Audio how to record just a part of an audiosource?

Hi everyone,
I´m trying to record a wav file just when the microphone signal exceed a sound pressure level given. So far I´ve implemented the sound level meter and it works fine, but the problem is I´m recording even the silences, that is, the whole audio signal. Probably I need a second clip but, how to split the audiosource into two clips? Any ideas?
I attach the code.
Thank you in advance.