Properties of Sound - Lecture Notes

Vocabulary flashcards covering the key concepts from the Properties of Sound lecture notes, including audibility, wavelength, complex tones, harmonics, and analysis.

Audibility by Frequency

Study of which frequencies humans can hear and how sensitivity varies across the spectrum; the notes highlight speech-relevant frequencies with peak sensitivity around 500–6000 Hz.

Audible frequency range

The range of frequencies that listeners can hear; the notes emphasize sensitivity differences within this range and its importance for speech.

Speech sounds

Sounds that comprise human speech; the 500–6000 Hz region is particularly important for perceiving speech.

Wavelength

The distance one cycle of a sound wave occupies; symbolized by λ; related to speed of sound and frequency by λ = c/f.

Lambda (λ)

The Greek letter λ used to denote wavelength in acoustics.

λ = c/f

The fundamental relationship between wavelength, speed of sound (c), and frequency (f).

Speed of sound

The speed at which sound propagates through a medium; in air at room temperature it is about 343 meters per second.

Frequency

Number of cycles per second of a sound wave; measured in Hertz (Hz).

Low frequencies have longer wavelengths

As frequency decreases, wavelength increases; low frequencies produce longer wavelengths.

High frequencies have shorter wavelengths

As frequency increases, wavelength decreases; high frequencies produce shorter wavelengths.

Fundamental frequency (f0)

The lowest frequency of a periodic sound; the first harmonic (H1); common female F0 around 200 Hz.

Female voice example (λ from f0)

For f0 ≈ 200 Hz and c ≈ 343 m/s, λ = c/f ≈ 1.715 m, indicating the distance of one cycle in air.

Wavelengths for 250 Hz and 2000 Hz

250 Hz ≈ 1.37 m; 2000 Hz ≈ 0.17 m, illustrating how frequency and wavelength relate.

f = c/λ

An alternate form of the wavelength–frequency relationship used to compute frequency from a given wavelength.

Sine wave (pure tone)

A sound consisting of a single frequency with a sinusoidal waveform.

Complex tones

Sounds composed of two or more waves with different frequencies.

Periodic complex tones

Complex tones whose vibration pattern repeats exactly over time.

Aperiodic complex tones

Complex tones with non-repeating, random patterns; often with no periodic repetition.

Harmonics

In periodic complex tones, frequencies that are integer multiples of the fundamental frequency (H1).

First harmonic (H1) / f0

The fundamental frequency; H1 equals f0, the lowest component of a periodic tone.

Harmonics relationship (Hn = n × H1)

Higher harmonics are integer multiples of the fundamental frequency; e.g., H2 = 2×H1, H3 = 3×H1, etc.

Example harmonic frequencies (H1 = 100 Hz)

H2 = 200 Hz, H3 = 300 Hz, H4 = 400 Hz, illustrating the harmonic series.

Spectrum

A plot with frequency on the x-axis and amplitude on the y-axis showing the frequency content at a given moment; a single time slice.

Fourier analysis (FFT)

A method to decompose a complex tone into its frequency components; the spectrum is obtained via Fourier analysis.

Aperiodic complex signals (white noise)

Signals with multiple frequencies not harmonically related, no repetitive pattern; white noise has infinite frequencies, random phases, and flat amplitude across frequencies.

Minimum Audibility Curve

Graph showing the threshold of hearing across frequencies, indicating the minimum sound pressure level detectable at each frequency.