How to increase the volume in an m4a file?

I have an m4a file. When listening to it on my iPod Touch, the volume is too low, even when I turn it all the way up.

I need to increase the volume in the file so that I can hear what is being said.

Also, in the background it sounds like there is a hissing sound that I'd like to get rid of.

2 Answers

I'd use mp3gain or AACGAIN for that. The former's GUI works with AACGAIN too, but AACGAIN is the app for m4as.

It'll let you batch modify the volume of files to a certain level without loss of quality.

You need to look at "Auto Volume Levelling". This is done on your PC/MAC.

This page has instructions for iTunes as well as other music apps.

Though if you've got a background hiss already, this could get louder too. You'd need to look at some more serious filtering software for that.