I think you are looking for an op-amp. For instance they are used in peak charge detection systems of r/c electric cars. If I have it right, not sure of that, they continously compare two signals and output a value based on that comparison. The reference signal can be steady or dynamic.

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op-amp

You may need some way to average the response time of a circuit like this. You could wind up with every bump causing a thump in the speakers.