In one aspect, an example method for outputting an alert indicating a functional state of a back-up audio-broadcast system involves: a computing device receiving a first audio-stream that represents first audio-content; the computing device generating a first signature based, at least in part, upon an extent of single-channel/multi-channel transitions included within the first audio-content; the computing device receiving a second audio-stream that represents second audio-content; the computing device generating a second signature based, at least in part, upon an extent of single-channel/multi-channel transitions included within the second audio-content; the computing device making a determination that the generated first-signature and the generated second-signature lack a threshold extent of similarity; and responsive to the determination that the generated first-signature and the generated second-signature lack the threshold extent of similarity, the computing device outputting an alert.