An OSS (Ortho-Stereophonic System) is a reproduction system that reconstructs recorded sound field in rooms such as an anechoic or listening room using two speakers.
The OSS system can reproduce sound from all directions including 'vertical and horizontal' directions which is usually difficult in stereophonic reproduction. Furthermore, you can feel like you are actually there (virtual reality).
(Actually, the degree of accuracy reproduction varies among individuals).
People recognize sound reaching from all direction by the difference of interaural sound pressure level and phase. Therefore, in principle, it is possible to reconstruct the sound field by controlling the sound pressure level in a listener's ear.
On the basic principle, OSS controls the sound pressure level of listener's ear canal in such a way as to be similar to the level of a dummy head microphone's that recorded in the room.
Using OSS, first, we record sound that we want to reconstruct by using a dummy head microphone.
Then we set up a dummy head microphone in the listening room and measure the impulse response including the head-related transfer function (HRTF). We measure by an impulse response measurement system called 'AEIRM'.
OSS operates the digital signal processing which cancels cross talk components in the listening room.
By using a noise canceling method, OSS processes the sound pressure waveform at the point of listener's ear from speaker in the listening room as to correspond with that in the recording room. In the end, using only 2 speakers can reconstruct the realistic sound field without multiple speaker system, as the 5.1ch surround system.
Also for the 2ch sound field reproduction system a headphone is used as sound playback equipment. It is hard to reproduce an acoustic localization from a distance and at low frequency. When using a headphone, there is concern that the acoustic field might change by the fitting condition. Thus comparing with using headphone system, OSS has high performance of sound reproduction.
Commonly when acoustic field for a concert hall is designed, the reverberation time or the energy of early-reflected sound is focused on. Various interior acoustic parameters are proposed as the value which relates quality of room to subjective evaluated value and measured widely.
However, it is very difficult to describe how people feel the sound in the built room, based only on the acoustic parameters.
When using OSS, we create a database for the acoustic field of a built room and use it as a model for the acoustic sound when constructing a new room. In combination with the acoustic simulation technique, we can predict the acoustic sound at draft level and preview the sound before actually undertaking construction. It enables to modify at the stage of planning. OSS supports to reduce unnecessary cost.
Until now, evaluating the sound in vehicle was done by the simple parameter for noise level. However, even though the noise levels are the same, the subjective response will differ depending on such as the tone. Recently there is a tendency not just to reduce the noise level, but also to design a sound as something extra with introducing a specific sound positively. So, it is difficult to express by simply acoustic parameters. Under these states, an auditory evaluation is a fundamental and effective way. In case of an actual vehicle test, there are problems as the difference of driving condition and the time limit. However, the OSS system enables to re-create the acoustic sound in vehicle, in experimental laboratory, we can solve those problems.
There is a case that the 3-D acoustic has a profound effect in amusement parks. This is a common way to create a 3-D acoustic using several speakers with controlling the intensity and time lag, but this system is expensive and it needs a large room. The OSS system makes it possible to reproduce any actual acoustic sound using 2ch speakers. OSS can create 3-D acoustic effects within a relatively small reproduction system.
| System configuration | |
|---|---|
| OSS Recorder |
dummy head microphone (head and torso simulator), sound recording device (DAT, PC etc) |
| OSS Player | Convolution software, Amplifier, Speaker, Sound playback device (DAT, PC etc) |
| OSS digital filter designer |
Impulse Response Measurement System AEIRM Digital filter design software |
| Common |
Control PC, High quality audio interface |