Sound: Frequency and Pitch

• Sound is a mechanical wave resulting from an object's vibration.
• Vibration causes the motion of particles in a medium, propagating energy.
• Sound needs a medium to travel, it cannot travel through a vacuum.
• Sound travels at varying speeds depending on the medium.

Frequency

• Frequency is the number of complete wave cycles per second.
• Measured in Hertz (Hz); 1 Hz equals one cycle/second.
• Higher frequency means more cycles per second.
• Frequency is an objective, physical sound wave property.

Pitch

• Pitch is the perception of a sound's highness or lowness.
• It is a subjective, psychoacoustic property.
• Pitch relies on the frequency of a sound wave.
• Higher frequencies typically result in higher perceived pitches.
• Lower frequencies are perceived as lower pitches.

Relationship between Frequency and Pitch

• Frequency and pitch are not the same, though related.
• Frequency is a measurable physical attribute, while pitch is a subjective experience.
• Strong correlation exists between frequency and pitch.
• Changes in frequency lead to changes in perceived pitch.

Factors Affecting Pitch Perception

• Sound intensity (loudness) can slightly affect perceived pitch.
• Very loud sounds may seem slightly lower in pitch.
• Harmonics and overtones in a complex sound influence pitch perception.
• The human ear has sensitivity to frequencies, 20 Hz to 20,000 Hz can be heard.

Human Hearing Range

• Typical human hearing ranges from 20 Hz to 20,000 Hz.
• Range decreases with age and noise exposure.
• Most sensitive range is 2,000 Hz to 5,000 Hz; important for speech.

Ultrasound and Infrasound

• Ultrasound is above 20,000 Hz, beyond human hearing; used in imaging, sonar.
• Infrasound is below 20 Hz; generated by earthquakes, eruptions.

Musical Notes and Frequency

• Musical notes link to frequencies.
• Western music uses equal temperament tuning.
• Octave divides into 12 semitones.
• Semitone frequency relates to the previous one by the twelfth root of 2 (≈ 1.05946).
• A4 (A above middle C) usually tunes to 440 Hz.

Octaves

• Octave is the interval between two notes with a 2:1 frequency ratio.
• A note at 440 Hz is one octave lower than 880 Hz.

Harmonics and Overtones

• Sounds comprise multiple frequencies.
• Fundamental frequency is the lowest in a complex sound.
• Harmonics are integer multiples of the fundamental frequency.
• Overtones are any frequencies above the fundamental.
• Harmonics are a subset of overtones.
• Amplitudes of harmonics/overtones shape timbre.

Timbre

• Timbre distinguishes sounds with the same pitch/loudness; also known as tone color/quality.
• Timbre depends on harmonics, ADSR envelope.

Applications of Sound, Frequency, and Pitch

• Music relies on sound, frequency, and pitch.
• Communication: Speech changes pitch and frequency to convey meaning.
• Ultrasound imaging uses sound waves to see inside the body.
• Acoustics studies sound in architecture, engineering, and environment.
• Sonar relies on sound waves to locate underwater objects.

Sound Intensity and Loudness

• Sound intensity measures energy flow per area (W/m²).
• Loudness is subjective perception, measured in decibels (dB).
• Decibel scale is logarithmic; 10 dB increase means tenfold intensity increase.
• The threshold of hearing is 0 dB.

Doppler Effect

• Doppler effect shifts in frequency due to source/receiver motion.
• Approaching source raises perceived frequency/pitch.
• Receding source lowers perceived frequency/pitch.
• Doppler effect has uses in radar, sonar, and astronomy.

Interference

• Sound waves exhibit interference.
• Constructive interference (in phase) raises amplitude/loudness.
• Destructive interference (out of phase) lowers amplitude/loudness.
• Noise-canceling headphones use destructive interference.

Resonance

• Resonance occurs when vibrated at natural frequency.
• Natural frequency is where object vibrates easiest.
• Resonance amplifies sound.
• Resonance enhances sound in instruments.

Digital Audio

• Digital audio represents sound as numbers.
• Analog-to-digital conversion uses sampling and quantization.
• Sampling rate (Hz) is samples per second.
• Higher sampling rates give more accurate sound.
• Quantization assigns values to samples.
• Bit depth sets quantization levels for dynamic range/lower noise.