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Classical Measurement Methods
- 1.Method of Limits
- 2.Method of Adjustment
- 3.Method of Constant Stimuli
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Method of Limits
- –Stimulus is presented
- –Subject indicates whether or not they heard it
- –Tester manipulates the level of the stimulus based on the subjects response
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Number of individual presentations of a stimulus
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–Ascending run:
stimulus level begins below threshold and is raised until the subject can barely hear the tone
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Method of Adjustments
- –The subject controls the stimulus level by turning an unmarked knob
- –Stimulus changes in a continuous fashion (rather than in fixed steps)
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Method of Constant Stimuli
- Presents various stimulus levels in random order
- •Like the Method of Limits but not sequential
- –No ascending or descending runs
- -Results are tabulated and plotted as a “psychometric function”
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–Psychometric Function:
- a plot which shows the percentage of times the stimulus was heard at each level
- –Threshold
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subject establishes the relationship between a standard and comparison stimulus
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- Major Approaches to Direct Scaling:
- •Ratio Scales
- •Magnitude Scales
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expresses subjective magnitude of one stimulus as a ratio of the other stimulus
–For example: compared to the standard tone, the comparison tone might be twice as loud
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adjusts the magnitude of a stimulus to produce a specific ratio of the other
–For example: the subject adjusts the intensity of the stimulus until it is twice as loud as the standard tone
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Magnitude Estimation:
- –A series of stimuli are presented that vary in some dimension such as intensity or frequency.
- –The subject assigns a number to each stimulus to represent its loudness or pitch.
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Magnitude Production:
–Physical magnitude adjusted to correspond with numbers indicating perceived magnitude
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Human Hearing Thresholds
- Humans have sensitivity over a broad range of frequencies: 10 Hz – 20,000 Hz
- •Hearing sensitivity is best between 2000 – 5000 Hz
- •Hearing sensitivity is poor below 100 Hz and above 10,000 Hz
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1.Minimum Audible Pressure (MAP):
- based on monaural (one ear) thresholds with earphones
- –Measure sound pressure in the ear canal at threshold
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Minimum Audible Field (MAF):
- based on binaural (two ears) thresholds from loudspeakers
- –Measure sound pressure in sound field at head level
- -MAF thresholds tend to be 6 dB lower (better) than MAP thresholds due to binaural summation
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Upper Limits of Hearing
- •Sounds become uncomfortably loud at a level of about 100 dB SLP
- –This level is fairly constant across frequencies
- •Sounds that evoke feeling or pain occur at levels of 120 – 140 dB SPL
- –Tactile sensations rather than auditory
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Temporal Summation/Integration def
- -trading of duration and intensity
- -When sounds are shorter than approximately 300 ms, threshold (or loudness) depends on duration
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Temporal Summation/Integration
- •As a sound gets shorter
- –Threshold becomes higher (less sensitivity)
- –The sound is perceived as being softer
- •As the sound get longer
- –Threshold becomes lower (better sensitivity)
- –The sound is perceived as being louder
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integration
–a 10-fold decrease in duration is offset by a 10 dB increase in intensity
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Just Noticeable Difference (JND) or Difference Limen (DL):
-the smallest perceptible difference between two sounds
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Absolute Difference Limens:
- –ΔI: smallest intensity change that can be detected
- –ΔF: smallest frequency change that can be detected
- -they specify the absolute physical difference needed to tell two sounds apart
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Relative Difference Limen or Weber Fraction:
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-considers both the absolute DL and the starting point
- -Weber’s Fraction = absolute DL / starting point
- = ΔI/I or Δ F/F
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Intensity Discrimination
- –Weber’s Fraction (ΔI/I) decreases slightly with increasing intensity
- – ΔI/I is about 0.4 near threshold and decreases to 0.2 at higher intensities
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•Frequency Discrimination
- –Weber’s Fractions (ΔF/F) are relatively constant for mid-frequencies (600 – 2000 Hz)
- – ΔF/F is smallest (0.002) between 600 – 2000 Hz, and gets larger for frequencies above and below this range
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our perception of intensity
- •Intensity is a physical attribute of sound
- •Loudness is a perceptual attribute of sound
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Equal Loudness Contours or Phon Curves:
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lines that connect equally loud stimulus levels at different frequencies
- •A way of quantifying loudness
- •How much
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Phons:
- units of loudness defined relative to the loudness of a 1000 Hz tone
- –A 40 dB SPL tone at 1kHz has a loudness of 40 phons, a 50 dB SPL tone at 1kHz has a loudness of 50 phons, etc
•All sounds that are equal in phons have the same loudness level even though physical levels (dB) are different
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Sone:
- another unit of loudness that shows the relationship between loudness and intensity
- •Sone scale compares the loudness of any intensity with the loudness of a specific reference sound
- –Reference = 1 sone = a 1000 Hz tone with an intensity of 40 dB SPL
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Sone Scale
- Loudness (in sones) doubles for every 10 dB increase in intensity
- •Loudness (in sones) is halved for every 10 dB decrease in intensity
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The linear relationship between log loudness and log intensity corresponds to a power relationship between loudness and intensity (in raw units)
- Formula
- Loudness = k * Intensitye
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Critical Bandwidth (CBW):
bandwidth at which a perceptual change occurs
- •Critical Bands are:
- –larger for higher frequencies
- –smaller for lower frequencies
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Pitch:
- our perception of frequency
- •The lowest frequency pure tone that evokes a “tonal” pitch is 20 Hz
- •For a tone to sound “tonal”, it must have a minimum duration of at least 10 – 60 ms in duration depending on frequency
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Mels:
- unit of pitch that parallels the sone unit of intensity
- •Mel scale relates frequency and pitch
- –Reference value
-ratio scale
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Pitch of the Missing Fundamental:
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perceived pitch corresponds to the fundamental frequency, even though the fundamental frequency is not physically present
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