency monitoring during your session. Choose MixDiagnose if you want an objective AI diagnosis of your whole mix — with genre-matched references, specific dB offsets, severity grades, and fixes across loudness, dynamics, stereo, and phase. Both free — so ideally, use both.
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