GoldWave Manual

Time Settings
Setting	Description
Change (%)	Sets the relative change in time. A value of 50% slows down time, stretching the sound. A value of 200% speeds up time, shortening the sound.
Length (s)	Sets a new length for the selection. Use this to make a sound fit a certain time, such as squeezing a 35 second radio commercial into a 30 second spot. The new length must be from one quarter up to four times the original duration of the selection. Settings beyond that range cannot be processed.
Algorithm	Three different time altering algorithms are provided, each with certain advantages and disadvantages: `Speed` simply changes the sampling rate of the entire selection 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. In other words, if you were to speed up a voice, the pitch becomes higher, making the voice sound like a chipmunk. `Similarity` uses correlation to add and overlap small, similar sections of the sound. This technique preserves the pitch. It generally produces high quality voice and fair quality music when using small speed or time changes. A fair amount of time may be require for processing, depending on the Search range value. For voice, the `Window size` should be set between 30 and 40 and the `Search range` set to between 10 and 20. For music, a larger `Window size` and `Search range` gives better results, such as 60 and 30. Larger `Search range` values increase processing time and echo. Low values increase gurgling noise. `Overlap` adjusts the amount of overlap between sections. Correlation is used to find the best matching sections to overlap, then the sections are crossfaded to reduce rough transitions from one section to the next. A value around 40% is recommended. Larger values may increase echo and significantly increase processing time. Values below 20% may cause distortion and gurgling due to shorter correlation and crossfade lengths. `FFT` uses Fast Fourier Transforms and interpolates or decimates the frequency analysis to change the length. This technique preserves the pitch, but can cause some echo artifacts in the sound. Best quality is obtained by using the Oscillator synthesis option, but that requires significant processing time. The `FFT size` should be set from 11 to 12 and the `Overlap` may be set to 4x for fastest processing, but 8x or 16x may give better quality. The `FFT size` and `Overlap` settings are explained in the Effects Overview section.

Speed simply changes the sampling rate of the entire selection 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. In other words, if you were to speed up a voice, the pitch becomes higher, making the voice sound like a chipmunk.

Similarity uses correlation to add and overlap small, similar sections of the sound. This technique preserves the pitch. It generally produces high quality voice and fair quality music when using small speed or time changes. A fair amount of time may be require for processing, depending on the Search range value. For voice, the Window size should be set between 30 and 40 and the Search range set to between 10 and 20. For music, a larger Window size and Search range gives better results, such as 60 and 30. Larger Search range values increase processing time and echo. Low values increase gurgling noise. Overlap adjusts the amount of overlap between sections. Correlation is used to find the best matching sections to overlap, then the sections are crossfaded to reduce rough transitions from one section to the next. A value around 40% is recommended. Larger values may increase echo and significantly increase processing time. Values below 20% may cause distortion and gurgling due to shorter correlation and crossfade lengths.

FFT uses Fast Fourier Transforms and interpolates or decimates the frequency analysis to change the length. This technique preserves the pitch, but can cause some echo artifacts in the sound. Best quality is obtained by using the Oscillator synthesis option, but that requires significant processing time. The FFT size should be set from 11 to 12 and the Overlap may be set to 4x for fastest processing, but 8x or 16x may give better quality. The FFT size and Overlap settings are explained in the Effects Overview section.

Time