Turn any short recording into a seamless, endless loop, or stretch it into a long evolving texture — for live theatrical sound design, ambient beds, or anywhere you need audio that plays forever without a click at the seam. FermaLoop is a portmanteau which blends fermata — the musical notation for a held note or pause, sustained for as long the performer chooses — with loop, reflecting the app’s purpose: turning a short audio clip into a seamless, indefinitely extendable loop that a live operator can hold or release on cue, much like a fermata itself.
- Load a file — drag it onto the window, or click Browse.
- Select the region you want to loop by dragging on the waveform.
- Click LOOP (crossfaded) or REPEAT (declicked) to preview it.
- Adjust crossfade settings if needed — the preview updates live.
- Click Save — it exports exactly what's currently armed (LOOP or REPEAT), using your current selection. Cropping first is optional.
- Drag and drop a file anywhere onto the window.
- Or click Browse next to Input and pick a file.
- Supported formats: WAV, AIFF, MP3, MP4/M4A, FLAC.
- Click and drag on the waveform to make a selection.
- Drag the white edge bars at the selection boundaries to adjust it.
- Click anywhere in the waveform to move the playhead there.
- Hover over the waveform (without clicking) to see the time at the cursor position, shown as a small flag above the ruler.
- Scroll wheel zooms in/out, centered on the cursor. Hold Shift while scrolling to pan instead.
- The small ✕ in the top-right corner of the waveform unloads the current file.
These six icons are the actual buttons in the transport row — everything else (Rewind, Zoom, Undo/Redo) is keyboard-only; see Keyboard Shortcuts below. Deliberately using plain text here rather than guessed icon glyphs — get the real icon crops from a screenshot instead of a placeholder attempting to reproduce them.
| BUTTON | ACTION |
|---|---|
| Play / Pause | Start or pause playback |
| Stop | Stop playback |
| REPEAT | Loop the raw selection with declicked edges |
| LOOP | Loop the selection with a crossfaded seam |
| Crop | Trim the loaded file down to the current selection |
| Stretch | Open PaulXStretch (extreme time-stretch) |
LOOP vs. REPEAT — which one do I want?
- REPEAT: plays the raw selection over and over, with just enough fade at the wrap point to prevent a click. Fast, no processing, but the seam is still audibly “the end of a clip going back to the start.”
- LOOP: blends the tail of the selection into its head over an adjustable crossfade, so the wrap point is inaudible — the loop sounds continuous. This is what actually gets processed into the saved file.
Only one of the two can be active at a time — enabling one turns the other off. Space starts/pauses whichever is armed; pressing REPEAT or LOOP again while something is already playing switches to it live, without stopping playback. Stop is the only thing that actually stops audio.
- XFADE CURVE — Equal power (smoother, constant perceived loudness) or Linear (simpler, can dip slightly in the middle).
- XFADE OVERLAP — Manual (type an exact crossfade length in seconds) or Auto (analyzes the selection and picks a length that minimizes an audible seam).
- LOOP ALIGNMENT — Snap to transients, with an adjustable search window, trims the selection to start/end right on the nearest strong attack instead of an arbitrary sample boundary.
All three update the LOOP preview live while it’s playing — no need to stop and re-audition after changing a setting.
Stretches the current selection into a long, evolving, textural bed — based on the “Paul’s Extreme Sound Stretch” technique. Best suited to ambient/drone material; rhythmic content will smear into texture, which is inherent to how the technique works, not a bug.
- Open it from the Stretch button, set the two values below, apply.
- The result replaces the current selection and can be undone (Cmd/Ctrl+Z) like any other edit.
- Re-audition (LOOP/REPEAT) or Crop afterward to continue building the loop from the stretched result.
Stretch factor — how much longer the output gets. Typical range 2–50; higher takes longer to compute and produces proportionally longer output.
Window size — the analysis window length, in seconds, the stretch algorithm processes at a time. Typical range 0.05–2.0s; 0.1–0.25s is a good starting point.
- Smaller windows reduce amplitude pulsing but can sound grainier or less full.
- Larger windows sound fuller but may pulse more.
- This is a genuine per-track trade-off, not a setting with one correct value — try both ends of the range on your material before settling on one.
FermaLoop’s stretch feature is a from-scratch reimplementation of the core algorithm behind Paul’s Extreme Sound Stretch, created by Nasca Octavian Paul — the original tool lives at hypermammut.sourceforge.net/paulstretch. The name “PaulXStretch” specifically nods to Xenakios's modern continuation of the project, PaulXStretch (source), which FermaLoop’s own feature is named after. No code is shared between the two — FermaLoop’s implementation is its own — but the technique and its name both originate there, and crediting that clearly here felt like the right thing to do.
Cropping trims the loaded file down to just the current selection. You don't need to crop before saving — Save always processes and exports only the current selection regardless of whether you’ve cropped. Crop is useful if you want to keep working with just that trimmed region (e.g., before a further Stretch), or want the loaded file itself to match the final loop length.
- Set Format — FLAC (lossless), MP4 (Apple Lossless), or MP3 (VBR). These are the only three export formats; input can be loaded from a wider set (WAV, AIFF, MP3, MP4/M4A, FLAC), but saving is limited to these three.
- Confirm or change the Save As path — it auto-fills next to the
input file, with a suffix (
LOOP,REPEAT, orRAW) that tracks whichever mode is currently armed. - Click Save — the button label itself always reflects what will actually happen: Save Crossfaded, Save Declicked, or Save Unprocessed.
Cmd/Ctrl+Z / Shift+Cmd/Ctrl+Z — covers selection changes, Crop, and PaulXStretch.
Every shortcut below is remappable — click the ⚙ icon (top right) to open Preferences and Help, then click any shortcut’s key and press a new one to reassign it.
| Action | Default key |
|---|---|
| Play / Pause | Space |
| Stop | S |
| Rewind | Home |
| REPEAT (declicked edges preview) | R |
| LOOP (crossfaded edges preview) | L |
| Crop to Selection | C |
| Undo / Redo | Cmd/Ctrl+Z / Shift+Cmd/Ctrl+Z |
| Zoom In / Out | + / − |
| Zoom to Fit | 0 |
| Zoom to Selection | 9 |
| Stretch (open PaulXStretch) | X |
- No sound / playback controls greyed out: the optional
sounddevicepackage isn't installed — file processing and export still work without it. - Drag-and-drop doesn’t work: the optional
tkinterdnd2package isn’t installed — use Browse instead. - A Finder window briefly flashes on first launch or first file load (macOS only): this is normal, one-time macOS behavior tied to drag-and-drop and file-dialog initialization, not an app problem. It doesn’t recur on later launches.
MIT — free to use, modify, fork, and distribute, including
commercially, with attribution. See LICENSE for the full
text.
For build/technical details — architecture, dependencies, and the build process — see DEVELOPMENT.md.