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Los Angeles Chapter Audio Engineering Society 25 March 2003

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Subjective loudness of a complex tone is fairly complicated. ... analysis of masking...and even in the determination of the pleasantness of music. ... – PowerPoint PPT presentation

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Title: Los Angeles Chapter Audio Engineering Society 25 March 2003


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Los Angeles Chapter Audio Engineering Society25
March 2003
LOUDNESS
  • Neil A. Shaw
  • Menlo Scientific Acoustics, Inc.
  • Topanga, California

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Introduction
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Introduction
5
History
  • p

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History
  • fff
  • ff
  • f
  • mf
  • p
  • mp
  • pp
  • ppp

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History
  • October 22, 1850
  • Gustav Theodor Fechner
  • Ernst Weber, 1829-
  • Two closely related Stimuli
  • Detect - fixed percentage
  • 25 ? JND

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History
  • Sensation cant be measured.
  • JNDs can be measured.
  • ? Sensation could be measured merely by counting
    off the number of JNDs as stimulus increased
    from zero upward.

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History
  • 1860
  • Elements of Psychophysics
  • Fechner invented the field and coined the word.
  • Webers law as stimuli are multiplied,
    sensation increase by addition, i.e., sensation
    grows as the logarithm of the stimulus

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Flectcher Munson - Loudness Level vs Intensity
Level and more
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Thresholds and free-field equal loudness level
contours
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Definitions
  • Intensity level the sound pressure level, or
    sound level
  • LI (dB) 20 log (p/pref)

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Definitions
  • Loudness level (LN) the level, of an equal
    loudness curve labeled by its LI at 1 kHz.. The
    unit of loudness level, LN, is the phon.

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Definitions
  • Loudness The unit of loudness is the sone. A
    loudness N1 is equal by definition to LN 40
    phon, independent of frequency. A loudness of 16
    sone is twice as loud as one of 8 sone and four
    times as loud as one of 4 sone.

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Loudness versus Intensity
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Loudness
  • Subjective loudness of a complex tone is fairly
    complicated. If the frequencies of the tones are
    within the critical band
  • I I1 I2 I3

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Loudness
  • If the bandwidth exceeds the critical bandwidth,
    the resulting loudness is greater than that
    obtained from the simple summation of
    intensities. As the bandwidth increases, the
    loudness increases, but is asymptotic to, the sum
    of the several loudnesses
  • N N1 N2 N3

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Loudness
  • There are various standards used to measure
    loudness.
  • ISO R532 A (Steven)
  • ISO R532 B (Zwicker)

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Loudness
  • ISO R532 A (Stevens)
  • Divide band into octaves (1/1, ½ or 1/3)
  • NT (1-F) N F ? N
  • F is a weighting coefficient

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Loudness
  • ISO R532 B (Zwicker)
  • Divides spectrum into critical bands, convert to
    Bark bands per conversion rules
  • N ? N (z) dz

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0
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Loudness
  • ISO R532 B (Zwicker)


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Loudness
  • ISO R532 B (Zwicker)


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Loudness
  • ISO R532 B (Zwicker)


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Loudness
  • ISO R532 B (Zwicker)


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Loudness
  • Tones within a critical band are sensed according
    to the overall power, so their intensities add
    and the loudness is given by
  • N (critical band) 460 F(f)(? )

1/3
Ii

i
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Loudness
  • Tones differing by more than the relevant
    critical bands are sensed as well-separated
    regions on the basilar membrane and the loudness
    add
  • N ? Ni


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Critical Bandwidths
  • If a subject listens to a sample of noise with a
    tone present, the tone cannot be detected until
    its LI exceeds a value that depends on the amount
    of noise present.

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Critical Bandwidths
  • Fletcher and Munson found that the masking of a
    tone by broadband noise is independent of the
    noise bandwidth until the bandwidth becomes
    smaller than some critical value that depends on
    the frequency of the tone.

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Critical Bandwidths
  • The ear acts like a collection of parallel
    filters, each with its own bandwidth, and the
    detection of a tone requires that its level
    exceed the noise level in a particular band by
    some detection threshold.

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Critical Bandwidths
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Critical Bandwidths
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Critical Bandwidths
  • Nowhere in auditory theory or in acoustic
    psychophysiology practice is anything more
    ubiquitous than the critical band. It turns
    upin the study of loudness, in the analysis of
    maskingand even in the determination of the
    pleasantness of music. J. Tobias, Foundations of
    Modern Auditory Theory.

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Masking in noise
  • Masking is the amount the threshold of audibility
    of a signal is raised in the presence of noise.
  • This masking of signal in critical bands by the
    overall and individual levels in the critical
    bands is the basis for all perceptual coding
    schemes.

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Masking in noise
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Demonstrations
  • Critical bands in masking (tracks 2 to 6)

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Demonstrations
  • Critical bands by loudness comparisons (track 7)

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Demonstrations
  • Loudness scaling (tracks 19 and 20)
  • N (sones) C(f) p0.6

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Demonstrations
  • Asymmetry of masking by pulsed tones (track 22)

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LOUDNESS
  • Menlo Scientific Acoustics, Inc.
  • Los Angeles Office San Francisco Office
  • Post Office Box 1610 5161 Raincloud Drive
  • Topanga, California 90290 Richmond, California
    94803
  • fon 310-455-2221 fon 510-758-9014
  • fax 310-455-0923 fax 510-758-9016
  • China Office Taiwan Office
  • c/o Sea Galleon c/o Kou Ryou Enterprises
  • Jinhaihua Xincun, Chiling, 2/F, 92 Neihu Road,
  • Houjie, Dongguan, Guangdong Section 1, Taipei
  • China Taiwan
  • fon  86-769-5887752, 5817646 fon  886-2-2657
    1100
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