Acoustics.docx

Acoustics MUS 132 Unit 1

Harmonic Spectrum •  Has partials that integral multiples of a single, fundamental frequency. Partials also called overtones. A harmonic (or a harmonic partial) is any of a set of partials that are whole number multiples of a common fundamental frequency. •  This set includes the fundamental, which is a whole number multiple of itself (1 times itself). Other pitched instruments, especially certain percussion instruments, such as marimba, vibraphone, tubular bells, and timpani, contain mostly inharmonic partials, yet may give the ear a good sense of pitch. Unpitched, or indefinite-pitched instruments, such as cymbals, gongs, or tam-tams make sounds (produce spectra) rich in inharmonic partials

Harmonic Spectrum – Musical/Physical

Inharmonic Spectrum •  The description of the timbre of a complex sound such as a gong. Its partials are not integral multiples of a single fundamental. Examples are cymbals, xylophone, and chimes.

Frequency •  The number of repetitions of a waveform in a given unit of time. The number of cycles per unit of time is called the frequency. •  For convenience, frequency is most often measured in cycles per second (cps) or the interchangeable Hertz (Hz) (60 cps = 60 Hz), named after the 19th C. physicist. 1000 Hz is often referred to as 1 kHz (kilohertz) or simply '1k' in studio parlance. The hertz is named after the German physicist Heinrich Hertz (1857– 1894),

Hertz •  Unit for measuring frequency in cycles per second.

Frequency

Amplitude •  The objective measurement of the degree of change (positive or negative) in atmospheric pressure (the compression and rarefaction of air molecules) caused by sound waves. Sounds with greater amplitude will produce greater changes in atmospheric pressure from high pressure to low pressure. Amplitude is almost always a comparative measurement, since at the lowest-amplitude end (silence), some air molecules are always in motion and at the highest end, the amount of compression and rarefaction though finite, is extreme. In electronic circuits, amplitude may be increased by expanding the degree of change in an oscillating electrical current. A woodwind player may increase the amplitude of their sound by providing greater force in the air column i.e. blowing harder.

Amplitude

Timbre •  The parameter of sound associated with waveshape. In simple terms, timbre is what makes a particular musical sound different from another, even when they have the same pitch and loudness. In psychoacoustics it is referred to as tone color or tone quality. What other words can be used to describe the sound besides just the instrument. Play instruments and ask for descriptions.

Decibel •  A commonly used unit of sound-level measurement. The decibel (dB) is a logarithmic unit used to express the ratio between two values of a physical quantity, often power or intensity. One of these quantities is often a reference value, and in this case the decibel can be used to express the absolute level of the physical quantity. The number of decibels is ten times the logarithm to base 10 of the ratio of the two power quantities.[1] One decibel is one tenth of one bel. The bel is named in honor of Alexander Graham Bell, but is seldom used.

Cent •  Cent: 1/100th of a semitone. The cent is a logarithmic unit of measure used for musical intervals. Twelve-tone equal temperament divides the octave into 12 semitones of 100 cents each. Typically, cents are used to measure extremely small finite intervals, or to compare the sizes of comparable intervals in different tuning systems, and in fact the interval of one cent is much too small to be heard between successive notes.

Unison •  The interval described by two pitches with the same fundamental. Unison or perfect unison (also called a prime, or perfect prime[3]) may refer to the (pseudo-)interval formed by a tone and its duplication (in German, Unisono, Einklang, or Prime), for example C–C, as differentiated from the second, C–D, etc. In the unison the two pitches have the ratio of 1:1 or 0 half steps and zero cents. Although two tones in unison are considered to be the same pitch, they are still perceivable as coming from separate sources, whether played on instruments of a different type

Octave •  A pitch interval that can be represented with a frequency ratio of 2:1. In physical terms, an interval is the ratio between two sonic frequencies. For example, any two notes an octave apart have a frequency ratio of 2:1. This means that successive increments of pitch by the same interval result in an exponential increase of frequency, even though the human ear perceives this as a linear increase in pitch. For this reason, intervals are often measured in cents, a unit derived from the logarithm of the frequency ratio. The size of an interval between two notes may be measured by the ratio of their frequencies.

Phase •  The relative displacement in time between the starting points of two or more waveforms of the same frequency. Phase denotes a particular point in the cycle of a waveform, measured as an angle in degrees. It is normally not an audible characteristic of a single wave (but can be when we use very low-frequency waves as controls in synthesis). Phase is a very important factor in the interaction of one wave with another, either acoustically or electronically

Basic Waveform Spectra Sine Wave •  Most basic possible waveform. It contains only one partial, the fundamental. Characteristic is that of en eerie tone. Triangle Wave •  It sounds (and looks) a bit like the sine wave but has some hollow-sounding quiet overtones. It is made up of only odd numbered harmonics : F, 3F, 5F, 7F 9F etc. The amplitudes of the harmonic series decreases exponentially. Square Wave •  It has very sharp corners, has a hollow sound with quite strong overtones. It is made up of only odd numbered harmonics : F, 3F, 5F, 7F, 9F etc. The amplitudes of harmonic series decreases steadily. Sawtooth Wave •  is available as RampUp or RampDown (which sound the same). It has a very bright and rich sound with strong overtones. It is made up of all harmonics : F, 2F, 3F, 4F, 5F,6F etc. The ampitudes of harmonic series decreases steadily.

Noise Spectra Noise: •  Does not have a harmonic spectrum or distinct partials

White Noise •  Does not have a harmonic spectrum or distinct partials. Equal energy among all frequencies (frequency bands). 100 Hz to 200 Hz…

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Pink Noise •  Has equal energy per octave. Contains the same amount of energy per musical octave, therefore the quality of a more bass heavy sound.

Human Hearing Range The human hearing range is between 20 Hz and 20,000 Hz (20 KHz). This narrows with time and amount of exposure to sound. There are 10 octaves in the human auditory range.

Octaves in the human hearing range. •  20 – 40 Hz •  40 – 80 Hz •  80 – 160 Hz •  160 – 320 Hz •  320 – 640 Hz •  640 – 1.28 KHz •  1.28 – 2.56 KHz •  2.56 – 5.12 KHz •  5.12 – 10.54 KHz •  10.24 KHz to top of range