The stimuli for hearing, or audition, are ____________, which have several physical characteristics. The physical characteristic of amplitude or height of sound waves is transformed into the subjective experience of ____________, which is measured in units called ______________ . The frequency (cycles per second) of sound waves is transformed into the subjective experience of _________________-, which for humans range from about 20 to 20,000 Hertz (HZ), the unit of measure for frequency.