Chapter 11 Sound the Auditory System and Pitch Perception I The Sound Stimulus a Sound medium i Physical definition the pressure changes in the air or other 1 Answers the tree falling question as yes ii Perceptual definition the experience we have when we hear 1 Answers the tree falling question as no b Sound as a physical stimulus i Sound stimulus occurs when the movements or vibrations of an object cause pressure changes in air water or any other elastic medium that surrounds the object ii Condensation when the diaphragm of the speaker moves out it pushes the surrounding air molecules together causing a slight increase in the density of molecules near the diaphragm and resulting in a local increase in the air pressure that is superimposed on the atmospheric pressure iii Rarefaction when the speaker diaphragm moves back in air molecules spread out to fill in the increased space causing a slight decrease in air pressure iv Alternating high and low pressure regions in the air as neighboring air molecules affect each other 1 Sound Wave pattern of air pressure changes travels through air at 340 meters per second c Pure Tone occurs when pressure changes in the air occur in a pattern described by a mathematical function called a sine wave i Specific tones have this pattern of pressure changes these tones are occasionally found in the environment ii Ex person whistling high pitched tones from a flute iii 2 characteristics of a pure tone amplitude and frequency iv Amplitude size of the pressure change 1 Found by indicating the difference in pressure between the high and low peaks of the sound wave 2 Higher amplitudes associated with louder sounds v Decibel unit of sound which converts the large range of sound pressure into a more manageable scale dB 20 x logarithm p po dB decibels p sound pressure of the stimulus po standard sound pressure 20 micropascals 1 20 micropascals a pressure near the threshold for human hearing 2 Note log 1 0 log 10 1 log 100 2 dB 20log p po 20log 20 20 20 x log 1 20 x 0 0 dB SPL 1 SPL Sound Pressure Level indicates that we have used the standard pressure of 20 micropascals a po in our calculation 2 Sound Level term used when referring to the decibels or sound pressure of a sound stimulus 3 Rule of thumb when multiplying p used in the equation by 10 20 dB will be added to the final sum for example dB 20 x log 20 20 20 x log 1 20 x 0 0 dB SPL dB 20 x log 200 20 20 x log 10 20 x 1 20 dB SPL dB 20 x log 2000 20 20 x log 100 20 x 2 40 dB SPL a Thus a large increase in amplitude causes a much smaller increase in DB vi Frequency the number of times per second that the pressure changes repeat 1 The physical measure associated with the perception of pitch higher frequencies associated with higher pitches 2 Hertz Hz units of frequency 1 Hz 1 cycle per second 3 Humans can perceive frequencies from 20 20 000 Hz vii Pure tones are rare in the environment because various sounds we typically hear tend to have waveforms that are more complex than the pure tone s sine wave pattern of pressure changes d Complex Tone i Fundamental Frequency the repetition rate of a complex tone ii Consist of a number of pure tones 1 Additive Synthesis a number of sine wave components are added together to create the complex ones a The starting point for creating a complex tone by additive synthesis is a single pure tone with the frequency equal to the complex tone s fundamental frequency when more pure tones are added each will have a frequency that is a multiple of the fundamental b Harmonics additional tones added are higher harmonics of the tone c First Harmonic the fundamental frequency which is at the starting point of the additive synthesis that occurs when a complex tone is being built d Addition of harmonics through additive synthesis is how a complex tone is born e Removing the first harmonic the fundamental changes the tone s waveform but the rate of repetition will remain the same e Perceiving Sound 2 Frequency Spectra another way to represent the harmonic components of a complex tone aside from drawing out waveforms the position of each line on the horizontal axis indicates the harmonic s frequency and the height of the line indicates the harmonic s amplitude i Amplitude physical loudness perceptual ii Frequency physical pitch perceptual iii Loudness the quality most closely related to the amplitude or sound pressure which is also called the level of an auditory stimulus 1 Decibels associated with loudness 2 Experiment found that increasing the sound level by 10 dB 3 nearly doubles the sound s loudness Important to keep in mind while decibels are a physical measure loudness is a psychological measure iv Pitch the attribute of auditory sensation in terms of which sounds maybe ordered on a musical scale 1 Low fundamental frequencies are associated with low pitches tuba high fundamental frequencies are associated with high pitches piccolo 2 Tone Height the perceptual experience of increasing pitch that accompanies increases in a tone s fundamental frequency a Tone height increases as we move from the low to the high end of the piano keyboard 3 Tone Chroma the letters of the notes A B C D E F and G repeat and we notice that notes with the same letter sound similar because of this similarity we say that notes with the same letter have tone chroma a Every time we pass the same letter on the keyboard we have gone up an interval called an octave b Tones may be separated by octaves but they still will have the same tone chroma each of the A s has the same tone chroma c Notes with the same chroma have fundamental frequencies that are multiples of one another A1 27 5 A2 55 A3 110 d This explains why a male with a low pitched voice and a female with a high pitched voice can be regarded as singing in unison even when their voices are separated by an octave 4 Effect of the Missing Fundamental the constancy of pitch even when the fundamental or other harmonics are removed a Periodicity Pitch the pitch that we perceive in tones and that has had harmonics removed b So although removing the fundamental does not affect a tones pitch it does cause a tone to sound different v Range of Hearing we hear sound only within a specific range of frequencies 1 Audibility Curve human range of hearing is depicted in this curve which indicates the threshold for hearing determined by free field presentation listening to a loud speaker versus frequency a Range of hearing is between 20 20 000 Hz b We are most