In acoustics, a sound image refers to the perception of the location or position from which a sound appears to originate. It is the subjective auditory sensation that allows us to localize sounds in our environment.
When we hear a sound, our brain processes various cues to determine the direction and distance of the sound source. These cues can be classified into two types: binaural cues and monaural cues.
Binaural Cues: Binaural cues are based on the differences in sound arriving at both ears. They include:
Interaural Time Difference (ITD): The slight time delay between when a sound arrives at one ear compared to the other ear. The brain analyzes this delay to determine the horizontal direction of the sound source.
Interaural Level Difference (ILD): The difference in sound level between the two ears. When a sound source is closer to one ear, it will be louder in that ear. The brain uses this difference to perceive the horizontal location of the sound.
Head-Related Transfer Function (HRTF): The unique filtering effects of our head, ears, and torso on incoming sound. HRTF helps us perceive the elevation and front-back location of a sound source.
Monaural Cues: Monaural cues are based on the characteristics of sound as received by a single ear. They include:
Spectral Cues: The way frequencies are affected by the shape of our outer ear (pinna). These cues help us perceive the elevation and front-back location of a sound.
Head-Related Impulse Response (HRIR): Similar to HRTF, HRIR describes the filtering effects of our head and ears on incoming sound, helping us perceive the direction and distance of a sound source.
By combining these cues, our brain creates a perceptual representation of sound location, which is known as the sound image. It allows us to perceive sounds as coming from specific directions, whether they are in front, behind, above, below, or to the sides of us.
Creating accurate sound images is essential in audio engineering, sound reproduction systems, and virtual reality applications to provide a realistic and immersive auditory experience.