Frequency is a physical property of a wave — how many cycles happen per second, measured in Hz. Pitch is what your brain does with that number: higher frequency generally sounds like higher pitch. Frequency is measured with instruments; pitch is a perception.
Amplitude is the size of a wave's pressure swing — a physical, measurable quantity. Loudness is how big that swing feels to your ear. In practice, loudness is measured in decibels (dB), a scale built specifically around how human hearing actually works.
Human ears can typically detect frequencies from about 20 Hz to 20,000 Hz (20 kHz). Below that range is infrasound — real vibration, just too low-frequency for us to hear as a tone. Above it is ultrasound — same idea, too high-frequency.
Drag through the frequency spectrum and see where common sounds fall relative to the human hearing range.
The decibel scale is logarithmic, not linear. Equal steps in dB represent equal multiplications in physical intensity, not equal additions.
Compare two decibel levels and see the gap between what's physically happening and what your ear reports.
Set B to 20 dB above A — physically that's 100× the intensity, but it only sounds about 4× as loud. That gap is the whole point of the decibel scale.
| 0 dB | Threshold of hearing |
| 30 dB | Whisper |
| 60 dB | Normal conversation |
| 85–90 dB | Hearing damage risk with prolonged exposure |
| 110 dB | Loud concert |
| 130+ dB | Threshold of pain |
You now have a full perceptual vocabulary for sound: frequency and pitch, amplitude and loudness, and the decibel scale that ties loudness to real numbers. Project 3-1-3 will have you chasing frequency by ear as you tune an instrument; Problem 3-2-1 will have you reasoning about decibels to diagnose a real noise complaint.