⏱️ Free Online Audio Speed Changer
Slow down MP3s, speed up audio, or change tempo — without changing pitch
Ready to change speed? Use our free tool now:
Open Speed Changer Tool →🔬 The Science: How Time Stretching Works
Changing speed without changing pitch requires sophisticated algorithms. Here's what's happening under the hood:
The Challenge
Normally, speed and pitch are locked together. Play a tape faster → higher pitch (chipmunk voice). Play it slower → lower pitch (monster voice). The goal of time-scale modification (TSM) is to break this link.
The Solution: Overlap-Add Methods
Modern time stretchers use overlap-add techniques. The most common are:
- •SOLA (Synchronized Overlap-Add) — chops audio into overlapping segments and crossfades them at optimal points
- •WSOLA (Waveform Similarity OLA) — improved version that finds the best matching waveforms to minimize artifacts
- •Phase Vocoder — works in the frequency domain using FFT, better for polyphonic music
WSOLA: Slowing Down Audio
💡 Why Quality Varies Between Tools
The difference between good and bad time stretchers comes down to:
- •Segment matching — finding optimal crossfade points to avoid clicks and pops
- •Transient detection — drums and attacks need special handling to stay crisp
- •Extreme ratios — below 0.5× or above 2× gets exponentially harder
📜 A Brief History of Time Stretching
The ability to change tempo without affecting pitch has evolved dramatically over the decades:
1940s–1970s: Mechanical Solutions
Early attempts used rotating head tape machines and variable-speed film projectors. The Springer Tempo Changer (1950s) and Lexicon Varispeech (1970s) were pioneering hardware units, but quality was limited.
1978: SOLA is Born
Rabiner and Schafer published foundational work on time-domain methods. The Synchronized Overlap-Add (SOLA) technique used pitch detection and crossfading — faster than phase vocoders but struggled with complex harmonics.
1993: WSOLA Breakthrough
Verhelst and Roelands at Vrije Universiteit Brussels introduced WSOLA — a smarter version that finds optimal waveform matches. This became the foundation for most modern real-time time stretchers.
2000s: DAW Integration
Ableton Live (2001) made time stretching mainstream with its revolutionary warping engine. Pro Tools, Logic, and other DAWs followed with their own algorithms. Suddenly, DJs and producers could remix at any tempo.
Today: Browser-Based & AI
Web Audio API enables real-time time stretching in browsers — no plugins needed. AI-powered tools are emerging that can intelligently separate and process different elements (drums, vocals, bass) independently.
🐢 Slow Down MP3 Files Online
Need to slow down an MP3 to catch every note or word? Our tool lets you reduce playback speed from 0.5x to 1.0x while keeping the original pitch intact — no chipmunk or monster voices.
Why Slow Down Audio?
Slow to 0.5x, nail each note, gradually increase speed.
Catch every word in fast rap or accented speech.
Native speakers too fast? Slow down to understand.
Learn complex moves step-by-step at reduced tempo.
Pro tip: Start at 0.75x for moderate slowdown, or 0.5x for detailed study. Gradually increase speed as you master the material.
🚀 Speed Up MP3 & Audio Files
Want to speed up MP3s or other audio files? Increase playback from 1.0x up to 1.5x while maintaining the original pitch — perfect for consuming content faster or increasing workout intensity.
Why Speed Up Audio?
1.25x-1.5x saves hours on educational content.
Finish books faster without losing comprehension.
Get through your backlog efficiently.
Increase BPM for higher-energy exercise.
🥁 Change Tempo & BPM of Songs
Our tempo changer lets you adjust the BPM (beats per minute) of any song without affecting pitch. This is essential for DJs, music producers, and anyone who needs precise tempo control.
Understanding Speed vs BPM
Speed multiplier directly affects BPM:
- •Original 120 BPM × 0.75x = 90 BPM (slower)
- •Original 120 BPM × 1.25x = 150 BPM (faster)
- •Original 120 BPM × 1.5x = 180 BPM (much faster)
Common Tempo Change Use Cases
❓ Speed Changer FAQ
Does pitch change when I change speed?
No! Our tool uses time-stretching technology to keep pitch constant. You can slow down or speed up audio while maintaining the original key and tone. Want to change pitch? Use our Pitch Changer instead.
What's the best speed for learning music?
Start at 0.75x for moderate difficulty passages, or 0.5x for complex, fast sections. Gradually increase by 0.05x as you master each tempo until you reach full speed.
Can I change both speed AND pitch?
Yes! Our tool lets you adjust speed and pitch independently. Slow down a song AND transpose it to a different key — perfect for learning songs at your own pace and in your comfortable vocal range.
What formats work with the speed changer?
We support MP3, WAV, FLAC, M4A, AAC, and OGG — all processed directly in your browser. Files up to 250MB are supported. WAV and FLAC give the cleanest results for extreme tempo changes.
🎯 When to Use Speed Control
Slow Down For:
Recommended: 0.75× for moderate, 0.5× for detailed study
Speed Up For:
Recommended: 1.25× for comfort, 1.5× for efficiency
🔄 Need to Change Pitch Instead?
Speed changes the tempo (how fast it plays). Pitch changes the key (how high or low it sounds). They're independent! Check out our Audio Pitch Changer or read Pitch vs Speed explained.
Ready to Change Speed?
Slow down or speed up any audio — free, fast, and private.
Open PitchChanger.io →