The Audio Analizer app is a free Android app for tracking your songs. This app has a chart that displays the loudness of the sound in dB as a function of the frequency in Hz. There is a button for starting and stopping the recording and an indicator for signal (weak, normal and overload). What I found really useful about this app is that it is comparable to the human ear. When on a stage you can detect if the speakers are too loud and can damage your hearing and if you go in the crowd (where the crowd will be actually) you can see how loud they can hear the music. Based on these two meawurements you can decide how much to turn up the volume knobs and to calibrate all the instruments on stage to be heard well from all the points in the crowd. You can set the app to keep screen on, to generate and display certain frequencies, to show either the spectrum bands only or the full spectrum, set the spectrum dynamic range, set the output channel, to set the output attenuator, set the FFT size, set the frequency scale, set normalization, set output pulse duration, set delay time and digital source. The Audio Analizer app is a really well made app that could even help with tuning an instrument, but you should use it for other things, for the better.