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BIEB 166 (26)
James Nieh (26)
Lecture 15

# BIEB 166 Lecture 15 (WI13)

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School
University of California - San Diego
Department
Biol/Ecology, Behavior, & Evol
Course
BIEB 166
Professor
James Nieh
Semester
Spring

Description
Lecture 15 Linearity of sound - Breakdown the complex sound in to simpler components - Sound is linear - Complex sound is a simple sum of its parts and different parts do not interfere or interact with each other ○ When two waves travel in opposite direction towards one another, they temporary add up, and then go the other way - This linearity makes analysis easier and it makes it possible for our ears to break sound down into its component frequencies Time domain - Temporal signal structure - How frequency and amplitude change over time - Time in the x-axis and amplitude in the y-axis 1. Amplitude modulation - How loud/soft the signal gets - In many cases, animals have evolved communication systems that are sensitive to temporal characteristics of the signal ○ How does the signal change with time Drosophila mating songs - The male is waving the wings around the female ○ The way he waves his wings creates a near-field sound - The ones that are closely related tends to have songs that are very similar ○ Pulses of sound: each pulse = 1 wave - All of these species have their very specific type of sound/amplitude modulation Frequency domain - Frequency structure of a signal - Frequency of a given moment of time 1. Frequency modulation - Same level of loudness, but frequency is changing up and down (high f /low f) - High frequency = shorter wavelength Low frequency = longer wavelength - Constant frequency, varying amplitude Constant amplitude, changing frequency How do we tease apart the frequency and temporal structure 1. Sound wave enter the ear 2. Ear drum is moving back and forth 3. Transmitted into the cochlear 4. Long membrane in the cochlear - When a specific frequency hits the cochlear (low/medium/high), the membrane separates the different frequencies - Mixed sound, different parts of the membrane are vibrating at the same time - Hair cell receptors that respond to the vibration and send signals to the brain Fourier Analysis - Frequency domain description - Any time domain signal can be broken down into a set of infinitely long sine waves ○ Any sound can be represented as the sum of sine waves of different relative amplitudes and phase displacements - This breakdown process is called Fourier Analysis Spectrum Spectrum - The spectrum of signal is a graphical representation of the frequencies in the signal and their relative amplitudes (amplitude is the strength of the signal) 1. The Frequency Spectrum - A graph of frequencies on the horizontal axis, and the amplitudes of each frequency component on the vertical axis - Different frequencies may have different amplitude in a certain moment - Set the lowest frequency as standard, and see how the other frequencies shifted relative to it (phase shift) ○ Shifted either upwards/downwards Be able to read the graphs 2. The Phase Spectrum - A graph of frequencies on the horizontal axis, and the relative phases of each frequency component which would have to
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