Speed vs. Pitch vs. Tempo
These terms are related but not interchangeable. The audio speed changer controls the time scale directly; the selected pitch mode determines whether pitch follows that change.
| Concept | What it describes | What this tool does |
|---|
| Speed | How quickly the complete recording plays relative to its original timeline. | Sets a 0.50×–2.00× multiplier and changes duration. |
| Pitch | How high or low a sound is perceived. | Preserves it with time stretching, or changes it with varispeed. |
| Tempo | The musical beat rate, often measured in BPM. | Changes overall timing, but does not detect or display BPM. |
| File compression | Encoding choices used to reduce byte size. | Not the main purpose; MP3 export is re-encoded at 192 kbps. |
When to Speed Up Audio
A moderate increase can shorten listening time without making speech difficult to follow. The audio speed changer is especially useful when the source is familiar and the goal is efficient review.
- Review podcasts or lectures at 1.25× or 1.50×.
- Scan meeting and voice recordings for a relevant passage.
- Revisit spoken study material in less time.
- Fit user-created narration to a shorter timing target.
- Check how a recording feels at faster delivery before re-recording.
When to Slow Down Audio
Slower playback gives more time to hear detail. Preserve pitch is usually helpful for comprehension; varispeed is useful only when the accompanying lower pitch is intentional.
- Transcribe a difficult spoken passage.
- Practice listening and pronunciation in a language you are learning.
- Study a performance from audio you created or lawfully possess.
- Review a fast speaker, technical explanation, or unclear recording.
- Examine timing before making a precise cut with the Audio Trimmer.
Common Audio Speed Settings
The examples below start with a ten-minute file. They are mathematical duration results, not file-size guarantees.
| Speed | Approx. new duration | Typical use |
|---|
| 0.50× | 20:00 | Detailed listening or practice |
| 0.75× | 13:20 | Slower speech review |
| 1.00× | 10:00 | Original speed |
| 1.25× | 8:00 | Moderate faster listening |
| 1.50× | 6:40 | Podcasts or lectures |
| 2.00× | 5:00 | Fast review |
How Audio Speed Changes Duration
The calculation is new duration = original duration ÷ speed multiplier. For example, twelve minutes at 1.50× becomes eight minutes because 12 ÷ 1.5 = 8. At 0.75×, the same source becomes sixteen minutes.
Target Duration mode reverses the same relationship: required speed = original duration ÷ target duration. If a target needs less than 0.50× or more than 2.00×, the audio speed changer explains that the request is outside its supported range instead of silently changing the value.
Supported Audio Formats
The local FFmpeg build accepts MP3, WAV, M4A/AAC, OGG, and FLAC inputs after it verifies that a readable audio stream is present. Renaming an unsupported file extension does not convert its codec, and DRM-protected or damaged media may fail inspection.
The audio speed changer always exports a new 192 kbps MP3 and removes source metadata. Source preview playback still depends on the browser’s native audio element; if a browser cannot play the original container, processing may still work and the generated MP3 can be previewed after export.
Privacy and Browser-Based Processing
Inspection, time stretching, varispeed processing, MP3 encoding, and output verification run locally in the browser through the site’s lazy-loaded FFmpeg WASM worker. The audio file, filename, measured metadata, and target duration are not sent to an upload API or attached to analytics events.
The FFmpeg runtime is downloaded when first needed, so an internet connection may be required to load the engine. Large files use device memory and CPU; the shared hard limit is 500 MiB, with earlier warnings on memory-constrained devices. Resetting, replacing the file, or leaving the page revokes temporary URLs and clears worker data.