Audio Editor (Multi-Track: Cut, Fade, Mix Voice with Music)
Cut, fade and mix several recordings on a timeline — on your device, no upload.
Click the ruler to place the playhead, drag along it to select time. Drag clips to move them, their edges to trim, the squares at their top corners to fade. Keys on the timeline: Space plays, S splits, Delete deletes, Ctrl+C / X / V copy, cut and paste, Ctrl+D duplicates, Ctrl+Z undoes, arrows move the playhead (Shift: 1 s), + and − zoom.
About the Audio Editor (Multi-Track: Cut, Fade, Mix Voice with Music)
A waveform audio editor with several tracks, in your browser: put a voice recording, background music and sound effects on their own tracks, then cut, split, move, trim, fade and set the volume of each clip, change its speed (keeping the pitch) or its pitch (keeping the speed), and let the music duck automatically whenever someone speaks. Play the mix as you go and export it as MP3, M4A (AAC) or WAV, normalised to a loudness target if you like.
Files are decoded and mixed on your device with Web Audio — nothing is uploaded. Undo and redo cover every edit, and the inspector beside the timeline does everything by keyboard as well as by mouse or touch.
How to use it
- Choose your audio files (or videos, to use their sound). Each file becomes its own track; tracks with “music”, “song” or “bgm” in the name are marked Music, the rest Voice — change it in the Track tab.
- Arrange the clips: drag them along a track or onto another, drag their edges to trim, the small squares at their top corners to fade, and press S (or Split) to cut at the playhead. Select a time by dragging along the ruler; Delete removes the clip or that time from every track.
- In Clip, set the volume, fades, Normalise, or Apply speed and pitch. In Mix, turn on Turn the music down while someone speaks and adjust how much and how fast.
- In Export, pick MP3, M4A or WAV, the quality and the level, then Export the mix. Listen to the result and download it.
Examples
host.wav on a Voice track · intro-music.mp3 on a Music track · ducking on, 12 dB
The music plays at full level, drops 12 dB a quarter of a second before the host starts talking, stays down while they speak and comes back up in the pauses — exported as a 192 kbps MP3 at −16 LUFS
interview.m4a · select a cough on the ruler · Delete
The cough is cut out of every track and everything after it moves up to close the gap
song.mp3 · Speed 0.75× · Pitch 0 · Apply
The same song at three-quarters speed in the same key, ready to export as WAV for practice
Tracks, clips and editing
A clip plays a part of a file on one track; clips on a track never overlap, so a clip you drop on another one moves to the nearest free place. Trimming never goes past the start or end of the recording, and edges snap to other clips, the playhead and the start (turn Snap off to place them freely). Split cuts the clip under the playhead in two; Delete this time (in Mix, or Delete with a time selected) removes a stretch from every track at once and closes the gap — the quickest way to take out a mistake. Copy, cut, paste and duplicate work on the selected clip, and every change can be undone.
Each track has a volume, a pan position, Mute (M) and Solo (S). The waveform on each clip shows its volume and fades, so you see what you will hear.
Ducking music under a voice
Mark the speech tracks Voice and the background tracks Music, then turn ducking on in Mix. The editor measures the voice tracks’ short-term level every 10 milliseconds; while it is above the threshold, the music goes down by the amount you set (12 dB by default), starting a little early so the first word is clear, staying down for a short hold, and coming back up over the release time. The preview and the export use the same envelope.
Speed, pitch and normalising
Speed changes how fast a clip plays without changing its pitch, and Pitch moves it up or down in semitones without changing its speed — with the Signalsmith Stretch library on your device. It makes a new version of the clip’s sound (later clips on the track move out of the way when it gets longer), and Undo goes back to the original.
Normalise sets a clip’s volume so that its loudest sample sits at −1 dBFS, or so that its integrated loudness (ITU-R BS.1770) reaches −16 or −14 LUFS without its loudest sample going over −1 dBFS.
Export levels
The export can keep the mix as it is (only turned down if it would clip), set its loudest sample to −1 dBFS, or bring its integrated loudness to a target: −16 LUFS is the level Apple Podcasts asks for, with peaks no higher than −1 dBFS (Apple Podcasts audio requirements); −14 LUFS is the level Spotify plays music at (Spotify loudness normalization); −23 LUFS is the EBU R 128 level for broadcast (EBU R 128). The mix is measured first and then encoded, so the level is exact; when a loudness target would push peaks over −1 dBFS, the export stops short of it and says so.
Limitations
- Files are decoded into memory: the editor holds up to 120 channel-minutes of audio (an hour of stereo, two hours of mono). Long recordings on a phone may need to be cut first.
- Peaks are measured on the samples (sample peak); the true peak some platforms measure can be a little higher after lossy encoding.
- Speed and pitch need AudioWorklet (current Chrome, Edge, Firefox and Safari) and work on one clip at a time; very large changes (0.5× or 2×, ±12 semitones) sound more processed.
- There is no recording, noise removal or effects rack here; record with the Voice Recorder and come back with the file.
- The project is not saved: it lives in this tab until you close it, so export before you leave.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
Can I add background music to a voice recording?
Yes. Add both files: the voice and the music each get a track. Mark the music track Music, turn on ducking in Mix, and the music will dip under the voice by itself. Then export.
How do I cut out a part in the middle?
Drag along the ruler over the part to select it, then press Delete (or Delete this time in Mix). It is removed from every track and the rest moves up. To cut just one clip, put the playhead on it and press S to split, then delete the piece.
Does changing the speed change the pitch?
No: Speed keeps the pitch, and Pitch keeps the speed. Use both together to change each separately.
Which format should I export?
MP3 plays everywhere; M4A (AAC) sounds better at the same size and is what Apple recommends for podcast feeds; WAV is uncompressed, for further editing. 44.1 kHz suits music and podcasts, 48 kHz video.
Are my recordings uploaded?
No. Files are read, mixed and encoded inside your browser; nothing leaves your device.