Prof. Greg Francis1PSY 310: Sensory and Perceptual ProcessesPurdue UniversitySound QualityPSY 310Greg FrancisLecture 32Name that tune!Purdue UniversitySound perception An integral part of our modern world Billions are spent annually on Creation of new sounds or sound sequences (music) Equipment to play sounds (iPods, speakers, stereosystems, surround sound theater systems) Buildings to present sounds (opera houses, symphonyhalls, recording studios) People who are gifted with sound (singers, musicians,song writers) This is true all over the world Much of the emphasis is to get quality sound But what does this mean?Purdue UniversityQuality terms For stereo systems, many terms used to describe quality have todo with the frequencies of sound that are generated and/or thelocation of sounds A system cannot produce all frequencies equally well Here’s some common terms for stereo speakers and what theymean Forward (Recessed): vocals, male and female, tend to be verypresent (absent), located in front (behind) the speakers Spacious, airy, open: the sense of space present around theinstruments and singers Closed, muted, dry: indicate the midrange and treblefrequencies are rolled off or depressed and dull Rich: full, rounded sound with lots of deep, sonorous bassPurdue UniversityQuality terms Sibilant: the speaker has a midrange/treble peak thatemphasizes the "sss" and "ttt" sounds of singers’ vocals Strident: way too much treble output, making brass and stringsound shrill or harsh Thin: means the speaker has little or no bass output Boomy: has too much bass that dominates its sound Punchy: powerful upper bass, like a disco, but no really deepbass Muddy: the midrange isn’t clear; that it’s hard to separate thedistinct contributions of male and female singers in a chorus Suck-out: valley or other uneven response in mid-rangefrequencies Nasal: what a midrange peak does to vocals, like what happensto your voice when you cup your hands around your mouth whileyou’re speaking.Purdue UniversityMusic We already noted that different instruments sounddifferent in large part because they include sounds offrequencies other than the “main” sound In addition, notes on an instrument include: Attack: the buildup of sound at the beginning of the tone Decay: the decrease in sound at the end of a tone We are very sensitive to these aspects of sound, even ifwe don’t know what we are sensitive to Johann Sebastian Bach. The Well-Tempered Clavier, Book 1,Prelude 1 (in C major) Demonstration of pianoPurdue UniversityArchitectural acoustics Rooms where sound is very important must be designed topromote quality sound Need to avoid echo and problem reverberations It’s a difficult problem, and expensive to repair Often start with a model (1:50 scale) Present sounds of different frequencies and measure the sound atdifferent places in the modelProf. Greg Francis2PSY 310: Sensory and Perceptual ProcessesPurdue UniversityArchitectural acoustics A sound (like a gunshot) at the stage hasmultiple effectsPurdue UniversityArchitectural acoustics An acoustical engineer can identify which part ofthe hall contributes to different reverberations andintroduce new elements to stop echoPurdue UniversityArchitectural acoustics You want somereverberation,else the soundseems “flat” Different parts ofthe hallcontribute to thereverberationsPurdue UniversityArchitectural acoustics The models canmatch theactual structurequite wellPurdue UniversityAuditory grouping We noted that sounds all come together on the basilarmembrane How do we track one sound stream? Similar to the issue faced by visual grouping Gestalt laws Auditory stream segregation Identification of different perceptual streams of sounds Location: sounds from the same place, come from the samesource Similarity of timbre (complex sound): sounds of similar timbrecome from the same source Similarity of pitch (Pitch demo): similar pitches come from thesame sourcePurdue UniversityAuditory grouping Temporal proximity: sounds in rapid progression tend to befrom the same source Onset and offset: sounds that stop and start at different timestend to be from different sources Good continuation (Demo, Leyenda): sounds that stay constantor change smoothly are often produced by the same source Experience (Mystery song): you can perceptually group soundstogether if know how they should be groupedProf. Greg Francis3PSY 310: Sensory and Perceptual ProcessesPurdue UniversityVision and audition Often times vision and audition work together to produce aunified perceptual experience Vision can help guide auditory grouping Sound can help guide visual grouping Sometimes they conflict McGurk effect demoPurdue UniversityConclusions Lots of issues in sound quality Complicated engineering Involve both physical space Temporal groupingPurdue UniversityNext time Review for Exam 3 Take exam 3 Finish up the course with Touch Smell
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