For those of you who can't get pocket guitar.app to make any sound I found an easy way to fix it. Up at the top there is a yellow bar which is the volume. If that bar isn't there that's your problem. If you don't see a yellow bar you have the volume off, even if the volume in "settings" is full, if the yellow bar is turned all the way down there will be no sound. To fix it put your finger about a centimeter to the right of the "settings" button and drag it right. There you go. Its easy to accidently turn the volume down really low when you're touching a fret near it so lots of you could have turned it off by mistake. If you have the yellow bar and still no sound make sure the volume is up in "settings". If it still doesn't work then try rebooting.