Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod Wilson-Shah
1 ESE250: Digital Audio Basics Week 6 February 19, 2013 Human
Psychoacoustics
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2 Course Map Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric
Kod Wilson-Shah
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Where are we? Week 2 Received signal is sampled & quantized
q = PCM[ r ] Week 4 Sampled signal first transformed into frequency
domain Q = DFT[ q ] Week 3 Quantized Signal is Coded c =code[ q ]
Week 5 signal oversampled & low pass filtered Q = LPF[ DFT(q+n)
] Week 6 Transformed signal analyzed Using human psychoacoustic
models Week 7 Acoustically Interesting signal is perceptually coded
C = MP3[ Q] Over Sample DFT LPF DecodeProduce r(t)r(t) p(t)p(t) q +
n C Perceptual Coding Store / Transmit Q + N Q Week 4 Week 6 Week
5Week 3 [Painter & Spanias. Proc.IEEE, 88(4):451512, 2000] 3
Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah
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4 The Physical Ear External Sound Waves Guided by outer ear
into auditory canal Excite Inner Ear Through mechanical linkage
connecting ear drum to cochlea [R. Munkong and B.-H. Juang. IEEE
Sig. Proc. Mag., 25(3):98117, 2008] Week 6 Psychoacoustics ESE 250
S13 DeHon Kadric Kod Wilson-Shah
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5 The Physical Ear Initiates signal processing frequency domain
analysis Via analog computation Video: CochleaCochlea What part of
the Cochlea vibrates for an 800 Hz square wave? [R. Munkong and
B.-H. Juang. IEEE Sig. Proc. Mag., 25(3):98117, 2008] Week 6
Psychoacoustics ESE 250 S13 DeHon Kadric Kod Wilson-Shah
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6 The Cognitive Ear Modern Psychoacoustics Benefits greatly
from o decades of neural recording o contemporary brain imaging
technology [R. Munkong and B.-H. Juang. IEEE Sig. Proc. Mag.,
25(3):98117, 2008] Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric
Kod Wilson-Shah
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7 Power Spectrum Model of Hearing Rough Picture (main content
of todays lecture): Critical Bands: Auditory system contains finite
array of adaptively tunable, overlapping bandpass filters Frequency
Bins: humans process a signals component (against noisy background)
in the one filter with closest center frequency Masking: certain
signal components in a given band are favored and others are
filtered out Established through decades of psychoacoustic
experiments B.C.J. Moore. Int.Rev.Neurobiol., 70:4986, 2005. Week 6
Psychoacoustics ESE 250 S13 DeHon Kadric Kod Wilson-Shah
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8 Auditory Thresholds In the lab, you varied the frequency,
amplitude and phase of signals What was the effect of each, if any,
on the sound you heard? Frequency Amplitude Phase Week 6
Psychoacoustics ESE 250 S13 DeHon Kadric Kod Wilson-Shah
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Auditory Thresholds Harvey Fletcher (1940) Played pure tones
varying o frequency, f [ Hz] o Intensity, I [Dyn cm -2 ] = 10 -5 [N
cm -2 ] = 0.1 Pa o phase changes tend to be inaudible Large
listener population o Young o Acute Recorded extreme thresholds
faintest audible greatest tolerable Week 6 Psychoacoustics ESE 250
S13 DeHon Kadric Kod Wilson-Shah (http://www.et.byu.edu/)
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10 Auditory Thresholds Results: pain-free hearing range extends
at most over 20 Hz 20 KHz with sensitivity 2 10 -4 0.1 Pa = 20 Pa
Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod Wilson-Shah 0.1
Pa [H. Fletcher. Rev. Mod. Phys., 12(1):4765, 1940].
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11 The decibel unit Define standard pressure: p 0 = 0.0002 0.1
Pa = 20 Pa Threshold of human hearing Compute Sound Pressure Level
as: L SPL = 20 log 10 (p/p 0 ) dB L SPL for p 1 = 20 Pa, for p 2 =
200 Pa, for p 3 = 20 mPa Week 6 Psychoacoustics ESE 250 S13 DeHon
Kadric Kod Wilson-Shah Compare to Ambient sea-level pressure: 1
Atmosphere = 10 5 Pascal Q: why use log-log scale? A 1 : dynamic
range A 2 : loudness is a power function 0.1 Pa
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12 The decibel unit Hearing intensity Week 6 Psychoacoustics
(http://www.dspguide.com/ch22/1.htm)
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13 Lets try to reproduce these results! Week 6 Psychoacoustics
(http://www.dspguide.com/ch22/1.htm) We will listen to single sine
tones starting at a frequency of 10KHz, all the way up to 20KHz, so
each student can figure out their cut-off frequency Suggestions to
improve this experiment?
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14 Animal hearing ranges Dogs: Greater hearing range: 40Hz to
60KHz Ultrasonic dog whistles Mice: Large ears in comparison to
their bodies Hearing range: 1KHz to 70KHz Cant hear low frequency
noises Communicate with high frequency Distress call (40KHz), alert
of predator [Pictures from Wikipedia] Week 6 Psychoacoustics ESE
250 S13 DeHon Kadric Kod Wilson-Shah
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15 Why Sinusoids? Why not some other harmonic series? Fouriers
analysis shows harmonic analysis could be based on arbitrary smooth
periodic fundamental Why does the animal receiver use sinusoids?
Hamiltonian Mechanics Simplest physical model of vibrating masses
Coupled spring-mass-damper mechanics Produce sinusoidal harmonics
Video: CochleaCochlea m x b k . all sound is produced by vibrating
masses . Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah
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16 Masking - Spatial Masking Paradigms Masker masking maskee
Tone Masking Noise o pure tone of 80 SPL at 1 kHz o just masks
critical band noise of 56 SPL centered at 1 kHz Masker-to-Maskee
ratio o Constant for fixed relative frequency and varying amplitude
o Changes with varying relative frequency [T. Painter and A.
Spanias. Proc. IEEE, 88(4):451512, 2000.] 1 Bark frequency interval
Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah
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17 Masking [H. Fletcher. Rev. Mod. Phys., 12(1):4765, 1940].
The first graph shows the masking pattern for a 200Hz tone Mostly
masks tones around 200Hz, but also at harmonics The second graph
shows the same plot for different frequencies, but only the
fundamental part Notice that the band gets wider for increasing
frequencies masker at fundamental can somewhat mask maskees at the
harmonics but the spreading curve is traditionally depicted over
the fundamental only Week 6 Psychoacoustics ESE 250 S13 DeHon
Kadric Kod Wilson-Shah
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18 Tone Masking Noise Week 6 Psychoacoustics ESE 250 S13 DeHon
Kadric Kod Wilson-Shah Are the following signals masked? 200 Hz
tone at 80dB 200 Hz tone at 40dB 300 Hz tone at 40dB 400 Hz tone at
40dB 700 Hz tone at 30dB
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19 Masking [H. Fletcher. Rev. Mod. Phys., 12(1):4765, 1940].
Tone Masking Noise (Fig 12) value above quiet threshold such that a
signal at the abscissa frequency can be heard in presence of top:
200 Hz tone bottom: various frequencies Noise Masking Tone (Fig 13)
dots show pure tone magnitude (in dB) required to be audible above
noise o Of the magnitude on the middle curve o centered at that
frequency o with bandwidth at least wider than the bars of Fig 12
Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah
Slide 21
20 Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah Are the following signals masked by the noise? 200Hz at
60dB 1KHz at 60dB Noise Masking Tone
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21 Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah Are the following signals masked by the noise? 200Hz at
60dB o Yes! 1KHz at 60dB Noise Masking Tone noise
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22 Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah Are the following signals masked by the noise? 200Hz at
60dB o No! 1KHz at 60dB Noise Masking Tone
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23 Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah Are the following signals masked by the noise? 200Hz at
60dB 1KHz at 60dB o No! Noise Masking Tone
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24 Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah Are the following signals masked by the noise? 200Hz at
60dB 1KHz at 60dB o No! Noise Masking Tone
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25 Masking - Temporal Temporal Masking Masker effect persists
for tenths of a second Masker effect is acausal o on ~ 2/100
timescales Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah
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26 Pitch JND JND = just noticeable difference change in
stimulus that just elicits perceptual notice where just means that
a smaller variations of stimulus cannot be discerned [H. Fletcher.
Rev. Mod. Phys., 12(1):4765, 1940]. Week 6 Psychoacoustics ESE 250
S13 DeHon Kadric Kod Wilson-Shah What can you say about the JND:
Below 1000 Hz? o roughly constant o ~ 3 Hz Above 1000 Hz? o roughly
log-log linear o Log[Jnd(f 2 )] - Log[ Jnd(f 1 )] ~ n (Log[f 2 ] -
Log[f 1 ]) Suggests that as frequency increases broader frequency
bands assigned to same length of cochlear tissue Remember cochlea
model What is n? e.g. f 1 =2000 f 2 =4000 6 = 10 4 ~ n( Log 10 [2]
) ) n ~ 20
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27 JND experiment Week 6 Psychoacoustics ESE 250 S13 DeHon
Kadric Kod Wilson-Shah The following audio files contain a single
tone playing for 10 seconds. The sine starts at 200Hz, then changes
to a higher frequency (201, 202, 203, 205, 210). This change occurs
after a number of noises: 1, 2, 3, 4, 5, 6, 7, 8 or 9. Can you
notice when the change happens?
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28 Critical Bands Decades of empirical study reveal that human
audio frequency perception is quantized into < 30 critical bands
of perceptually near-identical pitch classes corresponding to
~equal length bands of cochlear tissue (neurons) Week 6
Psychoacoustics ESE 250 S13 DeHon Kadric Kod Wilson-Shah
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29 Critical Bands: Evidence Tone masking Noise (Fig. a & c)
o noise audibility threshold o for small bandwidth noise o remains
constant o until tone frequency locus o falls away from critical
bandwidth Noise masking Tone (Fig. b & d) o same effect o with
masker and maskee roles reversed [T. Painter and A. Spanias. Proc.
IEEE, 88(4):451512, 2000.] Week 6 Psychoacoustics ESE 250 S13 DeHon
Kadric Kod Wilson-Shah
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30 The Bark Scale Bark units: Uniform JND scale for frequency
Maps frequency intervals into their respective critical band number
[E. Zwicker. J. Acoust. Soc.Am., 33(2):248, February 1961] Week 6
Psychoacoustics ESE 250 S13 DeHon Kadric Kod Wilson-Shah
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31 The Bark Scale Frequency-to-Bark function First Principles
vs. Empirical Modeling [E. Zwicker. J. Acoust. Soc.Am., 33(2):248,
February 1961] Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric Kod
Wilson-Shah
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32 Compression opportunities Week 6 Psychoacoustics ESE 250 S13
DeHon Kadric Kod Wilson-Shah Consider the following recording Any
ways to improve the compression?
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33 Compression opportunities Week 6 Psychoacoustics ESE 250 S13
DeHon Kadric Kod Wilson-Shah Zooming in on a smaller portion Any
ways to improve the compression? 200Hz205Hz Frequency 195Hz 193 194
196 197 198 199 201 202 203 204 206 207 208 dB 80 0 20 40 60 100
120 Masked
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34 Compression opportunities Week 6 Psychoacoustics ESE 250 S13
DeHon Kadric Kod Wilson-Shah Zooming in on a smaller portion Any
ways to improve the compression? 200Hz205Hz Frequency 195Hz 193 194
196 197 198 199 201 202 203 204 206 207 208 dB 80 0 20 40 60 100
120 JND: Could only represent integer frequency values
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35 Compression opportunities Week 6 Psychoacoustics ESE 250 S13
DeHon Kadric Kod Wilson-Shah Zooming in on a smaller portion Any
ways to improve the compression? 200Hz205Hz Frequency 195Hz 193 194
196 197 198 199 201 202 203 204 206 207 208 dB 80 0 20 40 60 100
120
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36 Next Week Week 6 Psychoacoustics ESE 250 S13 DeHon Kadric
Kod Wilson-Shah How can we use what we know about human perception
to compress music? Frequency hearing range Masking o Temporal o
Spatial o JND o Barks
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37 Big Ideas Sound is a pressure wave that makes the Cochlea
vibrate with frequencies from ~20Hz (at the tip) to ~20KHz (at the
base) This vibration is sinusoidal (physics) This is why sound
harmonics are best represented as sinusoidal signals Masking
Temporal A masker tone can mask another tone that is present either
right before or a little after the masker Spatial A single tone can
mask an entire frequency band (that contains the tone) if its
intensity is high enough There are
