Sound maskingPsychophysical experiment which examines how one sound affects the perception of another. Two basic types: tonal masking and noise maskingTonal maskingHow much does one pure tone impair perception of another?
Constant Target Hz, Varying Masker Hz
Test tone of fixed frequency and amplitude is chosen then masking tones of different frequencies presented and observer adjusts its intensity until it just drowns out the test tone.
Most effective mask is at the same frequencyNoise maskingHow much does aperiodic sound impair perception of tones?
Varying Target Hz, Constant Masker Hz
Narrow-band white noise means aperiodic sound with frequencies in a certain limited range and effect on absolute threshold for pure tones across the frequency spectrum is measured
Threshold most elevated for the test tone near the frequency of the noise
and is more effective against higher Hz
Subtracting the baseline from the masked audibility threshold gives the threshold elevation.Why do masking asymmetries occur?How the basilar membrane responds to pure tones - the travelling wave build up gradually and then suddenly collapses
Masking tones will be more similar if the mask is lower in frequency than the testFrequency & PitchAs frequency increases, tone height increases linearly while tone chrome changes in a circular fashionAuditory localizationAuditory space - surrounds an observer and exists wherever there is sound
Azimuth - left to right
Elevation - up and down
Distance - position awaySound location accuracyPeople can localize sounds directly in front of them more accurately than those to the side and behindBinaural cuesLocations cues based on the comparison of signals received by the left and right ears
Interaural Time Difference
Interaural Intensity DifferenceInteraural time difference (ITD)Difference between the times sounds reach the two earsInteraural Intensity Difference (IID)Difference in sound pressure level reaching the two ears
Higher the frequency of the sound, the greater intensity difference between the two earsAcoustic shadowCast by the head, does not occur for low frequency sounds which diffract around the headCones of confusionCan't tell where a sound is coming fromMonaural cueHead-Related Transfer FunctionHead-Related Transfer FunctionThe patterns of increases and decreases of sounds are modified by the head's structure (reduced in amplitude, construction interference)
Differs depending on the elevation of the sound sourceHofmann experimentLocalizing sounds after pinna mould was inserted - when from low to high in 19 days. After removal, stayed high.SpectrumHigh frequencies quickly dampened by airMovementMotion parallax: nearly sources pass faster than distant sound sourcesReflectionIn enclosed areas, direct sound arrives at the listener's ears without being reflected off a wall. Reflected sound arrives later, after bouncing off a wall.Free-field presentationSounds presented by speakers located around the listener's head in a dark sound-proof room although equipment is expensiveHeadphone presentationApplied IIDs, ITDs and HRTFs but cues from pinna are eliminated so sound is internalized. Can be externalized by measuring HTRF and applying it to the presented soundsInter-aural time difference detectorsNeurones that respond to specific ITDs in the auditory cortex and at the first nucleus in the system that receives input from both earsTopographic mapsMaps in subcortical structures that have receptive fields for sound location. Panoramic neurones have been found in that signal location by their pattern of firingAuditory sceneArray of all sound sources in a listener's environmentAuditory Scene AnalysisProcess by which sound sources in the auditory scene are separated into individual perceptions. Not in the cochlea; combined together in the pattern of vibration of the basilar membraneAspects of auditory scene analysisSegregation of sound signal into those coming from individual sources
Grouping of separate sounds into those coming from a given source
Sound localizationGestalt HeuristicsWhich elements of a scene belong to which objects
Which elements represent edges between an object and its backgroundPrinciples of auditory groupingProximity
Similarity
Smoothness
Tend to be similar if coming from the same sourceAuditory streamingWhen A and B are similar in pitch, they are grouped together in a single galloping sound stream based on proximity in time and timbre
When A and B are different, they are grouped into two streams, one for low-pitched A sounds and another for high-pitched B soundsMelodic channelingStimuli were two sequences alternative between left and right ears. Smooth sequences perceived by grouping the sounds by similarity in pitchWessel's Timbre IllusionSmoothness heuristic tries to group by smoothly changing pitch which dominates at low speeds. Similarity heuristic tries to group by timbre, dominates at high speedsGood Continuation HeuristicIn silence condition, listeners perceived that the sound stopped during the gaps and in the noise condition, the perception was that the sound continued behind the noise.Effects of experienceWhen to known melodies were interleaved, listeners reported hearing a meaningless jumble unless they were told to listen for somethingVision and soundBalls moving without sound appeared to move past each other while balls with an added click appeared to collide
