Perception of Sound

Accordingly, the act of hearing has both subconscious and conscious effects. Subconscious effects, such as hearing loss, are due to prolonged exposure to high sound pressure levels. Conscious effects are a direct result of the ears' acute response to a sound and how the cognitive part of the brain evaluates the sound. An example of an acute response to a sound is the pain and resultant ringing felt in the ear when a whistle is blown close to the ear in an enclosed environment. An example of utilizing conscious response is using sound to convey information to consumers, such as designing a product to emit sounds that indicate operation and/or status. Psychoacoustics is the field of study that seeks to better understand our perception of sound by investigating its conscious effects.

For speech and music, the verbal content conveys much of the information. Furthermore, for speech, music, and many other sounds, the physical characteristics of the sound produce hearing sensations in the listener. The table below lists three primary physical characteristics of sound and their corresponding hearing sensations.

These three hearing sensations directly correlate with their corresponding physical characteristic. However, human hearing is a complex system and many sensations do not correlate directly to just one physical characteristic. For example, in the table above, the sensation of pitch is also dependent on the sound pressure level.

Much of the challenge in the field of psychoacoustics stems from the fact that different listeners perceive identical sounds differently. Age, gender, nationality, and many other diversity factors affect human perception. In addition to this challenge of a heterogeneous population, consumer expectations vary based on the different types of products they purchase. For example, a customer expects different sound characteristics from motorcycles, dishwashers, and personal computers. Therefore, sound quality evaluations are usually specific to the type of product and the target consumer.

There are three basic components to a sound quality program: calibrated recording, listening evaluations, and preference models. The audio recording and the playback must not have any distortion and must be calibrated to the sound pressure level. The goal of sound quality measurement is to develop the preference model, or the basis for future evaluation of sounds.

Because hearing is one of the integral processes through which humans receive information and because the sound of a product carries so much information, there is significant, ongoing research to classify hearing sensations and correlate these sensations to physical characteristics of the signal. Through ongoing investigation, researchers continue to identify physical characteristics of interest and propose improved objective sound quality metrics that correlate better to human perception.