Phantom

Phantom is a free audio analysis toolkit with 17 tools for mixing and mastering. Point it at your stems and it measures spectral balance, EBU R128 loudness, dynamics, phase coherence, stereo imaging, and frequency masking between instruments. It also scans for nine categories of problems, from clipping and DC offset down to sibilance, mud, and resonances.

You'd typically run Phantom before you start mixing.

Is that low-end buildup a 60 Hz hum or just the bass guitar?

Are the vocals and guitars masking each other at 3 kHz?

Instead of hunting through a spectrum analyzer, you get the answers as numbers with severity ratings.

Phantom works through MCP (Model Context Protocol), which means it plugs into AI assistants like Claude, Cursor, or Windsurf. You describe what you want to analyze in plain English, and Phantom runs the measurements. It can also apply fixes directly in REAPER: EQ corrections, de-essing, sidechain routing, parallel compression. No knob-hunting required.

Stem separation is built in via Demucs (vocals, drums, bass, other). You can batch-analyze up to 50 files at once, A/B against a reference track, or check your mix against one of nine genre profiles.

Runs locally on your machine. Nothing gets uploaded. AGPL-3.0 licensed, always free for personal use. Commercial licensing available for studios and products that need it.