Android 2.3.5 and above.
Sound You Can See !
Sound View is a Audio Spectrum Analyzer App. It analyzes sound from the built in microphone, or from an attached external microphone, and displays both the input signal, and the results of the spectrum analysis. The input signal is displayed in the lower view as a waveform and the spectrum is displayed in the upper view as bars indicating the strength of that frequency within the input signal.
Frequencies range from 0 hertz to 22000 Hertz or 22K, this is the range of the device microphone, and also the general range of human hearing.
You can double tap either the spectrum bars, or input waveform to display only that view, fullscreen. Another doubletap will return the display to showing both spectrum and waveform. Both portrait and landscape mode are supported.
A single tap will hide and display the navigation bar & scale info.
By selecting the settings button, the Settings view appears.
The magnification slider allows you to control height of the spectrum analyzer bars. Depending on the number of bars configured each spectrum bar represents a different number of frequencies, and therefore its value varies with the number of spectrum bars. Ideally the spectrum bar height would indicate the decibel level of that frequency, however each bar represents a range of frequencies, and it's value is a sum of their decibel levels.
The decay rate slider allows you to control how fast the bars fall back to the bottom of the display. The control gives you full control, as the far left will let the value bar fall immediately, and the far right will not allow it to fall at all.