Glossary

“Ambient Music must be able to accommodate many levels of listening attention without enforcing one in particular . . . .”

Ambient Music
According to the Miriam Webster Dictionary, Ambience is a feeling or mood associated with a particular place, person, or thing. The form of music that has been developed to enhance spaces fits into a category called Ambient Music. “Ambient Music must be able to accommodate many levels of listening attention without enforcing one in particular . . . .” — Brian Eno. Ambient Music has a spaciousness to the overall sound field that allows each note to fully evolve and resolve.

— Brian Eno

Amplitude
Scientifically speaking, amplitude is the maximum extent of an oscillation measured from the point of equilibrium of a particle within the medium of transmission. It has a direct effect on volume, measured in decibels, and can be thought of as the height of a wave measured against the midpoint. The amplitude of a sound wave relates to the energy carried through the medium such as air. Volume is a perceptual sound phenomenon, experienced as intensity.

Entrainment
The tendency of two oscillating bodies to synchronize movement and timing, i.e. pendulum clocks on the same wall will synchronize. Choirs singing together will synchronize breath and heartbeat to the rhythm of the music. Both anecdotal experience and music therapy research show that biological rhythms controlled by the autonomic nervous system will entrain to external beats, foot tapping to music being the most obvious example.

Frequency Measured in Hertz
Frequency is measured in Hertz, Hz. It can be visualized as the number of waves to pass a given point in space per second. So 20 Hz is 20 waves per second. Lower frequencies generate fewer wave cycles per second, and we perceive these as lower pitch or bass sounds. Higher frequencies generate more wave cycles per second, and we perceive these as higher pitch sounds.

Harmonics
Very few sounds that we hear in the natural world are pure tones. Tuning forks and oscillators generate pure tones, usually for calibration purposes. In music sounds have complex tapestries of secondary oscillations that are mathematically related to the root tone. Using the example of a C note, when played on a piano, the C string an octave above will vibrate in sympathy, the G above that, the C above that, the E and G on through a theoretically infinite series (called the harmonic series). Harmonics are sometimes called overtones or partials.

Hertz
Named for Heinrich Hertz (1857-1894), a “hertz” is a unit of measurement used to measure wave forms. One Hertz Hz is one cycle per second - measuring a wave, trough to trough or crest to crest. The number of cycles per second is called Frequency. For example, the frequency of the A note above middle C on the piano tuned to concert pitch is 440 Hertz.

Masking
Masking happens when distinct sounds overlap frequencies, one sound momentarily masking the other. Masking has an important function in noise reduction. Music with suitable arrangements of drones and bass in the lower midrange or white noise generators work on the principal of masking. Masking provides a layer of sound that submerges or masks the effects of environmental sounds, such as conversations down the hall or road noise.

Noise
There are 5 degrees of noise: white, pink, brown, blue, and green, and each have ramifications and uses in music for therapy. White noise has equal intensity across all sound spectrums, while pink noise has less intensity in the higher frequencies and is experienced as more soothing. Brown noise has significantly lower frequency content, such as thunder rumbling, and blue noise is higher frequency, a hissing sound, and can experienced as more of an irritant.

  • White-all frequencies equally

  • Pink-upper mid range accentuated, some elements of tone

  • Brown-predominantly lower midrange, the most research on sleep and the relaxation response has been done with brown noise

  • Green-sound centered around 500 Hz, nature sounds, water, and birdsong

Polyrhythm
In music a polyrhythm is a rhythmic pattern that combines two or more distinct and different rhythms simultaneously. In music when two or more rhythms are overlain in a drum sequence, the mind is involved in seeking a deeper order. For instance, if a beat of 4/4 and 6/4 are overlain, the rhythms will align every 12th beat. Polyrhythms are commonly found in African drumming. The mind can find multiple patterns within a polyrhythm, choosing to align with individual parts or finding a deeper order that underlies the beat pattern.

The concept of poly (multiple) rhythms can be extrapolated beyond music to encompass human physiology, where biorhythms such as heartbeat, respiration, craniosacral pulse, digestive cycles, reproductive cycles, and sleep cycles all function as an integrated polyrhythm that is synchronized in a wellness state and disrupted in a diseased state.

Psychoacoustics
Psychoacoustics is the study of sound perception, the subjective experience of sound and music. An example of a psychoacoustic effect often used in small speaker design is the ability of the human mind to anticipate and project a bass sound derived from harmonic information when the speaker is not physically capable of reproducing the lower note. Another common psychoacoustic effect is called masking. Masking happens when distinct sounds overlap frequencies and one sound is momentarily masked by the other. Sound location is a psychoacoustic effect we utilize daily. We have two ears, which allows us to auto locate sounds.

Resonance
Resonance literally means to re-sound. When waves are generated in a resonant space they will refract on surfaces, such as walls, floor, and ceiling and recombine in space, creating a reverberation effect that deepens and sustains the sound. Another effect of resonance is called the resonance frequency, a phenomenon that occurs when an external vibration occurs at a frequency that matches the frequency of a room or structure causing a self-sustaining resonance that builds exponentially. The most famous example is the opera singer hitting the note that is the resonance frequency of a crystal glass, causing the glass to vibrate so intensely it shatters.

Relaxation Response
Relaxation Response is a term coined by Dr. Herbert Benson of Harvard Medical School. Dr Benson and his associates pioneered research using meditation and recorded the effects, such as reduced metabolism, rate of breathing, heart rate, and brain activity. Dr. Benson labeled these changes the “relaxation response.” The relaxation response is the foundation of Mind Body Medicine, and recent neurological music therapy research shows music’s efficacy in inducing a relaxation response.

Sound Waves
Changes in air pressure are generated by the movement of energy. This creates patterns of disturbance that propagate out from a vibrating source, such as a guitar string. The disturbances travel as oscillating waves through a medium, for instance air or water. The particles of the medium carry the sound wave, reminiscent of the wave at a football game, the fans standing as the wave passes but not changing seats. Technically speaking, sound cannot exist in a vacuum because a vacuum does not contain a medium.

Tempo
Tempo is the speed at which music is played, measured in beats per minute (bpm). Tempo has been shown to affect metabolic entrainment, and music therapy research shows slower tempo in the 60bpm range can facilitate a relaxation response, while a faster 120bpm would be more stimulative.

Timbre
The relative strength of the harmonics that sound with a root note determines the timbre or character of a sound. For instance, a flute and a clarinet playing the same note do not sound the same. This difference is the quality of timbre. In the case of a flute, the harmonics are predominantly evenly ordered, that is, in the key of C the strongest overtones are the octaves. A clarinet has only odd ordered harmonics, so the strongest overtones are the 3rd harmonic, G, and the 5th harmonic, E, giving us the distinctive timbre of a clarinet.

Waveform
According to Merriam Webster, “a waveform is usually a graphic representation of the shape of a wave that indicates its characteristics (such as frequency and amplitude).” The shape of a waveform determines its sound. The most common simple waveform is a sine wave, which has an even curve from crest to trough to crest. Other examples of waveforms used in sound synthesis are sawtooth, square, triangle, and pulse. These waveforms have distinctive sounds and psychoacoustic effects.

Wavelength
The length of a wave as measured from trough to trough or crest to crest. Lower frequency waves have a longer wavelength. 20 Hz, the lower threshold of hearing, has a wavelength of around 60 feet. The wavelength of the upper threshold of hearing, 20,000 Hz, is about .7 of an inch.