enhancements for broadcast FM (and other FM also)

[GoogleCodeExporter]

SDRsharp is a very usefull tool for little FM broadcasting radios. It already 
can be used to investigate troobleshootings in emitters.

Other point of interest for radio FM broadcaster are :

- FM excursion vu-meter and level display : 

The radio broadcasters have to control the FM excursion of their transmitters. 
The common maximum excursion in FM broadcasting (all around the world) is 75kHz.
for a vu-meter a good display should show excursions lower than or equal to 
75kHz in green color, and bigger values in red color.
it could be also interesting to display by text average and peak excursion 
level.

- MPX record output : 

the baseband spectrum is also a major point of interest for broadcasters to 
know if all type contents are properly modulated, and do not disturb each 
other. I am talking about the different subcarriers often seen in FM 
broadcasting: mono signal (0-16kHz), pilot tone (19kHz), stereo (22 - 54kHz), 
and RDS (54-64kHz). This kind of monitoring is very usefull to compare 
performance of FM broadcast sound processor. The baseband analysis can be 
easily monitored using freeware MPXTOOL (http://mpxtool.com/site/). MPXTOOL can 
read FM demodulated wave files (16bits PCM mono at 192kHz) or flac files. SDR 
sharp could be a great tool combined with MPXTOOL by providing FM MPX recorded 
files.

Original issue reported on code.google.com by [email protected] on 23 Apr 2013 at 6:59