TimeStretch Player is a small online tool that allows you to change the speed and tone of audio files and even create a loop from an excerpt from your music file.
To start, you must open an audio file in TimeStretch Player by selecting it using the "open Track" button or by dragging and dropping it on the application page. The supported format is the MP3 and OGG. On Android, you need to use an application that can provide an audio file, for example, Google Drive.
After selecting the file, TimeStretch Player will display the waveform of the track in seconds. To play the audio track, you can simply click the Play button or press the SPACEBAR on your keyboard. To move to a specific location, drag the yellow playback bar with your mouse or click the waveform location.
Then you have to turn one of the 3 buttons (Speed, Pitch, Tune) to edit your audio file. For example, the pitch button is used to change the height in notches of 1/2 ton.
To loop a passage from your audio file, simply click on the Loop button (2 arrows rotating in circles)). To select the beginning and end of the loop, you must click the [and] buttons.
Finally, a volume button allows you to reduce (but not increase) the volume of your music file.
After your settings are complete, you can save the end result in WAV format to your computer.
link : TimeStretch Player