Change Tempo vs Change Speed in Audacity

In Audacity, both "Change Tempo" and "Change Speed" alter the duration of an audio track, but they treat pitch very differently. While Change Speed affects both playback rate and musical pitch simultaneously, Change Tempo adjusts the playback speed while keeping the original pitch intact. Understanding this fundamental distinction ensures you choose the correct tool whether you are editing a podcast, aligning musical tracks, or creating sound effects.

What Is Change Speed?

The Change Speed effect alters the duration and pitch together, simulating the mechanical effect of playing a vinyl record or analog tape faster or slower than its recorded rate.

• How it affects pitch: Speeding up the audio raises the pitch (creating a high-pitched "chipmunk" sound), while slowing down the audio lowers the pitch.
• Audio quality: Because it simply resamples the audio, it causes virtually no digital artifacts, stuttering, or robotic phasing.
• Best use cases: Correcting playback speeds on digitized cassette tapes or vinyl records, fixing audio synced to video framerate conversions (e.g., PAL to NTSC), or creating dramatic comical or deep voice sound effects.

What Is Change Tempo?

The Change Tempo effect modifies the duration, rate, or beats per minute (BPM) of the audio without altering its pitch. It uses time-stretching algorithms to stretch or compress the sound waves without transposing the musical notes or the natural tone of a speaker's voice.

• How it affects pitch: The pitch remains completely unchanged, regardless of how fast or slow you make the track.
• Audio quality: Because it relies on mathematical time-stretching, extreme changes can introduce noticeable digital artifacts, such as echoing, metallic reverberation, or stuttering.
• Best use cases: Adjusting the length of a voiceover to fit a strict broadcast window, speeding up a podcast for faster listening while keeping the host's voice natural, or matching the tempo of different musical samples without transposing keys.

Quick Comparison

To maintain a speaker's natural tone or a song's original key while adjusting duration, use Change Tempo. If you want a clean, artifact-free stretch and do not mind—or actively desire—a pitch shift, choose Change Speed.