Maybe he wants to know what a spectrum analyzer is? The latter is an oscilloscope that displays across the screen all the frequencies within its design range. It shows which radio signals are present at what place in the spectrum (hence the name) and at what strength. Usually they can be tuned and narrowed down in width (frequency) so as to pick out and magnify one signal to see what the output of a device looks like and whether it is putting out garbage, etc.
They work by having an oscillator that sweeps across the range in the manner of a radio receiver whose tuning knob is being whirled back and forth so quickly that, through the persistance of the 'scope tube and your eyes*, you can see everything in the range covered. They are expensive and the higher they go, the more costly they are. There have been some reasonable 'scope probes made that, with a 'scope give a miniature poorman's version.
Basically it's for radio work, but it could also apply to audio (it used to be hard to build an audio receiver, but probably not now). Usually you just look at the screen and see what there is to be seen, but I imagine nowadays there is all kinds of calculating power available to be applied to the signals and the prices would be astronomical.
Of course if you really want to know the truth of the matter, you would just read
where else?.
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*I suppose they could digitize and store it all so that persistance is not a factor. The 'scope would just play it back and wouldn't have to be very fast.