Physics · Sound

Pitch, Frequency, and Loudness / Intensity

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Wrap-up

What you learned

Recommended next: Open concept testCheck whether the core ideas are ready without leaving this concept.
Read next: BeatsUse pitch differences to hear interference envelopes

Key takeaway

Frequency sets pitch by controlling cycle timing, period, and compression spacing at fixed sound speed.
Amplitude sets the size of parcel motion and the bounded amplitude-squared loudness / intensity cue.
Moving the probe changes delay and phase at the listening point, not the source pitch or loudness.

Common misconception

A taller sound wave must have a higher pitch because the graph looks bigger.

Amplitude changes how strong the motion is, not how many cycles happen each second.

Keep this idea moving

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Hear superpositionSound

Beats

Superpose two nearby sound frequencies, watch the fast carrier sit inside a slower envelope, and connect beat rate to the frequency difference on one compact bench.

Motion and pitchWaves

Doppler Effect

Watch a moving sound source compress wavefronts ahead and stretch them behind, then see how source motion and observer motion combine to change the heard pitch on one bounded classical bench.

Sound superpositionWaves

Wave Interference

Superpose two coherent sources, trace their path difference to phase difference, and watch bright and dark regions emerge on the same live screen.

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More practice optionsReview on the bench · Worked examples

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Reference and support

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Equation snapshotTiming versus strength snapshot · Spacing at fixed medium speedShow 3 equations

Use the equations to keep three ideas apart: frequency sets period and wavelength at fixed sound speed, amplitude sets the bounded intensity cue, and probe position only shifts the timing of the sampled wave.

Timing versus strength snapshot
$f = \frac{1}{T}$
Higher frequency means more cycles each second, a shorter period, and a higher pitch.
Spacing at fixed medium speed
$λ = \frac{v _{w a v e}}{f}$
At fixed medium speed, a higher frequency means a shorter wavelength and more closely packed compressions.
Bounded loudness / intensity cue
$I_{c u e} \propto A^{2}$
This bench uses amplitude squared as a loudness cue, so larger amplitude means a stronger loudness cue without changing pitch by itself.

Why it behaves this way

Explanation

Pitch and loudness are different sound ideas. Pitch comes from frequency: higher frequency means more cycles each second, a shorter period, and tighter compression spacing at fixed sound speed. Loudness comes from amplitude and this bench's intensity cue, so a sound can get louder without getting higher in pitch.

Use the bench one knob at a time. Raise frequency to hear and see a pitch change, raise amplitude to strengthen the loudness cue, and move the probe only to change delay at the listening point.

Key ideas

01Pitch is set by frequency and period, not by amplitude.

02At fixed medium speed, higher frequency means a shorter wavelength and more closely packed compressions.

03Loudness follows amplitude and the intensity cue, while moving the probe changes delay rather than the pitch or loudness produced by the source.

Worked examples

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Frozen walkthrough

Step through the frozen example

Frozen walkthrough

These checks use the same sound-bench relationships from the lesson, so the numbers stay tied to one coherent setup instead of a detached worksheet.

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Example 1 of 2

Frozen valuesUsing frozen parameters

For a generated sound setup with $v_{w a v e} = 2.4 m/s$ and $f = 1.1 Hz$ , what wavelength and period go with that pitch?

v_{w a v e}

Wave speed

2.4 m/s

f

Frequency

1.1 Hz

λ

Wavelength

2.18 m

T

Period

0.91 s

1. Use the pitch relations

Use

λ = \frac{v _{w a v e}}{f}

and

T = \frac{1}{f}

2. Substitute the setup values

λ = \frac{2}{.} 41.1 = 2.18 m

and

T = \frac{1}{1} .1 = 0.91 s

3. Connect the result to the sound you hear

A frequency of 1.1 Hz sets the source repetition rate, so pitch is set by timing while the spacing becomes 2.18 m.

Generated pitch quantities

λ = 2.18 m, T = 0.91 s

The frequency sits in a middle range here, so the pitch cue is moderate and the cycle timing is neither especially slow nor especially fast.

Quick test

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Accessibility

Open the text-first descriptions when you need the simulation and graph translated into words.

The simulation shows a horizontal sound tube with a source piston, parcel markers, a movable probe, and a colored compression ribbon. Optional overlays mark motion direction, compression spacing, and a bounded energy-transfer cue.

Changing frequency changes how quickly the sound repeats and how closely the compression pattern is spaced. Changing amplitude changes the parcel swing size and the linked intensity cue.

Graph summary

The first graph compares source and probe displacement over time so pitch stays tied to frequency and period.

The second graph compares the probe shift with the local compression cue.

The third graph shows the bounded intensity cue as a function of amplitude.

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Starter track

Step 2 of 5

Sound and Acoustics

Pitch, Frequency, and Loudness / Intensity appears later in this track, so it is cleaner to start from the beginning first.

Previous step: Sound Waves and Longitudinal Motion

Also appears in Waves.

Start from track beginning