A Vamp plugin that produces a spectrogram from only the low-frequency content of a signal.
You supply a frequency range and a number of bins, and it returns a magnitude spectrum containing the requested number of bins, spanning the frequency range you asked for. It does this by first downsampling the signal to an integer multiple of the maximum requested frequency, then calculating an FFT of an appropriate size and returning a subset of its magnitudes.
This is only likely to be relevant to you if you have a recording at a high sample rate that also contains low-frequency information, so that you want to separate the low frequencies from the rest of the signal. Commercial music/audio recordings normally do not contain any useful information below the range shown in a conventional spectrogram, although you could still use this plugin to isolate their low-frequency audible content. And if your recording is already at a low sample rate, as might be the case for a pure infrasound recording, any spectrogram plugin should be able to show the content.
Note: I made this because I wanted to investigate a couple of things and because we've had a few requests for infrasound visualisation in Sonic Visualiser. I don't actually know whether this is useful though. If you think it is, or if you think it isn't and you want to tell me why, drop me a line!
Further note: If you are looking to identify lengthy repetitive patterns in music, such as beats or tempo-synchronous changes, then this plugin is not what you want. You probably want a tempogram instead.