record audio system stream on a mp3 file

[Aldo85]

Hi all,
I'm try to catch audio stream of operative system, code in mp3 format and save it in a file, with a pipeline, how can i do this?
I've tried with this:

gst-launch-0.10 -v alsasrc ! volume volume=9 ! audioconvert ! audioresample ! audio/x-raw-int,rate=44100,channels=2 ! lame name=enc mode=0 bitrate=160 ! filesink location=/output.mp3

It doesn't return error but palying it, you can't hear nothing.

Please help me.