I'm checking into this sleepy forum to tell you about some software that runs on iOs devices. It's great to have tools like this in your pocket!
There are a number of real-time spectrogram programs you can look at for your iPhone or iPad , just search for Spectrogram and you'll find a few. I like Spectral EyePro because it lays out the spectrum in a logarithmic spiral, which just happens to be the same way I visualize intervals in my program Droneo.
Droneo is a drone synthesizer which lets you specify eight simultaneous droning voices. The pitch of each voice is made from a interval over a shared base pitch. These intervals can be specified in cents, as just ratios, or as degrees of equal divisions of other intervals. It itself has a number of timbres, including timbres that change their harmonic content randomly over time. It fits in well with this community of overtone singers and players. It was featured in Pauline Oliveros' Droniphonia (2009). Take a peek: Droneo Website