Frequency: This refers to how many sound waves pass a point in a given time. Higher frequency corresponds to a higher pitch. Sounds with very high frequencies are perceived as shrill or piercing.
Intensity: This refers to the amplitude of the sound waves, essentially how much energy they carry. Higher intensity means louder sounds. While a sound can be high frequency without being loud, loud high-frequency sounds are particularly likely to be perceived as shrill.
Other factors:
* Timbre: This refers to the "color" of a sound, determined by the mix of different frequencies present. Some sounds can be shrill even at relatively low frequencies if they have a particularly harsh timbre.
* Context: What is considered "shrill" can also be subjective and depend on context. A sound that might be pleasant in one situation could be perceived as shrill in another.
Examples of shrill sounds:
* A high-pitched whistle
* A screeching car brake
* A screaming child
* A ringing alarm clock
In short, a shrill sound is a high-pitched, often loud sound that can be perceived as unpleasant or piercing.