Sounds to me pretty easy
Sorry it is not.
The Arduino has very little memory and no D/A converter. So you have to built those on. You require an SD card and a D/A. The simplest way to get these is an Adafruit wave shield. You would also need a microphone and amplifier, to feed the signal into the A/D.
You should be able to do your project with this extra hardware. It is possible to kludge an A/D but in my opinion it is not worth it.
This link covers what you need to do:-