How to Change Tempo Without Changing the Pitch
In old recordings, slowing the tape down also dropped the pitch. Modern algorithms decouple the two. Here's how to use that for practice.
Why Tempo and Pitch Used to Be Coupled
If you play a vinyl record at 33 rpm instead of 45, the music slows down AND drops in pitch — about a perfect fifth. That's because vinyl reads waveforms at a constant physical speed; halving the rotation halves both the frequency (pitch) and the playback rate (tempo). Digital audio worked the same way for decades. Early MP3 slow-down tools were really just 'change sample rate,' which coupled speed and pitch like vinyl did. This is fine for novelty (chipmunk voices) but useless for practice — a song in A major dropped to 50% speed is now in D# major, which doesn't help anyone learn the original part.
How Time-Stretching Works
Modern time-stretch algorithms decouple tempo from pitch. They analyze the audio in small overlapping frames, then resynthesize it at a new rate — keeping each frame's spectral content (pitch) but spacing the frames further apart (slower) or closer (faster). The most common approach is the phase vocoder, which uses short-time Fourier transforms. More advanced algorithms (Elastique, Rubber Band, Signalsmith Stretch) add transient preservation, formant correction, and other tricks to reduce artifacts. loope uses Signalsmith Stretch — good quality, fast enough to run in real time in a browser.
Step 1: Load and Set Speed
Drop an MP3, WAV, FLAC, or OGG file onto loope. The Speed slider goes from 0.25× to 2×. For slowing down, 0.75× and 0.5× are the practice sweet spots. 0.25× is extreme but useful for transcribing impossibly fast passages. Above 1×, you can use 1.25× or 1.5× for speeding up podcasts, audiobooks, or practicing a song faster than the recording.
Try tempo change without pitch changeStep 2: Leave the Pitch Slider at Zero
The Pitch slider controls key independently. For pure tempo change, leave it at 0. You'll notice: • The song plays slower • A note that was A 440Hz is still A 440Hz • Chords and melodies are recognizable — nothing sounds detuned • The overall duration scales (a 3-minute song at 0.5× becomes 6 minutes) If you want tempo change AND key change, adjust both sliders independently.
Step 3: Export the Time-Stretched Version
Click Export and pick a format. The saved file plays at the new tempo on any device — phones, speakers, DAWs. You can use it for phone practice (slowed-down audio loaded into a music app) or share it with a teacher. For best quality, export as WAV or FLAC. MP3 re-encoding adds a tiny extra loss, but it's usually invisible for practice use.
Try it now in Loope
Drop a track. Slow it down. Loop the tricky part. Change the key. All in your browser — no upload, no signup.
Open LoopeFrequently Asked Questions
Functionally yes — both preserve pitch while changing speed. loope runs in a browser with no install, while Audacity is a desktop app with more features but a steeper learning curve. For simple tempo changes, loope is faster. For multi-track editing, stay with Audacity.
That's phase vocoder artifact — the algorithm smearing transients. It's most audible on drums and fast percussion. The Signalsmith Stretch engine minimizes this, but it's not zero at extreme slowdowns. Staying between 0.5× and 1× keeps artifacts mostly inaudible.
Not in loope. The speed is a single value applied to the whole track. For tempo automation (speeding up during a bridge, slowing down at the end), a DAW is the right tool.
Yes, but vocals are harder to stretch cleanly than instrumentals — consonants can smear, formants shift slightly. For extreme slowdowns of vocal-heavy tracks, accept some artifacting as a tradeoff for slower playback.
Some — frequencies above ~16kHz can get truncated at high speeds, and transients can blur. Up to 1.5× is usually fine. Above 2× you're better off asking whether you actually need that speed for your use case.