Loudness and pitch

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Loudness and pitch

  1. 1. Ozarks Technical Community College HIS 110: Acoustics & Psychoacoustics
  2. 2. Intensity and Loudness  Recall that intensity is an acoustic property of sound that can be physically measured  Unit of measure is the decibel (dB)  Loudness is a psychoacoustic property of sound, in that it represents our human perception of how “loud” or “soft” sounds of various intensities are.  Units of measurement include the phon and sone
  3. 3. Things to remember…  Ours ears do NOT have a flat frequency response  They are more sensitive in the mid-frequencies (500- 5000 Hz) than at other frequencies  the average normal hearing person has a threshold of 7 dBSPL at 1000 Hz, but it requires almost 50 dBSPL to hear a sound at 125 Hz.
  4. 4. What is a phon?  A basic measure of loudness  The loudness of a 1000 Hz pure tone at 40 dB=40 phons  The 40 phon curve represents the sound intensity that is required at each frequency to sound equally loud to a 1000 Hz tone at 40 dB.  Refer to Figure 7.1 (Lass & Woodford)
  5. 5. Equal Loudness Contours  Originally measured by Fletcher and Munson (1933)  Represent the relationship between the measured sound pressure level and the perceived loudness of the sound  The curves show how loud a sound must be in dB SPL to be perceived as being of the same loudness as a 1 kHz tone of a given level Image from: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/
  6. 6. How was the phon scale developed?  Basically, you have a patient in the soundfield and you present a 1000 Hz tone at 40 dBSPL.  The patient has a turn-dial knob and they are instructed to adjust the volume of the subsequent sounds of different frequencies until it is equally as loud at the 1000 Hz tone at 40 dBSPL.  This created the 40 phon curve.  This process was repeated at the different input levels. (i.e. 1000 Hz tone at 70 dBSPL to create 70 phon curve)
  7. 7. Phon vs. Sone  The phon scale provides us with a basic scale of loudness. It tells us that one sound is louder than another.  The sone scale can tell us how much louder one sound is than another. (i.e. 2x as loud, 4x as loud).
  8. 8. Sone Scale  1 sone=40 phons  A change of 10 dB results in a doubling or halving of the perceived loudness.  A 1000 Hz tone at 40 dB is perceived as being half as loud as a 1000 Hz tone at 50 dB.
  9. 9. Keep in mind…  Practically speaking, you will never use these measures.  They are more important to audio engineers who are developing high-end audio equipment and sound equalizers.
  10. 10. The Noy  The psychoacoustic unit of measure to quantify a subjects perception of the noisiness or annoyance of a sound is termed the NOY.  The noy includes the presence of high frequency components, intermittent presentation, changes in frequency and intensity, and impulse components that all contribute to the perceived “noisiness” of a sound.  Due to its limited research, this is enough said, regarding the noy.  One person’s “music” is another person’s “noise”.
  11. 11. Frequency and Pitch  Recall that frequency is an acoustic property of sound that can be physically measured  Unit of measure is the hertz (Hz)  Pitch is a psychoacoustic property of sound, in that it represents our human perception of how “high” or “low” sounds of various frequencies are.  Unit of measure is the mel
  12. 12. What is a mel?  The mel scale was developed in 1937 by S.S. Stevens  The pitch of a 1000 Hz tone at 40 dB SPL=1000 mels  2000 mels is equivalent to a pitch that sounds twice as loud as a 1000 mel tone  The mel scale is not linear  Doubling the perceived pitch does not equate to doubling the frequency  i.e. 1000 mels=1000 Hz, but 2000 mels is NOT equal to 2000 Hz
  13. 13. The Mel Scale
  14. 14. How was the mel scale developed?  By “fractionalization” of a pure tone pitch  a pure tone pitch at forty phons of loudness was presented and the subject was instructed to turn the dial to find a pitch that was half the pitch of the first, a third the pitch of the first, etc.
  15. 15. Pitch Perception Phenomena  When two tones of different frequencies (i.e. 500 and 700 Hz) are simultaneously presented at high intensity levels, a low frequency difference tone may be heard (i.e. 200 Hz) by the listener.  A summation tone may occur instead of a difference tone. For example, a 1000 Hz tone plus a 500 Hz tone may be perceived as a 1500 Hz tone. This is not as commonly occurring as a difference tone.  The greater the intensity of a frequency the more likely it is perceived at either a lower or higher frequency pitch.  Lower pitched tones are perceived to be of a lower frequency with intensity increase  Higher pitched tones are perceived to be even higher with greater intensity.  This pitch change by intensity has little effect in the frequency areas between 500Hz and 2KHz.
  16. 16. Timbre  Timbre is composed of the whole spectrum of sound— not just the pitch.  It is what differentiates musical instruments.  A trumpet, a piano, and a flute each produce a pitch of C on the musical scale; however, each sounds differently due to its TIMBRE.
  17. 17. Take Home Message  Though you will likely never use the phon, sone, or mel clinically, it is very important to understand that loudness, pitch, and complex noise perceptions vary by frequency and from person-to-person.  All of these measurements were made on NORMAL listeners.  This will become critical when applying amplification to pathologic residual hearing ability.

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