Settings for this task
| Use case | Setting | What to check |
|---|---|---|
| Language practice | 0.75× | Preserve a natural rhythm where possible. |
| Lecture review | 1.25× or 1.5× | Check technical terms remain understandable. |
| Difficult passage | 0.5× | Expect longer duration and possible texture changes. |
How to use this tool
- Upload the recording and choose a speed preset.
- Check that the estimated listening duration suits your purpose.
- Download and listen for intelligibility, rhythmic clarity and time-stretch artifacts.
Calculated size examples
Calculated, not measured uploads: bytes ≈ bitrate (kb/s) × seconds × 1,000 ÷ 8. MB here means 1,000,000 bytes. Headers, tags and variable bitrate affect actual size. Channels are already included in the total bitrate; do not multiply again.
| Output duration | Format | Bitrate | Estimated audio payload |
|---|---|---|---|
| 20:00 | MP3 | 192 kb/s | 28.8 MB |
| 10:00 | MP3 | 192 kb/s | 14.4 MB |
Calculate the new duration
Output duration is approximately input duration divided by the speed factor. A ten-minute source becomes twenty minutes at 0.5×, eight minutes at 1.25× and five minutes at 2×. At the same output bitrate, a slower version also needs more encoded bytes. Speeding up is not the same as trimming content.
Pitch preservation has limits
Time stretching rearranges the timing of audio without intentionally shifting notes or voices. Sustained instruments, fast percussion and reverberation may sound different after large changes. This is not a pitch-shifter or key-transposition tool. If precise practice tone matters, compare moderate settings before committing to a large slowdown.
Choose a file export or player control
If you only want to listen faster once, your player's speed setting may avoid another encoded copy. Exporting here is useful when the receiving app cannot change speed or you need a fixed-duration practice file. The original remains important because returning an altered MP3 to 1× will not undo all processing artifacts.
Questions about this operation
- Does 2× change the speaker's pitch?
- The processor aims to preserve pitch using time stretching. Timbre can still change, especially at extreme settings.
- Why did slowing down increase file size?
- More output seconds require more bits at the same encoding bitrate. The size change follows duration.
- Does the 1× preset leave the file untouched?
- No, this processing path still encodes output. Keep the original if no speed change is needed.
- Can I change speed midway through a track?
- One speed applies to the whole uploaded recording. Prepare separate excerpts for different speeds.
- Can this change the musical key?
- No key or semitone control is provided. Use a pitch-transposition tool for that separate task.