2 ch sound field reproduction systems
OSS 2 ch sound field reproduction system
The Ortho-Stereophonic System (OSS) is a system designed to reproduce the actual recording sound field in an anechoic room or listening room using two speakers.
This system is capable of reproducing audible omnidirectional sounds that are generally difficult to achieve with normal stereo playback, including "up/down" and "front/back," as if the listener were actually situated in the space virtually.
Humans are said to hear sounds from various directions based on differences in sound pressure levels reaching ears, phase differences, and other factors. Therefore, in principle, any sound field should be reproducible by controlling the sound pressures perceived at both ears of the listener.
Based on this principle, the OSS control the sound pressure at the listener's external auditory canal in the reproducing sound field to match the sound pressure recorded at the external auditory canal in the sound field to be recorded and reproduced.
To utilize the OSS, at first, a dummy head microphone must be used to record the sound field to be reproduced.
Next, the dummy head microphone is then set in the sound-reproducing sound field and the impulse responses including head-related transfer function (HRTF) are measured.
Before presenting the recorded sound, the recorded sound is then processed using the digital filters that eliminates crosstalk components in the sound-reproducing sound field. At this point, noise cancellation technology is used to process the sound reproduced by the speakers to match the recorded sound-pressure waveform at both ears of the listener. This allows a realistic reproduction of the sound field using two speakers rather than numerous speakers as required with 5.1 ch surround systems.
Although reproduction systems using headphones are more common for stereophonic sound reproduction, it is difficult to localize the sound at a position away from the sound source and to reproduce low-frequency sounds. Moreover, the sound field being reproduced may vary with headphones depending on how the headphones are worn. At Nihon Onkyo Engineering, our sound-reproducing system uses speakers, allowing for superior playback compared with headphone-based playback systems for the reasons mentioned above.
Case study — Designing and evaluating sound fields such as concert halls
In general, acoustic spaces such as concert halls are designed with a focus on reverberation time and the energy of early-reflected sounds. Various room acoustic indexes have been proposed and widely used for associating the performance of a sound space with subjective evaluation values.
However, using only the measured acoustic index values, it is still difficult to understand the spatial sound image without actually hearing the sound.
The OSS is used to provide an "image" of the newly designed room by converting the sound field of the completed room into a database. Combining this system with acoustic simulation technology also allows makes it possible to predict and listen to the sound field from a drawing before actual construction. Utilizing the OSS allows corrections to be made at the design stage and thus allows costs to be reduced substantially.
Case Study — Evaluation of the sound field of vehicle cabin (noises, sound system)
Traditionally, evaluations of sounds in the passenger compartment of a vehicle were done using simple parameter's such as noise level. Nevertheless, even at similar weighted sound-pressure levels, subjective evaluations can differ depending on factors such as timbre. More recent trends have seen positive incorporation of specific sounds instead of simply silence as an added value to sound design. It has become almost impossible to evaluate a sound space using simple acoustic indexes alone. In such situations, a practical and most effective way is subjective evaluation. When performing evaluations using actual vehicles, problems such as driving situation reproducibility and time constraints exist. These problems can be resolved, however, by using the OSS to reproduce the in-vehicle sound field in the lab.
Case study — Three-dimensional acoustic effects at amusement facilities and event venues
In amusement facilities, realistic stereophonic sounds can have enormous effects on listeners. Common stereophonic sound systems include numerous speakers installed in a system that reproduces the intensity and time difference of sounds. However, these systems can be expensive and costly. In principle, the OSS is able to reproduce any sound field with high realism using only two speakers. This allows three-dimensional sound effects to be produced using a relatively small sound-reproduction system.
|Recording system||including dummy head microphone recording system|
|Sound reproduction system||including convolution software, amplifiers and speaker|
|OSS digital filter design system||Impulse response measurement system and OSS digital filter design software|
|Common system||PC with high-performance audio interfaces|