About

Accuracy in timing is the difference between an amateur and a professional. This Tempo Changer utilizes the Web Audio API's advanced Time Stretching algorithms to decouple playback speed from pitch. Unlike traditional analog tape, where slowing down audio lowers the pitch (the Doppler Effect), digital signal processing allows us to maintain the original key while altering the duration.

Formulas

Time Dilation Formula:

The new duration is inversely proportional to the playback rate:

t′t = 1r

Where r is the playback rate factor (e.g., 0.5 for half speed, 2.0 for double speed).

Pitch Preservation:

Normally, frequency f shifts with rate. To maintain f while changing r, we apply Granular Synthesis or Phase Vocoding techniques natively within the browser engine.

Reference Data

Tempo Marking	BPM Range	Effect at 0.5x (Slow)	Effect at 0.75x (Practice)	Effect at 1.25x (Speed)
Grave	25 - 45	Glacial (~12-22 BPM)	Very Slow (~18-33 BPM)	Largo (~31-56 BPM)
Largo	40 - 60	Extreme Drag	Grave Feel	Adagio
Adagio	66 - 76	Study Pace	Detailed Practice	Andante
Andante	76 - 108	Heavy Feel	Relaxed Groove	Moderato
Moderato	108 - 120	Ballad	Standard Practice	Allegro
Allegro	120 - 156	Half-Time (60-78)	Comfortable (90-117)	Presto (150-195)
Vivace	156 - 176	Manageable	Upbeat	Prestissimo
Presto	168 - 200	Moderate	Fast	Blur

Frequently Asked Questions

This is an artifact of the Time Stretching algorithm. To maintain pitch while slowing down time, the software splits the audio into tiny "grains" and overlaps them. At extreme settings (below 0.7x), these overlaps become audible, creating a metallic or robotic texture. This is a trade-off for keeping the correct musical key.

Yes. Unlike many simple players, this tool includes an Offline Rendering engine. When you click "Export", the browser recalculates the entire audio file at the new speed and generates a high-quality WAV file for you to download.

Processing is done entirely in your browser's RAM. We recommend files under 50MB (approx 5 minutes of WAV or 45 minutes of MP3) to prevent browser crashes. Larger files may cause the tab to become unresponsive during waveform generation.

Yes, but with limitations. Decoding large audio files requires significant processing power. Modern iOS and Android devices can handle this, but the visual waveform interaction is optimized for touch. For the best precision when setting loops, a desktop interface is recommended.

Browsers block audio autoplay to prevent spam. You must interact with the page (click/tap) at least once. If uploaded audio is silent, check if the volume slider is up or if the file itself is valid. Try using one of the "Demo Tracks" to verify your system audio is working.