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
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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 [phone] fax [phone]
• 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
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