Sound can be viewed as a wave motion in air or other elastic media. In this case, sound is a stimulus. Sound can also be viewed as an excitation of the hearing mechanism that results in the perception of sound. In this case, sound is a sensation. These two views of sound are familiar to those interested in audio and music. The type of problem at hand dictates our approach to sound. If we are interested in the disturbance in air created by a loudspeaker, it is a problem in physics. If we are interested in how that disturbance sounds to a person near the loudspeaker, psychoacoustical methods must be used. Because this book addresses acoustics in relation to people, both aspects of sound will be treated.
Sound is characterized by a number of basic phenomena. For example, frequency is an objective property of sound; it specifies the number of waveform repetitions per unit of time (usually one second). Frequency can be readily measured on an oscilloscope or a frequency counter. On the other hand, pitch is a subjective property of sound. Perceptually, the ear hears different pitches for soft and loud 100-Hz tones. As intensity increases, the pitch of a low-frequency tone goes down, while the pitch of a highfrequency tone goes up. Fletcher found that playing pure tones of 168 and 318 Hz at a modest level produces a very discordant sound. At a high intensity, however, the ear hears the pure tones in the 150- to 300-Hz octave relationship as a pleasant sound. We cannot equate frequency and pitch, but they are analogous.
A similar duality exists between intensity and loudness. The relationship between the two is not linear. Similarly, the relationship between waveform (or spectrum) and perceived quality (or timbre) is complicated by the function of the hearing mechanism. A complex waveform can be described in terms of a fundamental and a series of harmonics of various amplitudes and phases. But perception of timbre is complicated by the frequency-pitch interaction as well as other factors.
- Fundamentals of Sound
- Sound Levels and the Decibel
- Sound in the Free Field
- The Perception of Sound
- Signals, Speech, Music, and Noise
- Comb-Filter Effects
- Modal Resonances
- Schroeder Diffusers
- Adjustable Acoustics
- Control of Interfering Noise
- Noise Control inVentilating Systems
- Acoustics of Listening Rooms
- Acoustics of Small Recording Studios
- Acoustics of Control Rooms
- Acoustics of Audio/Video Rooms
- Acoustics of Large Halls
- Acoustic Distortion
- Room Acoustics Measurement Software
- Room Optimizer
- Room Auralization