Concept of Critical Band - Miami Universityjaegerh/PHY131/Week08-MO.pdf · 2007-02-26 · Concept...
Transcript of Concept of Critical Band - Miami Universityjaegerh/PHY131/Week08-MO.pdf · 2007-02-26 · Concept...
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Spring 2006 – Week 8 PHY 131 1
Concept of Critical Band
• Think of the basilar membrane as dividedinto 24 sections, the so-called critical bands
• As long as the frequencies of the complextone are within one critical band, the samegroup of hair cells is involved in “tickling”the nerve ends.
Spring 2006 – Week 8 PHY 131 2
Critical Bandwidth and Loudness
Frequency (Hz)
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Spring 2006 – Week 8 PHY 131 3
Critical Band and Loudness
Spring 2006 – Week 8 PHY 131 4
Critical Band and Frequencyf < 1000 Hz
c.b. ≈ 90-150 Hz
f > 1000 Hz
c.b. ∝ f
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Spring 2006 – Week 8 PHY 131 5
Loudness Summation and c.b.
• If the frequencies are within one c.b.Itot=I1+I2+…determine SILdetermine loudness level and loudness fromequal loudness curves
Spring 2006 – Week 8 PHY 131 6
Loudness Summation and c.b.
• If the frequencies are separated bymore than one c.b.The total loudness approaches (but remainsless) the sum of the individual loudnesses:
S ≤ S1 + S2 + S2…
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Spring 2006 – Week 8 PHY 131 7
Loudness Summation and c.b.
• If frequency separation gets large a simpleloudness determination fails because mostlisteners focus on one tone and judgeloudness based on this tone.
• If the complex tone has many frequencycomponents, loudness determination mustbe done one c.b. at a time (filter banks).
Spring 2006 – Week 8 PHY 131 8
Masking• One tone “covers up” another• More effective when two frequencies are close. If the tones
differ by less than a c.b., the low-f tone will mask thehigher-f tone.
• A pure tone masks a tone of higher frequency more effectivethan a lower frequency
• More intense tones mask a greater frequency range• Masking also occurs by narrow bandwidth noise as long as
the bandwidth is equal or greater than the c.b.
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Spring 2006 – Week 8 PHY 131 9
Frequency Response Curves
Spring 2006 – Week 8 PHY 131 10
Frequency Response Curves(Pairs of Pure Tones)
1046 Hz 523 Hz697 Hz 523 Hz588 Hz 523 Hz
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Spring 2006 – Week 8 PHY 131 11
Response Curves and Masking
Spring 2006 – Week 8 PHY 131 12
Week 8
• Tone Quality (Timbre) and Spectrum
• Spectrum Analysis
• Spectrum Synthesis
• Pitch and its Perception
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Spring 2006 – Week 8 PHY 131 13
Timbre or Tone Quality
• Attack / Decay Transients– Tone envelope
• Spectrum of driving force– Reed, Lips, Bowing, Hammer, Plucking
• Harmonic response of each instrument– Depends on type and shape of instrument– Sounding box/board of String instruments– Formants (especially human voice)
• Inharmonicities:– Finite string size stretches Piano octaves.– Wind harmonics not necessarily pure integers
Spring 2006 – Week 8 PHY 131 14
62 cm-Long Pipe Open at Both Endswaveform
spectrum
-1.00
-0.50
0.00
0.50
1.00
0 5 10 15
Sign
al
[V]
t [ms]
0.0
0.3
0.530.040.050.060.070.080.090.0
100.0
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Pow
er
Spec
trum
[a
rb.
unit
s]
f [Hz]
250 500 750 1000 1250 1500 Hz
T = 4 msf = 1/T = 250 Hz
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Spring 2006 – Week 8 PHY 131 15
31 cm-Long Pipe Open at One Endwaveform
spectrum
-1.00
-0.50
0.00
0.50
1.00
0 5 10 15
Sign
al
[V]
t [ms]
0.0
0.3
0.530.040.050.060.070.080.090.0
100.0
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Pow
er
Spec
trum
[a
rb.
unit
s]
f [Hz]
250 500 750 1000 1250 1500 Hz
T = 4 msf = 1/T = 250 Hz