Adjusting The Sound's Tempo
You can change a sound's tempo by clicking the Sound Details Tab on the bottom of the window.  Each sound can be in one of two modes: Adjust To Project Tempo or Time Stretch By.  Select the drop down to change the mode to Adjust to Project Tempo if it's in Time Stretch By mode.

Adjust To Project Tempo
If the sound is in Adjust To Project Tempo mode, Mixcraft will time stretch the sound based on the difference between the project's tempo and the sound's detected tempo.  For example, if the project tempo was 120 bpm and the sound's detected tempo was 60 bpm, it would time stretch the sound to be half as long, because it would be playing the sound back two times as fast.

However, you can have more than one tempo change in a project.  For example, in a transition between two songs, you could slowly ramp the tempo up with multiple tempo changes..  In this mode, the sound keeps perfect synchronization and adjusts the playback rate based on the latest tempo change.

Changing The Tempo Of A Sound
Assuming that the detected tempo of the sound is correct, you can change the tempo of a sound by adding markers with tempo changes.  You do not need to change the detected tempo of the sound, but, instead you should change the project tempo or add tempo markers!  In short, if you want to speed up the sound, increase the project tempo!  Changing the detected tempo of a sound should only be done if the detected tempo of the sound is wrong!

Changing The Detected Tempo Of A Sound
You must be in Adjust To Project Tempo mode to change the detected tempo of a sound.  

If the sound's detected tempo is wrong, you can adjust it via the Detected Tempo drop down control.  The original detected tempo will show up with an * next to it in case you need to restore it to the original detected tempo.  

*** Audio Clips only ***

The following information is for audio clips only.

Sounds longer than 30 seconds will show the actual beats in the Loop Editor.  This can be extremely useful as each beat will show a tempo at that beat point.  Most songs do not keep a constant beat and drift, in addition to having varying tempos, keys and time signatures.  Therefore, you can trim a sound and use a tempo within that trimmed area.  

Learn How To Fix Songs With Drifting Tempos here.

In fact, you can set the detected tempo to the average tempo within the active loop by clicking the Use Average Tempo In Active Loop button! 

Use Average Tempo In Active Loop button

In some cases, the detected tempo is off by a factor of two.   To quickly adjust the tempo by two, click the Double Or Half Tempo button! 

Double Or Half Tempo button