Spectrumview audio spectrum analyser

When I got my iPhone SE about a year ago, I was quite surprised to see that an app was still available for Spectrumview from Oxford Scientific. 

This is available in iOS but I don't think it is available for Android. Many years ago it was useful for VLF and lightbeam work when I needed an audio spectrum analyser. It was also going to be used at 137kHz until I blew up my beacon earlier this year! By changing the sample rate you can adjust the time shown on the screen.

It is the best audio spectrum analyser I found. It is a free app.