SOUND – ENVIRONMENT INTERACTION
Source: http://www.sfu.ca/sonic-studio/handbook/index.html
Barry Truax, editor, Second Edition, 1999. Originally published by the World Soundscape Project, Simon Fraser University, and ARC Publications, 1978.
SOUNDSCAPE STUDIES: one aspect of soundscape studies is the notation of spatial environments, called “sonography”, by analogy to “geography”. All sounds can be heard over a certain space, thus each has a “profile”; each listener can hear sounds from varying distances, thus each location has an “acoustic horizon”.
ACOUSTIC HORIZON
The farthest distance in every direction from which sounds may be heard. Incoming sounds from distant sources define the outer limits over which acoustic communication may normally occur, and thus help to define the perceived geographical relationships between communities.
SOUND SIGNALs from one community, for instance, may penetrate others. The importance of their signalling function usually diminishes, but they also act as a reminder of the various ways in which the separate communities are related. In some communities, a change in the perceived acoustic horizon, such as when a certain bell or other distant sound is particularly noticeable, has a predictable meaning as a weather forecast.
Since the definition of an acoustic horizon depends on the perception of quiet sounds, it is highly susceptible to change by SOUND INTRUSIONs and other MASKing sounds. These reduce the distance of what can be heard, a characteristic shrinkage that runs parallel to that of the acoustic profile of sound signals with the rising AMBIENT NOISE of communities (see ACOUSTIC SPACE, LO-FI). Acoustic links between communities and parts of communities are now often replaced by ELECTROACOUSTIC and media links.
SONOGRAPHY
The art of SOUNDSCAPE notation. It includes customary methods of notation such as the SPECTROGRAM and the graphic LEVEL RECORDER, but beyond these it also attempts to register the geographic distribution of sound events. Various mapping techniques are employed to create, for instance, the ISOBEL contour map and the ACOUSTIC PROFILE.
Sonography is an alternative term for ultrasound scanning.
ULTRASONIC – Sound at frequencies above the audible range, namely above 20 kHz, audible only to various non-human species. Because of its very short WAVELENGTH in the megahertz range, ultrasound is used as a safe alternative to X-ray photography in medical diagnosis. Ultrasound scanning is sometimes called sonography. SUPERSONIC was once used in acoustics synonymously with ultrasonic, but the former is now associated exclusively with speeds higher than that of sound.
SPECTOGRAM – A SOUND ANALYSER with graphic output showing the SPECTRUM or frequency content of a sound and its variation in time. It is commonly used for speech analysis, and is sometimes called a sonagraph or visible speech. The graphic output is called a spectrogram or sonagram.
ISOBEL CONTOUR MAP – Equal SOUND PRESSURE LEVEL (SPL). Locations where equal SPL readings are taken, or for which they are extrapolated from other readings, may be joined together in isobel contour lines, similar to the geographer’s equal altitude contours.
An isobel map shows variations in sound pressure over a given area by connecting those points for which the measured levels are equal.
SOUND PRESSURE LEVEL (SPL) – The term most often used in measuring the magnitude of sound. It is a relative quantity in that it is the ratio between the actual SOUND PRESSURE and a fixed reference pressure. This reference pressure is usually that of the THRESHOLD OF HEARING which has been internationally agreed upon as having the value .0002 dynes/cm2.
ACOUSTIC SPACE
SOURCE – http://www.sfu.ca/sonic-studio/handbook/Acoustic_Space.html
The perceived area encompassed by a SOUNDSCAPE, either an actual environment, or an imagined one such as produced with a tape recording and several loudspeakers. Every sound brings with it information about the space in which it occurs (for environmental sound) or is thought to occur (as with synthesized sound).
With environmental sound, LOUDNESS and the quality of REVERBERATION mainly determine the kind of space that is perceived, enclosed or open, large or small (see DIFFUSE SOUND FIELD, FREE FIELD). The sense of speeding motion is usually perceived by the presence of a DOPPLER EFFECT.
See: AZIMUTH, BINAURAL HEARING, PROJICIENCE, STEREOACUSIS. See also: BINAURAL RECORDING, DIFFUSION, KUNSTKOPF, QUADRAPHONIC, SOUND EFFECT, STEREOPHONIC.
A HI-FI environment, in which all sounds may be heard clearly, is characterized by a well defined sense of acoustic space in that all sounds may be perceived as occurring in the direction and at the distance where they originate. In such an environment, one can easily orient oneself with respect to these sounds. On the other hand, in a LO-FI environment, sounds are crowded together, obliterating all sense of unique space, and creating a claustrophobic effect on the individual. Compare: SIGNAL-TO-NOISE RATIO.
Acoustic space may also refer to the profile of a sound or SOUND SIGNAL over its surrounding environment. The acoustic space of any sound is that area over which it may be heard before it drops below the level of AMBIENT NOISE. The diagram below shows the area over which the bells of the Holy Rosary Cathedral in Vancouver may be heard, a profile greatly diminished from the early 20th century when they could be heard for several miles.
SOUNDSCAPE – An environment of SOUND (or sonic environment) with emphasis on the way it is perceived and understood by the individual, or by a society. It thus depends on the relationship between the individual and any such environment. The term may refer to actual environments, or to abstract constructions such as musical compositions and tape montages, particularly when considered as an artificial environment. The study of the systematic relationships between humans and sonic environments is called SOUNDSCAPE ECOLOGY, whereas the creation, improvement or modelling of any such environment is a matter of SOUNDSCAPE DESIGN.
LOUDNESS – The subjective impression of the intensity or magnitude of a sound. It is dependent on FREQUENCY, WAVEFORM and duration, as well as SOUND INTENSITY or SOUND PRESSURE. It is expressed quantitatively in units of SONEs and PHONs for SINE TONEs or narrow band noise, and in terms of PERCEIVED NOISE LEVEL (PNdB) for broad band environmental sounds.
REVERBERATION – Reverberation is a result of multiple REFLECTIONs. A SOUND WAVE in an enclosed or semi-enclosed environment will be broken up as it is bounced back and forth among the reflecting surfaces. Reverberation is, in effect, a multiplicity of ECHOes whose speed of repetition is too quick for them to be perceived as separate from one another. W.C. Sabine established the official period of reverberation as the time required by a sound in a space to decrease to one-millionth of its original strength (i.e. for its intensity level to change by -60 dB).
DIFFUSED SOUND FIELD – A space with many reflecting surfaces and small sound ABSORPTION. Repeated REFLECTIONs and DIFFRACTIONs of sound within a space result in good DIFFUSION and a uniform distribution of sound energy. A diffuse sound field is typically created in gymnasia, swimming pools and interior spaces with marble, concrete or glass walls, but it also can occur outdoors with sounds coming from many directions, such as in urban streets lined with high-rise buildings.
DOPPLER EFFECT – The change in PITCH of a sound heard by a listener when the source and observer are in relative motion to each other. As the observer and sound source come together, the perceived pitch is higher than that of the source when stationary, and as they move apart it is lower. The change in pitch is a function of the difference in relative velocity of observer and source. As the source and observer move closer, the sound waves may be thought of as being compressed together, and therefore, because the WAVELENGTH decreases, the apparent pitch rises. Similarly, as the source and observer move apart, the waves are expanded and the increased wavelength corresponds to a drop in pitch.
HI-FI – Abbr. for high-FIDELITY, that is, a system reproducing a full audio frequency SPECTRUM (20 to 20,000 Hz) and a favourable SIGNAL-TO-NOISE RATIO. The most general use of the term is in ELECTROACOUSTICs, such as when applied to an AMPLIFIER or a recording. In terms of SOUNDSCAPE studies, the hi-fi environment is one where all sounds may be heard clearly without being crowded or MASKed by other sounds and NOISE.
LO-FI – Abbr. for low-FIDELITY, that is, a system which reproduces less than a full frequency SPECTRUM, and which has a poor SIGNAL-TO-NOISE RATIO. The most general use of the term is in ELECTROACOUSTICs, such as when applied to an AMPLIFIER or recording. See SCHIZOPHONIA for sound examples. In terms of SOUNDSCAPE studies, the lo-fi environment is one in which signals are overcrowded, resulting in MASKing and lack of clarity.
SCHIZOPHONIA – (Greek: schizo = split; phone = voice, sound) The term was first employed by R.M. Schafer in The New Soundscape (Toronto, 1969, pp. 43-47) to refer to the split between an original sound and its ELECTROACOUSTIC reproduction in a SOUNDSCAPE.
Original sounds are tied to the mechanisms which produce them. Electroacoustic sounds are copies and they may be reproduced at other times or places. Schafer employs this ‘nervous’ word in order to dramatize the aberrational effect of this twentieth century development.
SIGNAL TO NOISE RATIO (SNR) – The ratio of the magnitude of the wanted SIGNAL to that of the unwanted NOISE, expressed as a simple arithmetic ratio or in DECIBELs. For example, the ratio between the input signal and the system noise of an amplifier. Also abbreviated S/N.
A signal-to-noise ratio is said to be favorable when the signal predominates; that is, it can be clearly distinguished from the noise, and exceeds it by at least 60 dB. When signal and noise are less clearly distinguishable, the signal-to-noise ratio is said to be poor or low.
SOUND SIGNAL - Compared to NOISE, which traditionally is thought of as unwanted sound, a SIGNAL is any sound or message which is meant to be listened to, measured or stored. In SOUNDSCAPE studies, sound signals are always treated in relation to their AMBIENT or KEYNOTE context, since they complement that context in the same way figure and ground are related in visual perception. Thus, a study of signals also reveals important information about the overall sound environment. The increase in the level of emergency warning signals during this century, for instance, has been closely proportional to the increase in the AMBIENT NOISE LEVEL of cities.
KEYNOTE (SOUND) - In music, keynote identifies the key or tonality of a particular composition. It provides the fundamental tone around which the composition may modulate but from which other tonalities take on a special relationship. In SOUNDSCAPE studies, keynote sounds are those which are heard by a particular society continuously or frequently enough to form a background against which other sounds are perceived. Examples might be the sound of the sea for a maritime community or the sound of the internal combustion engine or HUMs in the modern city. Often keynote sounds are not consciously perceived, but they act as conditioning agents in the perception of other SOUND SlGNALs. They have accordingly been likened to the ground in the figure-ground relationship of visual perception.
AMBIENT NOISE – The background sound of an environment in relation to which all foreground sounds are heard, such as the ‘SILENCE’ of an empty room, conversation in a restaurant, or the stillness of a forest. Ambience is actually comprised of many small sounds, near and far, which generally are heard as a composite, not individually.