A Large Gap at the Level of My Head
New York, U.S.A.
A Large Gap at the Level of My Head
“In contrast to the sound event existing in reality, the auditory event takes place only in the “imagination” of the listener, and it cannot be “proven” by applying measurement techniques. It is rather perceived or felt, either consciously or unconsciously. Sometimes an auditory event occurs even without a corresponding mechanical vibration or sound event. ... Since all sound events take place in the real physical space, the latter can also be called sound space. Auditory events, however, occur in a space, which exists solely in the imagination of the listener. This “imaginary” space will correspondingly referred to as auditory space.” (Mackensen, 10-11)
“Imaginary” does not equal to “non-existing.” Auditory cues were taken to ‘localize’ in the “imaginary” space.’ The process does not always link with ‘navigational’ aspect of aural sensing. Experiencing such ‘auditory space’ in acoustic environment is not so rare. Even in the daily routines, you may hear the sine wave-like sound in pitch higher than around 7000 Hz, or simple microphone feedback accidentally (or purposely) triggered on stage. As you tilt and/or twist your head, your left side and right side of ears will receive different tones far apart in pitch.
Among the auditory cues Mackesen lists, ‘Listener cues’ are useful to breakdown the ‘Gap in the Head’: 1) Interaural Cues (binaural) – A binaural presentation requires both ears. Compared with the monaural presentation in this case a second ear signal, and thus possibly interaural cues, is available. These cues maybe interaural level differences (ILD), interaural phase differences (IPD), interaural time differences (ITD), or combination of those.
Especially interesting is ILD that is difference in sound pressure level reaching the two ears. Reduction in sound level occurs for high frequency sounds for the far ear. The reason why such ‘acoustic shadow’, occurs only for high frequency is as follows. You can imagine frequency as if ripples on the surface of water (difference between sound waves and water ripples is that the sound waves go in the middle of the air while water ripples occur on the surface of water.) More numbers of waves per second become higher frequencies (and shorter wavelength.) When the wavelength of the sound becomes greater than the diameter of one’s head, the ‘shadowing’ would not occur as much.
Studies on the ‘auditory space’ saw development in the last two decades aiming to create virtual 3D aural environments for headphone use, especially true in gaming industries. Atwood stated, “Your pinnae – the outer parts of your ears – strongly influence sound waves that pass through and bounce off them. 3D game audio uses Head Related Transfer Function (HRTF), algorithms to fake the effects of the pinnae, the head and various listening environments, so that injecting the sound straight into the ear canal can produce the impression of real 3D audio sources. When you’ve got HRTF-messaged two-channel audio already, for instance when you’re playing a game, headphones are obviously the best way to get the sound into your head. There’s no way for speakers to do the job as well, because there’s no way for them to stop each ear hearing the sound that’s intended for the other.” (Atwood, “Coding Horror” par 4-5, 2006.)
As none of us has identical shape of pinna to others, creating accurately simulated 3D sound environment ‘acoustically,’ is extremely hard. Laboratories use dummy heads with varieties of dummy pinnas trying to collect diverse HRTF data to achieve most common environment. The complex nature of acoustic aural sensing with combinations of acoustic shadows, ITD, ILD, HRTF, and dynamic cues, necessary for human aurally sensing the space, is contributing to enrich aural experiences in daily life – unfakable for virtual aural space with headphones (as of yet.)
A Large Gap… cannot be recordable, as the large part (or at least the half) of the work takes place in your head. The piece is the combination of ‘sound event’ and ‘auditory event.’ While there is the sound event takes place within the room, each individual’s experience is unique (from another person in the same room – even the ones entering together,) depending on their positions of where they are standing/sitting, their head, and shapes of their pinna, torso, types of outfit, etc. The original sound event won’t yield or aim at a single common experience, but rather impose a unique auditory event to each listener. It is also a study of listening, not about the source of the sound, but about phenomena of perceived.
o.blaat (Keiko Uenishi), May 2009