ignoring background noise java sound

[Tony May]

Hi All,
I am looking to record from the sound-card to a WAV file using java-sound (so far so good). My problem is that the sound is coming from a microphone and I only want to record noise once it reaches a certain level,basically ignoring background noise and only recording when someone starts speaking directly into the microphone !
Has anyone got any ideas ? Can it be done ?
many thanks
Tony May