Intensity

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Intensity

• Scales
• Exponents
• Logarithms
• dB
• dB SPL

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Scales

• Linear
• Ratio

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Exponents

• Shorthand method of displaying very large or
  small numbers
• Numbers greater than 1 involve positive exponents
• Numbers less than 1 involve negative exponents

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Logarithms

• Base 10 logarithms used in the decibel
• Examples
• 1000 10 4 4
• 1 10 0 0
• .001 10 -3 -3

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Decibel

• Standard measure of intensity
• dB 20 (log Po / Pr)
• Where Po pressure output
• Where Pr pressure reference

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dB SPL

• Decibel Sound Pressure Level (dB SPL)
• Standard reference level.
• dB SPL 20 (log Po / 20µPa)
• Where Pa Pascal (measure of force)
• dB SPL 20 (log Po / .0002 dynes/cm2)
• Where dynes are a measure of force

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Constructive and Destructive Interference

• Involves addition of two or more waveforms
• Constructive - 0 to 120 degree phase difference
• Destructive - 120 to 180 degree phase difference
• Note go to oscilloscope program

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Standing Waves

• Reflection of waveforms resulting in areas of
  constructive and destructive interference
• Anti-nodes are areas of constructive
  interference.
• Nodes are areas of destructive interference.

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Complex Auditory Stimuli

• Complex periodic waves
• Complex aperiodic waves

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Complex Periodic Waves

• Addition of sine waves
• Note check oscilloscope
• Always repeat themselves over time
• and therefore have a period.
• Always have a fundamental frequency
• Fundamental is the largest common denominator of
  a group of component frequencies
• Always have harmonic frequencies
• Harmonics are are whole number multiples of the
  funamental
• e.g., 1H, 2H, 3H, etc.

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How are complex periodic waves displayed?

• Waveform
• Amplitude Spectrum (line spectrum)

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Complex Aperiodic Waves

• Does not repeat over time
• Does not have a fundamental frequency
• Does not have harmonics

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How are complex aperiodic waves displayed?

• Waveform
• Amplitude spectrum (continuous spectrum)

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How is Sound Analyzed?

• Sonograph or Spectrograph
• Note Display a spectrogram
• Sound level meter
• Oscilloscope and frequency counter
• Fourier and real time analyses

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Sound Level Meter
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Sound Level Meter

• Sound Pressure Level (linear)
• dBA, dBB, dBC (weighted scales)

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Other Methods of Analysis

• Oscilloscope (displays waveform)
• Frequency Counter

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Other Methods of Analysis

• Fourier Analysis
• A method of mathematically changing a waveform to
  an amplitude spectrum
• Real Time Analysis
• Fourier analysis on the fly

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