We don't have "recording volume" in Voxie, but it is something we are considering for a version update. Until we have that, this is what we suggest if your recordings sound muffled or weak when being played back:
We have found pretty considerable differences in sensitivity from iPhone to iPhone. You can use a higher audio quality setting, but that's also going to create much larger files. So this isn't a good idea if you email your files a lot. If, however, file size doesn't bother you, try medium or high (or CD but that makes huge files) and see if that at least helps. This will mainly help with the fidelity of the recording and reduce the "lisp" noise in a recorded voice.
Make sure your volume is all the way up when you're playing back the recording.
The mic is on the bottom of the iPhone. So don't cover this part when making a recording or brush the bottom of the iPhone against something as you'll hear that in your recording.
Of course, having the mic closest to you when speaking helps the most (the mic is on the bottom of the iPhone).
And finally you can use an external microphone such as the Apple earbuds with integrated mic that came with your iPhone. You can also purchase for your iPod Touch 2nd Gen if they didn't come with your iPod. Look on the Apple Store online for their earbuds with integrated mic.
Note that the level indicator on the recording page does not need to be full for you to get a good recording. It's mainly there to tell you that the mic is live and that you are still recording. Even if you only get a 1/5th level, you're still going to have a good recording.