chapterpass
Audible's ACX has eight technical checkpoints, and a file that misses one comes straight back. chapterpass masters each chapter file to spec: RMS loudness between -23 and -18 dBFS, peaks held below -3 dBFS, a noise floor under -60 dBFS RMS, room tone at the head and tail, and a 192 kbps CBR MP3 on the way out. Every output is verified against the full spec before download, and you see the measured value next to the requirement for each checkpoint. The processing runs in your browser through WebAssembly, so your audio never leaves your device. There is no account to create. Your first file is free, then $36 per finished hour, $27 from 5 hours, $18 from 10 hours, billed by the second. A free measurement page at /free-acx-check reads your loudness, peak, noise floor and silence padding against the spec without mastering anything. chapterpass masters the measurable technical specs. It does not edit your recording, remove noise, or fix narration.
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Euphona
Euphona is a browser-based AI audio production platform. Upload a mix, stems or a raw recording and it is analysed once (loudness and dynamics over time, spectral balance, key and tempo, transients and damage). Six capabilities work from that shared analysis: AI mastering with a measured loudness report and a -1.0 dBTP true-peak ceiling by default; stem separation into up to six stems; audio restoration for hum, clicks, noise, clipping and room; vocal tuning; mixing from your own stems; and binaural spatial audio for headphones. Every result is played back level-matched against the original. A developer API runs the same engine, with free test-mode keys. Free no-account browser tools include a loudness checker, BPM and key finder, spectrum analyser, stereo width analyser, clipping detector and vocal remover. Uploaded audio is never used to train models. Plans start free with 10 minutes of processing; paid plans are $15, $29 and $79 per month.
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Automix
RoEx Automix is a web-based and desktop audio production tool for musicians, artists and producers. It analyzes multitrack stems and creates a mix by setting levels, panning, equalization, compression and effects, then can master the result or master a finished stereo track. Users can preview mixes, adjust stem importance and levels, and use Mix Console controls for further changes. Automix supports up to 16 tracks on the free plan and up to 32 with Pro. It can export processed audio and editable project files for compatible digital audio workstations, including Ableton Live, Bitwig Studio and Fender Studio. Desktop editions for macOS and Windows process mixing and mastering locally; the browser version runs as a cloud service. Free previews are available, with paid download credits and subscription plans for additional downloads and features.
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Moozix
Moozix is an AI stem mixing and mastering platform for musicians who want to hear their song finished without building a mix from scratch. Upload stems, a rough mix, or one full audio file, and Moozix creates a private mix and master preview so you can hear the transformation before exporting final files.
Moozix is built for artists, producers, and home studio creators working with vocals, drums, bass, guitars, beats, instruments, or AI-generated music. It can help balance levels, shape EQ, control dynamics, improve stereo width, manage loudness, and move the track toward a more polished release-ready sound.
Unlike mastering-only tools, Moozix is designed for songs that may still need mixing decisions before the final master. Users can work from multitrack stems when they have them, or start from a full song file when they need a simpler path. Pro exports can include a 24-bit WAV master, MP3 preview, premaster mix, and processed stems for continued work in a DAW.
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