As an example, if a sound source produces a single frequency tone (e.g., when you make an ‘oo’ vowel sound* with your voice), the periodic motion of every atom and molecule in the sound bubble will be of that same single periodicity and that single vibration will be passed on with each collision that occurs. On the other hand, if the sound is complex, with a multiplicity of vibrational frequencies (e.g., if you make an ‘ee’ vowel sound**, which is quite complex and rich in harmonics), the atoms and molecules will each carry this complex array of periodicities/ frequencies.
*An ‘oo’ vowel sound with pursed lips is largely devoid of harmonics because the resonating cavities of the mouth and nasal passages are mainly not involved.
**An ‘ee’ vowel sound made with the mouth open involves the entire mouth, teeth, tongue, and paranasal sinus cavities, giving the sound a rich complexity of harmonics unique to each person.
To better visualize how a single atom can carry such complex periodic motions, imagine holding an apple and moving it slowly back and forth. (Let’s say that the apple represents an atom in the air surrounding your larynx).
Next, imagine quickly wobbling the apple as it moves slowly back and forth. The apple/atom is now vibrating in two different ways simultaneously. Now imagine that same principle extended until the apple/atom is vibrating in a hundred different ways simultaneously. (Not easy to imagine, but I think the point is made). This is how atoms and molecules carry all the vibrations and uniqueness of a voice or sound.
When an atom bumps into its nearest neighbor, all those vibrations transfer to the neighboring atoms.
The human voice, whether in speech or singing, is a good example of a complex sound source that contains many frequencies. What begins in the larynx as a small pressure (fairly monotone) spherical pearl of sound energy rapidly expands into the mouth and sinus cavities, where complex nuances are added by the tongue, lips, and resonance of the sinus spaces, adding to the complexity of the vibrations and forming a given word or sound.
The word began as a thought, but now that thought has been transcribed into a sound bubble that emerges from the mouth and nose. Its outer spherical edge shimmers due to every atom and molecule vibrating in unison. If you have a cold and your nose is blocked, the bubble emerges with a different tonal quality, and the character of your voice will be modified accordingly. But either way, the data in the bubble is, effectively, an amplified thought.