Audacity: Change audio speed and keep the pitch of the talker unchanged

If the speed of a sound file is increased, the pitch is also increased. This experiment can be easily made using Audacity.

Select Effect/Change Speed to change the speed of the sound file.

Increase the speed by 50% in this example.

The sound file is shorten to 2/3 of the original length.

By playing the new sound file, the pitch of the sound is increased. This phenomenon is known as the chipmunk effect. In the very early video clip for Chip 'n' Dale, "Private Pluto" video clip in 1943, the voices of the two chipmunk roles were produced by speeding up normal speech. (Wikipedia)

If we want to speech up without changing pitch to higher frequencies like chipmunks, simply choose Effect/Change Tempo instead.

Adjust the tempo by 50%.

Results:

The 1.5x tempo speech file sounds similar to the original file in pitch, but much faster.

Zoom in to show the oscillations in waveforms and frequencies in spectrograms:

Reference:

How to Change Speed in Audacity Without Chipmunk Effect! Change Speed in Audacity! Speed up Audio! (YouTube)

聽力實驗常見的鼠類及相似動物(Photos for chipmunk and similar animals)

Audacity: Change the sample rate from 44.1 kHz to 16 kHz (StudyEECC)