Well the best all round tool is certainly baudline. It's expressedly made for real time spectrum analysis ,noise measurement of all kinds .. i mean it's worth quite a long look. Trying it might get you hooked. The best the sound card the more you'll get out of it. http://baudline.com/ it's free :) Ric Baudline is a real-time signal analysis tool and an offline time-frequency browser. It has a built in tone generation capability and it can play back audio files with a multitude of effects and filters. Designed for environmental analysis missions that range from modulation parameter measurements to searching for transient signals that go bump in the night, baudline combines fast digital signal processing, versatile high speed displays, and continuous capture tools for hunting down and studying elusive signal characteristics.