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The sound
is a longitudinal wave, namely the shift of the airwave is in the direction of
propagation of the wave. In the air the sound spreads from the vibration and
the oscillation of the molecules of air. From a source that oscillates some air
molecules generate periodic pressure differences, which spread through the
environment, creating sound waves. The human ear responds to these pressure
differences.
The notes
are sounds at fixed frequencies (fundamental), which when combined properly
leave to human ear a pleasant auditory sense. The musical notes are classified
in octaves, which are repeated. Two successive octaves include the same notes
at twice their fundamental frequencies. In an octave distinguish seven different
notes. The nomenclature has prevailed globally assigns the first seven letters
of the Latin alphabet in seven basic notes: A, B, C, D, E, F, G. At the same
time is used the Latin nomenclature too which is respectively: la, si, do, re,
mi, fa, sol. Furthermore, mostly used a number in the name of the note, which
indicates in which octave the note belongs. Among some of the seven basic notes
exists some more notes, identified as the hash key and designated by adding the
# symbol in the name of the basic note. The series of notes finally formed by
the following steps: A, A #, B, C, C #, D, D #, E, F, F #, G, G #. The change
from one step to another is called semitone, while two successive semitones
constitute a tone. The relationship between the fundamental frequencies of two
consecutive semitones given by the expression:
As a
characteristic note, the basis of regulating most musical instrument is the A4
with frequency 440Hz. The figure below shows the diagram of the notes used in
music. The horizontal axis shows the notes and the vertical axis the frequency
in logarithmic scale.
When a note
is produced by any musical instrument, the resulting sound wave contains the
fundamental frequency and also multiples of it called harmonics. Each
instrument has its own characteristic sound, so we can distinguish it from
other instruments and recognize it. This feature is called timbre or tone of
the instrument and depends on the harmonics the instrument can produce and the
intensity of each shaping in the final sound. So it is possible to determine
the frequency spectrum for each instrument and reflected in the chart. The figure
below shows the frequency spectrum of the violin which distinguished the first ten
harmonics. The first harmonic (1) is the fundamental frequency and the
remaining harmonics (2-10) is derived first to ninth frequencies (overtones 1st
to 9th).
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