DOC PREVIEW
U of I CS 414 - Perception and Digital Audio

This preview shows page 1-2-24-25 out of 25 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 25 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 25 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 25 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 25 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 25 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

CS 414 – Multimedia Systems Design Lecture 2 –Auditory Perception and Digital AudioAdministrativeSlide 3Auditory PerceptionChanges in Air PressureAuditory SystemPhysical DimensionsSound Perception and PsychoacousticsPsychological DimensionsPsychological Dimensions (cont.)Sound IntensityDecibel ScaleDecibels of Everyday SoundsInterpretation of Decibel ScaleLoudness from Multiple SourcesExercisesLoudness and PitchFletcher-Munson ContoursMaskingFrequency MaskingSlide 21Slide 22Temporal MaskingSlide 24SummaryCS 414 - Spring 2011CS 414 – Multimedia Systems Design Lecture 2 –Auditory Perception and Digital AudioKlara NahrstedtSpring 2011CS 414 - Spring 2011Administrative Form Groups for MPs Deadline: Latest January 24 to email TA [email protected] 414 - Spring 2011Auditory PerceptionSound – physical phenomenon caused by vibration of material These vibrations trigger pressure wave fluctuations in the airWave formsCS 414 - Spring 2011Changes in Air PressureCS 414 - Spring 2011Auditory SystemEars, parts of brain, and neural pathwaysChanges in pressure move hair-like fibers within the inner earMovements result in electrical impulses sent to the brainPhysical DimensionsAmplitudeheight of a cyclerelates to loudnessWavelength (w)distance between peaksFrequency ( )cycles per secondrelates to pitch w = velocityMost sounds mix many frequencies & amplitudesSound is repetitive changesin air pressure over timeSound Perception and PsychoacousticsPsychoacousticsStudy correlation between physics of acoustical stimuli and hearing sensationsExperimental data and models are useful for audio codecModeling human hearing mechanismsAllows to reduce the data rate while keeping distortion from being audibleCS 414 - Spring 2011Psychological DimensionsLoudnesshigher amplitude results in louder soundsmeasured in decibels (db), 0 db represents hearing thresholdPitchhigher frequencies perceived as higher pitchHumans hear sounds in 20 Hz to 20,000 Hz rangeCS 414 - Spring 2011Psychological Dimensions (cont.)Timbre (tam-bre)complex patterns added to the lowest, or fundamental, frequency of a sound, referred to as spectraspectra enable us to distinguish musical instrumentsMultiples of fundamental frequency give musicMultiples of unrelated frequencies give noiseSound IntensityIntensity (I) of a wave is the rate at which sound energy flows through a unit area (A) perpendicular to the direction of travelP measured in watts (W), A measured in m2Threshold of hearing is at 10-12 W/m2Threshold of pain is at 1 W/m2APtEAI 1CS 414 - Spring 2011Decibel ScaleDescribes intensity relative to threshold of hearing based on multiples of 100log10IIdB CS 414 - Spring 2011I0 is reference level = 10-12 W/m2Decibels of Everyday SoundsSound DecibelsRustling leaves 10Whisper 30Ambient office noise 45Conversation 60Auto traffic 80Concert 120Jet motor 140 Spacecraft launch 180Interpretation of Decibel Scale 0 dB = threshold of hearing (TOH)10 dB = 10 times more intense than TOH20 dB = 100 times more intense than TOH30 dB = 1000 times more intense than TOHAn increase in 10 dB means that the intensity of the sound increases by a factor of 10If a sound is 10x times more intense than another, then it has a sound level that is 10*x more decibels than the less intense soundCS 414 - Spring 2011Loudness from Multiple SourcesUse energy combination equation where L1, L2, …, Ln are in dB)10...1010log(1010102101 LNLLL CS 414 - Spring 2011ExercisesShow that the threshold of hearing is at 0 dBShow that the threshold of pain is at 120 dBSuppose an electric fan produces an intensity of 40 dB. How many times more intense is the sound of a conversation if it produces an intensity of 60 dB?One guitar produces 45 dB while another produces 50 dB. What is the dB reading when both are played?If you double the physical intensity of a sound, how many more decibels is the resulting sound?CS 414 - Spring 2011Loudness and PitchMore sensitive to loudness at mid frequencies than at other frequenciesintermediate frequencies at [500hz, 5000hz]Human hearing frequencies at [20hz,20000hz]Perceived loudness of a sound changes based on frequency of that soundbasilar membrane reacts more to intermediate frequencies than other frequenciesCS 414 - Spring 2011Fletcher-Munson ContoursEach contour represents an equal perceived soundCS 414 - Spring 2011Perception sensitivity (loudness) is not linear across all frequencies and intensitiesMaskingPerception of one sound interferes with anotherFrequency maskingTemporal maskingCS 414 - Spring 2011Frequency MaskingLouder, lower frequency sounds tend to mask weaker, higher frequency soundsFrom http://www.cs.sfu.ca/CourseCentral/365/CS 414 - Spring 2011Frequency MaskingLouder, lower frequency sounds tend to mask weaker, higher frequency soundsCS 414 - Spring 2011Frequency MaskingLouder, lower frequency sounds tend to mask weaker, higher frequency soundsCS 414 - Spring 2011Temporal MaskingWhen exposed to a loud sound, the human ear contracts slightly to protect delicate structuresCauses louder sounds to overpower weaker sounds just before and just after itCS 414 - Spring 2011Temporal MaskingCS 414 - Spring 2011Summary Auditory Perception is very important for understanding digital audio representation Psychoacoustic is used in MP3 audio compression CS 414 - Spring


View Full Document

U of I CS 414 - Perception and Digital Audio

Documents in this Course
Lecture 1

Lecture 1

32 pages

LECTURE

LECTURE

30 pages

Load more
Download Perception and Digital Audio
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Perception and Digital Audio and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Perception and Digital Audio 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?