PSY247 Lecture Notes - Lecture 2: Interaural Time Difference, Monaural, Oval Window
4 Jun 2018
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Audition
Sound and sound waves
Sound
- Sound is a pressure wave, which is carried through the air
at 335m/second.
- Sound is a representation of periodic repetitions of
compression and rarefaction. Sound waves
- At rest, air molecules are constant and can be represented
as equally spread dots on a graph.
- When vibrations occur, the molecules compress (top of the
wave) and then refract (bottom of the wave). Properties of a
sound wave
- A sine wave is a pure tone of a single frequency.
- Soundwaves have 3 features or parameters:
o Frequency, which is perceived as the pitch. This is measured in full
waves per
second and is described in Hz.o Amplitude, which is perceived as
loudness. This is measured by the height of the
wave from peak to trough and is described in dB.▪ dBs are
logarithmic, which means that equal ratios of pressure correspond to
equal increments in dB level.▪ 10x increase in pressure =
20dB.▪ 2x increase in pressure = 6dB.▪ Conversations are
approximately 60dB.
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o Phase, which is perceived as timbre. This is measured by the angle
of the wave at a given point in time and is described in degrees.
Adding sound waves together
- This is done through the process of Fourier synthesis.o
In contrast, Fourier analysis is the process in which waves can be
separated.
- As sound waves are linear, they can be added together
logically, which is sometimes referred to as linear summation.
- When adding two of the same soundwaves, amplitude
increases, but not frequency.
- When adding two different sound waves, both amplitude
and frequency change.
- A waveform that represents a sound is the sum of each of
the sine waves with different frequencies, amplitudes and phases.
Complex sounds
- Waveforms are periodic and therefore the x-axis (time)
provides little information.
- For this reason, spectrums are normally plotted, with
frequency (x) vs. amplitude (y), or frequency (x) vs. phase (y).
This spectrum looks like a scatter plot.
- The component/wave with the lowest frequency is called
the fundamental frequency.
- An attack is the complex harmonic amplitude at the start
of a note.
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10
Fourier analysis
- This is the decomposition of a complex sound into its
component frequencies.
- Once sound waves are broken down, a fundamental
frequency (lowest frequency and characteristic pitch) and
harmonics (remainder of the frequencies) result. o Harmonics are
numbered in order of distance from the fundamental.
- The application of Fourier theory/analysis relies on linear
systems theory, which suggests that the filter is linear and meets
the following assumptions
o Output mustn’t contain a frequency that isn’t present in input.o If
amplitude of input is changed by some factor, then the output must also
change. o The output of the combination of each wave should be equal
to the output of each
wave if processed separately but at the same time.- Note: the head
removes higher frequencies when sound passes to the ear furthest from
the
source.
Is the ear a Fourier analyser?
Yes No
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Document Summary
Sound is a pressure wave, which is carried through the air at 335m/second. Sound is a representation of periodic repetitions of compression and rarefaction. At rest, air molecules are constant and can be represented as equally spread dots on a graph. When vibrations occur, the molecules compress (top of the wave) and then refract (bottom of the wave). A sine wave is a pure tone of a single frequency. Soundwaves have 3 features or parameters: frequency, which is perceived as the pitch. This is measured in full waves per second and is described in hz. o amplitude, which is perceived as loudness. This is measured by the height of the wave from peak to trough and is described in db. Dbs are logarithmic, which means that equal ratios of pressure correspond to equal increments in db level. Conversations are approximately 60db: phase, which is perceived as timbre.
