Some taxes are inadvertently hidden, but others are consciously designed that way to disguise the cost of government. Itâs easy to see why: the total U.S. tax burden is equal to 56 percent of annual personal consumption spending.
Thus, the volume is proportional to the amplitude of the sound wave. The frequency of a sound wave is perceived as pitch. Humans can detect pitches within the acoustic range of 20 to 20,000 Hz, but we can't detect ultrasound or infrasound.
Our perception of sound is directly related to the physical properties of sound waves (see Figure 3.7). One of the ï¬ rst things that we notice about a sound is how loud it is. Loudness is determined by the intensity, or amplitude, of a sound wave and is measured in units called decibels. Zero decibels represents the loudness of the softest sound that humans can hear, or the absolute threshold for hearing. As decibels increase, per-ceived loudness increases. Pitch refers to the relative âhighnessâ or âlownessâ of a sound. Pitch is determined by the frequency of a sound wave. Frequency refers to the rate of vibration, or number of waves per second, and is measured in units called hertz. Hertz simply refers to the num- ber of wave peaks per second.