Really needs X-axis labels…   This app really needs time labels along the X axis.   Other than that, I am quite impressed.  My background in acoustical analysis would make this of interest to me, but I think even those without such a background would have to find this very cool.  I have a memory, from more than a quarter century ago, of being shown a waterfall plot, and hearing the sound that was represented, and having a light go on in my head about the relationship between what I was seeing and what I was hearing.  Back then, it took the better part of an hour for a pen plotter to draw the waterfall plot that I was shown.  I can imagine people today, watching this app on their phones in realtime, and having the same epiphany that I had back then.   About twenty years ago, I wrote a program like this to run on an MS-DOS-based computer, in realtime.  Back then, it took a specialized digital signal processor to handle doing the FFTs fast enough to make this possible.  Isn't it amazing how far the technology has advanced, since then, that this can now be done in a small, common, handheld device.

Great app I will give a star for each point implemented: 1. Subtracting of pre recorded spectrum(e.g. noise) 2. Lower sampling frequencies(e.g. 4kHz, 2kHz) 3. Saving of spectrogram in text Or higher resolution image with time marks Other than that this app is much more accurate than tons of others I tested.

Don't buy the full app stick with the free one I thought the free app was good. I kicked myself for forking out for the full version. Random signals and differences between devices asked for help was told to calibrate? Sent images of faulty traces but no reply since then. In short for me poor support, over priced app with very little extra for paying full price. Use the free one and stay happy.

Logarithmic scale is off The logarithmic scale feature which I paid good money for is not accurate. Middle C which appears a perfect 262 hz in the linear version appears to be 200hz or so. Also you cannot rescale to limit the plot to a particular octave. I want this app to be able to tell me which notes are being played in a piano chord, but I cannot trust the scaling - please fix this before I up my rating. It would also be a great help if you could rescale in musical notes, so that you can clearly see which notes are being played

Unfinished feel. Great idea mediocre implementation. Set an option you phone doesn't support and it'll not work... Restart the program before changing it back and you get an "unsupported configuration" error and an instant quit, making it then unusable.

The basics are great, range zooming very bad. It kind of works, but in an unpredictable way...you have to randomly mash your finger on the amplitude and frequency scales until something useful hopefully appears. 5 star app with range scaling fixed, particularly with numerical input. FFT works great, very fluid.