Roblox - Plane Crazy - Reactor event (Meltdown and startup also read description) 

1. Get the speaker. 2. Click on configure to edit. 3. Look at the bottom, there's a bar that says Fade. 4. If you set the fade to maximum (25) and set the pitch to 10, it will take 25 seconds to reach 10 pitch. So basically the pitch will start from 0 and take 25 seconds to reach 10. You can adjust the bar. The lower the fade is, the faster it will reach 10 pitch. This also depends on the pitch; if you set it to 5 (Example) it will take the amount of seconds that you have set in the fade bar to reach 5. That was all.

thank you for telling me how to

No problem