RHY.2:5.3 - A smooth sound has a rhythmic shape

A continuously sounding tone has a changing amplitude envelope. Consider two constructed envelopes over two seconds. A completes one smooth rise-and-fall cycle; B completes two. Both remain audible throughout, with the same beginning and end of the tone.

The receiving question is which modulation repeats once per second. A list containing only the tone’s start and stop gives the same answer for both and cannot resolve the question. Retain the course of amplitude change, or its modulation period when that summary suffices: two seconds for A and one second for B. B has the required repetition period. The tone’s attack list remains useful for onset questions.

This construction establishes the stated envelope difference, not what a listener feels as a beat. For a question about that response, retain the listening conditions and obtain the response relation; the envelope period alone does not supply it.