That is achievable. Post in Security, there are too many issues that do not work well in general fora when doing eicipherment and decipherment. Provide any additional details that are known and as well:
Is this a student project or is there any actual value to be protected.
How strong of encipherment do you actually need.
Is there a way to ensure the keys will not be lost or do we need a mechanisim that can be broken with sufficient effort.
Of course, by asking for details do not in any way reveal anything about the actual data or where the application would be used except in a generalized, concocted setting - and then only to model the security challenges.
If this is just for fun, say so.
"The differential equations that describe dynamic interactions of power generators are similar to that of the gravitational interplay among celestial bodies, which is chaotic in nature."
The standard JCE API in the javax.cypto package should be able to encrypt and decrypt what you have. It is designed to encrypt/decrypt binary data, so should handle voice data. It is designed to encrypt/decrypt buffers, so you will have to read and write the files.
And if you have Java 1.4 or later, it should be part of the Java core.