Very nice spectrum analyzer – Audio Spectrum Analyzer Review

Unlike many other spectrum apps, this one allows some configuration. You can select the window type, peak hold average, and number of spectral lines, among other things. You can't select a maximum frequency other than the highest possible (I guess because this would require a down sampler and digital filter), but since it lets you pick a very high number of spectral lines, you can window the results to get what you need and still have reasonable resolution. We use it for quick and dirty measurements when we don't want to set up the high dollar gear. For example, we recently used it to determine blade natural frequencies (or at least the first one since it radiated significant sound) for an axial compressor to select which should be adjusted to meet the spec. This saved the project many hundreds of dollars in setup time for each blade. We used our high tech gear to get the final data, but this app was great for the initial cuts. I'd give it five stars, but I'm saving the extra star for when they update to provide a linear vertical axis and perhaps more control over FFT parameters.
Review by smplee on Audio Spectrum Analyzer.