If you're on Windows, I've seen a few spectrogram skins for Rainmeter that uses whatever audio is being played on the device. For example, there is AudioAnalyzer[0]. Personally, I've been using a skin that shows a simple waveform of the current system audio, but also integrates with Spotify to change the color to match the primary album color. Unfortunately, I don't have the name or link on hand.

0: https://forum.rainmeter.net/viewtopic.php?t=31091

Run a soundcard loopback into an instance of izotope insight (or similar).