Image compression and video compression 2004 notes - 6 Audio compression

Image compression and video compression 2004 notes - 6 Audio compression

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1 Lecture notes of Image Compression and Video Compression series 6. Perceptual Audio Coding Prof. Amar Mukherjee Weifeng Sun #2 Topics z Introduction to Image Compression z Transform Coding z Subband Coding, Filter Banks z Introduction to Wavelet Transform z Wavelet Image Compression z Perceptual Audio Coding z Video Compression
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2 #3 Contents z Sound z Physiology of the Ear z Human Sound Perception z Psychoacoustics z Auditory Masking z Frequency masking z Temporal masking z MPEG Audio Compression z Example #4 z Many applications need digital audio z Storing z ipod z games z Streaming z Internet radio z Interactive multimedia session like VOIP, conferencing. z However, cannot apply entropy coder directly. z Very random, missing repeated sequence of byte pattern. Motivation
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3 #5 Sound z Sound is a continuous signal that is created by compressing and decompressing the air. z This changing air pressure causes the eardrum to vibrate. #6 Describing Sound z Intensity z Defined as power per unit area. z The level of perceived sound by a human is referred to as loudness . z Measured in terms of phons . z Defined as the perceive intensity at 1000 Hz by normal human population. z Pitch z frequency of sound (tone) z Quality (timbre)
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4 #7 Decibels z For most audio specifications, sound levels are presented in terms of decibels (dB), z A log scale for intensity changes. z The softest 1000 Hz tone heard by the normal ear is I 0 = 1 picowatt/meter 2 . z With I 0 as a reference, all other intensities, I , can be given in terms of dB by: #8 Physiology of the Ear z Thousands of “microphones” z hair cells in cochlea z Automatic gain control z muscles around transmission bones z Directivity z pinna z Boost of middle frequencies z auditory canal z Nonlinear processing z auditory nerve
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5 #9 The Outer Ear z For a point source of sound, it spreads out according to the inverse square law . z
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Image compression and video compression 2004 notes - 6 Audio compression

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