After searching on why my m4500 couldn't use the microphone I found out all the stuff about alsa.
1) A few web pages state 'let us know' if you find a configuration that works for your machine....but IT DOESN'T SAY WHO TO TELL! eg Reporting Problems in  http://www.alsa-project.org/main/index.php/Help_To_Debug_Intel_HDA and http://www.alsa-project.org/main/index.php/Help_To_Debug
2) Anyway, I have those details for the m4500 so I am posting them here. This fix solved my internal microphone not working.I added 'options snd-hda-intel model=dell-s14' to the alsa-base.conf. I didn't try many others.
I attach the files which are meant to be helpful for someone!
Regards,adam