Audio Trimmer & Converter – Manual

User Manual

Overview

Audio Trimmer & Converter runs entirely in your browser using the Web Audio API — no server, no upload, no account. Drop in an audio file, drag the green and red trim handles to select the region you want, preview it with speed and volume controls, optionally apply normalization or karaoke mode, then export the trimmed clip in the format of your choice. Your audio never leaves your device.

Getting Started

Loading an audio file

Drag & drop — drag any audio file from your file manager onto the drop zone in the centre of the screen.
Browse — click the Open Audio File button (or anywhere on the drop zone) to open a file picker.

The app decodes whatever format your browser supports, which typically includes MP3, WAV, OGG, M4A, FLAC, AAC, and WebM.

Exporting / saving

Select your trim region, choose any effects, then click one of the export buttons (WAV, WebM, OGG, MP3) in the Export panel.
The downloaded file is named automatically: originalname_trim_START-END.ext.
WAV is always available. MP3 requires the lamejs CDN library to load. OGG and WebM depend on browser support (Chrome/Edge support WebM; Firefox supports OGG).

The Waveform

After loading a file, the waveform is drawn on a canvas showing peak amplitude for the entire file. The coloured handles let you define the trim region:

Green handle — trim start point. Drag it right to cut the beginning.
Red handle — trim end point. Drag it left to cut the end.
Click inside the trimmed region — sets the playhead to that position.
The dimmed areas outside the handles are the parts that will be discarded on export.
The dashed yellow line is the live playhead during playback.

Tip: Handles have a 12 px grab zone. If you miss, zoom your browser in or try clicking slightly closer to the coloured line.

Transport Controls

Control	What it does
▶ Play / ⏸ Pause	Starts or pauses playback from the current playhead position within the trim region.
⏹ Stop	Stops playback and resets the playhead to the trim start.
Speed slider	Changes playback rate from 0.25× (slow motion) to 2× (double speed). Restarts playback immediately when adjusted.
Volume slider	Scales output volume from 0% to 200%. Applies in real time during playback.
Playhead time	Shows the current position in the file as `M:SS.s`.
Trim display	Shows the selected trim window as start → end with duration. Says "full file" when no trim is applied.
Reset trim	Restores trim handles to cover the full file.

Effects Panel

Peak Normalize

Click Peak normalize to scan the full file for the loudest sample and calculate a gain multiplier that brings that peak to 0 dBFS (full scale). The calculated gain is shown next to Gain applied. This gain is applied during both preview and export — the source file is not modified.

Note: Normalize scans the entire source file, not just the trim region. If you only want to normalize the trimmed clip, export it first, then re-load it.

Karaoke Mode

Karaoke mode uses a phase-cancellation technique: it subtracts the average of the left and right channels from each channel, which removes audio that is panned to the exact centre — typically lead vocals in a stereo studio mix.

Requires a stereo file (mono files show an error).
Works best on commercially produced music where vocals are centre-panned.
Will also remove any other centre-panned element (kick drum, bass).
Does not use AI — it is a simple mathematical operation, so results vary greatly by recording.

How to use: Load a stereo track, click Off to toggle karaoke on (button shows On ✓), then press Play to preview. Export as usual; karaoke is baked into the exported file.

Export Panel

Format	Notes
`WAV`	Uncompressed PCM, 16-bit. Always works, largest file size. Best for further editing.
`MP3`	128 kbps, encoded via lamejs (loaded from CDN). Requires an internet connection on first use. Not available if lamejs fails to load.
`WebM`	Compressed via MediaRecorder. Supported in Chrome, Edge, and most Chromium browsers. Not available in Safari.
`OGG`	Compressed via MediaRecorder with Ogg Vorbis mux. Best supported in Firefox. May not be available in Chrome/Edge.

Tip: If an export format button fails with an error in the status bar, fall back to WAV — it always works and can be converted elsewhere.

Keyboard Shortcuts

Shortcut	Action
`Space`	Play / Pause
`Escape`	Stop playback and reset playhead
`Ctrl+N`	Apply peak normalization

Privacy

Audio Trimmer & Converter processes everything locally in your browser using the Web Audio API. No audio data, metadata, or filenames are transmitted to any server. The app does not use localStorage — nothing is stored between sessions. The only external network request is loading the lamejs library from the Cloudflare CDN when you first use MP3 export.

Supported Input Formats

Any format your browser can decode. Common formats include:

.mp3 · .wav · .ogg · .m4a · .aac · .flac · .webm · .opus

Note: FLAC and OPUS support varies by browser. If a file fails to decode, try converting it to WAV or MP3 first.

About this tool

Technologies used:

Built with:

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