Time Stretcher: Free Online Tempo Changer for Audio
Change the tempo and speed of any audio file from 25% to 200%. Free online time stretcher for musicians, students, and podcast listeners. Works with MP3, WAV, and more.
Speed up or slow down any audio file with our free Time Stretcher tool. Perfect for practicing music at slower tempos, transcribing fast passages, or consuming podcasts and audiobooks at increased speed.
Time Stretcher
Upload an audio file and change its playback speed (tempo).
Note: Changing tempo also changes pitch. Slowing down lowers the pitch; speeding up raises it. This is the natural behavior of audio playback rate changes.
Supported formats: MP3, WAV, OGG, FLAC, and other browser-compatible audio files.
What Is Time Stretching?
Time stretching changes the duration (tempo/speed) of audio. When you slow down audio, you have more time to hear each note; when you speed it up, you consume content faster.
| Tempo | Speed | Use Case |
|---|---|---|
| 25% | 4x slower | Extreme slow-motion analysis |
| 50% | 2x slower | Learning complex passages |
| 75% | 1.33x slower | Comfortable practice speed |
| 100% | Original | Normal playback |
| 125% | 1.25x faster | Faster content consumption |
| 150% | 1.5x faster | Podcast speed listening |
| 200% | 2x faster | Maximum speed listening |
How to Use This Tool
1. Upload Your Audio
Click Choose Audio File and select any audio file. MP3, WAV, OGG, FLAC, and other browser-compatible formats are supported.
2. Adjust the Tempo
Use the slider or preset buttons to set your desired tempo from 25% to 200%. The tool shows both the original and adjusted duration.
3. Play and Listen
Press Play to hear your tempo-adjusted audio. You can change the tempo in real-time while playing.
Info
Note: This tool uses playback rate adjustment, which also affects pitch. Slowing down lowers the pitch; speeding up raises it. For pitch-preserving time stretching, professional DAW software offers more advanced algorithms.
Common Use Cases
Music Practice
Slowing down music is one of the most effective practice techniques:
- Learn difficult passages: Slow a fast guitar solo to 50% and gradually increase as you improve
- Hear every note: At reduced tempo, you can identify exact fingerings, articulations, and rhythms
- Build muscle memory: Practice at slow tempos to develop accuracy before building speed
Pro Tip: Start at 50% tempo and increase by 5-10% increments. Don't move faster until you can play perfectly at the current tempo.
Music Transcription
When transcribing music by ear:
- Slow down to catch every note in fast runs
- Loop difficult sections
- Identify chord voicings and bass notes more easily
Language Learning
- Slow down native speakers: Reduce tempo to catch pronunciation details
- Podcast comprehension: Slow down content in your target language
- Dictation practice: Slower audio gives you time to write
Content Consumption
Speed up audio to consume more content in less time:
- Podcasts: Many listeners prefer 1.25x to 1.5x speed
- Audiobooks: Speed through familiar sections, slow down for complex parts
- Lectures: Review recorded lectures at increased speed
DJ and Production
- Tempo matching: Adjust track speeds to match your set's BPM
- Beatmatching practice: Slow down to learn transitions
- Sample preparation: Change loop tempos to fit your project
Practice Tips for Musicians
The Slow Practice Method
- Find your starting tempo: Slow the song until you can play it perfectly (often 30-50% of original)
- Master that tempo: Play the section 5 times perfectly in a row
- Increase by small increments: Add 5% tempo
- Repeat until full speed: Continue until you reach 100%
Focus Areas at Slow Tempo
At reduced tempo, pay attention to:
- Timing accuracy: Are you rushing or dragging?
- Dynamics: Are you playing the right loud/soft levels?
- Articulation: Legato, staccato, accents?
- Tone quality: Is your sound clean?
- Fingering efficiency: Are your movements economical?
Understanding the Trade-off
This tool uses the browser's native playback rate adjustment, which is simple but has a trade-off:
| What Changes | Effect |
|---|---|
| Tempo (intended) | Duration changes as expected |
| Pitch (side effect) | Lower at slow speeds, higher at fast speeds |
Why This Happens
Audio is a waveform. When you play it slower, you're literally stretching the wave, which lowers its frequency (pitch). It's like playing a vinyl record at the wrong speed.
The Alternative: Time-Stretch Algorithms
Professional software uses algorithms like:
- Granular synthesis: Cuts audio into tiny grains and rearranges them
- Phase vocoder: Analyzes and resynthesizes the frequency content
- Elastic audio: Real-time, high-quality stretching (Ableton, Pro Tools)
These preserve pitch while changing tempo, but can introduce artifacts and require more processing power.
Frequently Asked Questions
Can I change tempo without changing pitch?
This basic tool does change pitch when you adjust tempo. For pitch-preserving tempo changes, you'll need dedicated software like:
- Audacity (free) – Has time-stretch effects
- Transcribe! – Designed for musicians
- Ableton Live – Professional DAW with Warp
- Amazing Slow Downer – App for musicians
What's the best tempo for practicing?
Start at a tempo where you can play perfectly—often 40-60% of the original. The goal is accuracy first, speed second. If you're making mistakes, you're practicing too fast.
Can I slow down YouTube or Spotify?
Most streaming platforms have built-in speed controls:
- YouTube: Click the gear icon → Playback speed
- Spotify: Not available on desktop, limited on mobile
- Apple Podcasts: Speed controls available
For more control, download the audio and use this tool.
Why does slowed audio sound deep/low?
When you slow down audio, you're stretching the waveform in time. This increases the wavelength of each cycle, which we perceive as lower pitch. It's the same effect as slowing down a vinyl record.
Is there a limit to how much I can slow down?
This tool goes to 25% (4x slower). At extreme slow speeds, audio becomes harder to recognize, and rhythmic patterns stretch beyond what's musically useful. For most practice, 50-75% is the sweet spot.
Can I save the tempo-changed audio?
This tool is for real-time preview. To export, use desktop software:
- Audacity: Free, cross-platform, has time-stretch effects
- FFmpeg: Command-line tool for audio conversion
- Your DAW: Any digital audio workstation can render at changed tempos
Related Tools
- Pitch Shifter – Change the pitch of audio files
- BPM Tap Tempo – Find the tempo of any song
- Metronome – Practice with a steady beat
- Metronome for Guitar – Guitar-specific practice tips
- Interval Training – Train your ear to recognize intervals