Biology Reference
In-Depth Information
Fluctuation strength describes the sensation caused by relatively slow amplitude
modulation within auditory filters with a maximum sensitivity at 4 Hz.
The unit of fluctuation strength is the vacil , referenced to 60 dB 1-kHz pure tone
100 % amplitude modulated at 4 Hz.
Pitch is defined as that auditory attribute of sound according to which sounds can be
ordered on a scale from low to high . To date this definition still is a useful basis,
although it must be complemented by considering certain additional aspects.
For instance, in a first experiment (Gygi et al. 2007 ) 145 sounds were rated in
20 semantic dimensions, and the rating suggests that 90 % of variance was
associated with four factors: harshness, size, complexity, and appeal. In a second
experiment the sounds were submitted to a low- and high-pass filter to understand
what spectral region was selected in the sound identification of a set of 70 environ-
mental sounds (Table 5.2 ) using limited spectral regions(Gygi et al. 2004 ). Subjects
were able to identify sounds also when they were severely filtered (70 % or more of
correct identification). The spectral region requested for identification ranges from
1,200 to 2,400 Hz, similar to the spectrum related to speech recognition. This type
of approach investigates the minimum code for sonic identification.
A psychological space or a cognitive template probably is when an acoustic
stimulus is captured by our hearing system and processed in our brain. The
minimum structure sound probably increases the speed and the efficiency of the
identification. A three-dimensional multidimensional scaling (MDS), a set of
related statistical techniques often used in information ordination, was adopted to
identify similarity in sounds and to reduce the high-dimensional acoustic space to
few perceptual dimensions.
People perceived sounds by attributing categories according to the acoustic
features of those sounds, including harmonicity, spectral spread, continuity, peri-
odicity, and envelope modulation. An MDS approach can create similarity between
the different types of sources, for instance, vocalizations, impacts, and water
sounds.
Birds and waterfalls are considered pleasant sounds but technological sounds are
associated with negative feelings of a site. Children at play and talking people are
considered positive. To discover the relationship between these psychoacoustic
processes and the physical composition of a soundscape remains an important
research issue. Axelsson et al. ( 2010 ) have utilized 50 binaural soundscape excerpts
of 30 s in duration selected from a large set of urban recordings in London and
Stockholm among a great variability of soundscapes and sound events with a broad
range of sound pressure level (43-79 dB L Aeq, 30s ) (Fig. 5.5 ). These 50 excerpts
were from ten kinds of location: urban courtyard, motorways, pedestrian street,
school yards, suburban parks, suburban recreational areas, suburban residential
areas, urban parks, urban square market, urban street.
The technological sounds were from airplanes, individual cars, motorcycles,
road traffic, car alarms, car horns, chainsaw, rock drill, street sweeper, construction
work, train ventilation fans, and sirens of emergency vehicles.
Search WWH ::




Custom Search