Do not backup or sync your phone after you have lost your files. You risk overwriting your backup that contains the lost files.
iTunes makes a backup of your devices data each day when you sync your device with your computer. This backup contains your devices settings, and some application data. iRecorder recordings are backed-up with the phone backup.Learn more about iPhone and iPod touch backups
Backup extractor is a utility program for Mac OS X that can be used to "extract" the files from iTunes backups without restoring an entire backup to your device. This is helpful if you are just trying to recover a few lost files.
There is also a Backup extractor utility for Windows available that may also help Windows users recover files from your iTunes backups.Download Back-up Extractor for Windows