Time Warp

Menu Command: Effect | Time Warp

Changes the playback speed or stretches/compresses the length of the selection. The Change value lets you specify a relative change in percent. A value of 50 makes the selection play twice as slow. A value of 200 makes the selection play twice as fast. The Length option lets you specify a new length for the selection. This is useful if you need to make a sound fit a certain time, such as squeezing a 35 second commercial into a 30 second spot.

Three different time altering algorithms are provided, each with advantages and disadvantages.

Rate

Changes the sampling rate of the entire sound so that it plays back at a different speed, similar to spinning a vinyl record faster or slower. It works the same way as the speed fader in the Control window, but in this case, the sound itself is changed. This technique is very fast and produces excellent quality. However, the pitch of the sound is changed as well.

Similarity

Uses correlation to add or overlap small, similar sections of the sound. This technique preserves the pitch and generally produces high quality for voice and fair quality for music, when using small changes. A large amount of time may be require for processing, depending on the Search range value. For voice, the Window size should be set between 20 and 30 and the Search range set to between 5 and 10. For music, larger Window size and Search range values give better results, such as 100 and 25.

FFT

Uses Fourier transforms and interpolates or decimates the spectral analysis to change the length. This technique preserves the pitch, but can introduce some artifacts into the sound. Best quality is obtained by using the Oscillator synthesis option, but that requires significant processing time. The FFT size should be set to 11 or 12 and the Overlap should be 4x, but may be 8x or 16x for slightly better quality.

Note: If you changed the Control window playback speed fader, remember to set it back to 1.00 so that the sound plays at the correct speed.