If the distance between musicians is large enough, listeners may perceive waves to be out of phase.
Typically, in this case, listeners perceive that one section of the band is playing their parts slightly after another section.
These findings indicate that listeners can perceive both happiness and sadness concurrently.
Both cuts and taps are essentially instantaneous; the listener should not perceive them as separate notes.
The slide is generally a longer duration ornament than, for example, the cut or the tap and the listener should perceive the pitch changing.
Of course, this doesn't mean that individual listeners perceived no differences or thought they did.
What matters is how the listener perceives the speaker's intention.
In other words, the term is meant to avoid any implication that the listener can perceive two keys at once.
However, if the listener perceives the direct sounds, he fulfils the mitzvah.
For example, different instances of sounds that human listeners perceive as the same may have very different waveforms.