How do you define each loudness, pitch, and timbre? Name one potential perceptual effect each of the above can create in a film.
Loudness, pitch and timbre are words that are always confused, so this is a good question. Let's just get the definitions for the three straight.
Loudness is, very simply, how loud something is. When you turn up the volume on your stereo or click the volume on your TV, that's altering the loudness of the sounds you're hearing. When it comes to music, the term dynamics refers to loudness; dynamic shifts are when the loudness changes.
Pitch, on the other hand, is a little more complicated. The easiest way to think of it is with a piano: every key you press alters the pitch. If I press the C key on the piano, then the D key, I have changed the pitch of the note I played. All sounds have pitches, whether they're musical or not. This is changed by the frequency of the sound wave. Ultimately, pitch is not quite as simple as A-B-C-D-E-F et cetera, but that's a good way to understand it. Pitch is just the note of the sound, basically.
Timbre is the least concrete of these three, in my opinion. It is how a sound sounds. I can play a C on a piano or on a guitar, and the difference in how these two notes of the same PITCH sound is their TIMBRE. It completely changes how a note or a sound feels.
For loudness, one obvious perceptual effect that could be in a film is the emotion of a scene. If a character is talking, then transitions to yelling, their loudness has changed, and we will know that there is a change going on in how they are feeling.
For pitch, think about horror movies. If there is a pleasant major chord being played in the background, things won't be all that creepy. If the music in the back instead uses a minor chord, our minds will be ticked off to something being off or wrong, which makes it creepy. This would be a change in pitch.
For timbre, let's think about a character walking down a hall. If their steps sound empty and hollow and don't echo much, we will understand the hall is smaller. It it echoes a lot, this will show that the hall is bigger and perhaps suggest a feeling of loneliness or emptiness. This is a difference in how the sound sounds and feels, which would be timbre.