The Java Cryptography Extension (JCE) extends the JCA API to include APIs ... The Java Cryptography Architecture (JCA) was designed around these principles: ... [ May 11, 2008: Message edited by: Nicholas Jordan ]
As a student project, the rules are a lot easier to deal with.
First, make sure you can record voice and store the data, at least to a disk file. And can play it back.
Get that working first.
Then you can 'encipher' it by XOR with a trivial passphrase. Store that, and play it back.
Then, and only then, add the real crypto layer as Henry and others have pointed.
The key to remember is that a crypto API takes stuff and makes it look like random garbage. It does this when it works right, and when it works wrong. If you don't have everything else working, you will never be able to tell what is the cause of your bugs.
Its fairly easy to get things a little bit wrong, and if you are lucky, you won't be able to decihper it. If you are unlucky, you will deploy it, and later someone else will find that its trivial to break.
For a student project, you don't have to worry too much about that.