Electrical audio signal processing systems and devices – Binaural and stereophonic – Pseudo stereophonic
Reexamination Certificate
1999-11-29
2003-04-22
Harvey, Minsun Oh (Department: 2644)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Pseudo stereophonic
C381S310000
Reexamination Certificate
active
06553121
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to acoustic processing technology, and more particularly to a three-dimensional acoustic processor which provides a three-dimensional acoustic effect to a listener in a reproducing sound field via a headphone or the like.
2. Description of Related Art
In general, to achieve accurate reproduction or location of a sound image, it is necessary to obtain the acoustic characteristics of the original sound field up to the listener and the acoustic characteristics of the reproducing sound field from the acoustic output device, such as a speaker or a headphone, to the listener. In an actual reproducing sound field, the former acoustic characteristics are added to the sound source and the latter characteristics are removed from the sound source, so that even using a speaker or a headphone it is possible to reproduce to the listener the sound image of the original sound image of the original sound field, or so that it is possible to accurately localize the position of the original sound image.
In the past, in order to add the acoustic characteristics from the sound source to the listener of the original sound field and remove the acoustic characteristics of the reproducing sound field from the acoustic output device such as a speaker or a headphone up to the listener, a FIR (finite impulse response, non-recursive) filter having coefficients that are the impulse responses of each of the acoustic spatial paths was used as a filter to emulate the transfer characteristics of the acoustic spatial path and the reverse of the acoustic characteristics of the reproducing sound field up to the listener.
However, when measuring the impulse response in a normal room for the purpose of obtaining the coefficients of an FIR filter in the past, the number of taps of the FIR which represent those characteristics when using an audio-signal sampling frequency of 44.1 kHz is several thousand or even greater. Even in the case of the inverse of the transfer characteristics of a headphone, the number of taps required is several hundred or even greater.
Therefore, when using FIR filters, there is a huge number of taps and computation required, causing the problems that in an actual circuit implementation it is necessary to have a plurality of parallel DSPs or convolution processors, this hindering a reduction in cost and the achievement of a physically compact circuit.
In addition, in the case of localizing the sound image, it is necessary to perform parallel processing of a plurality of channel filters for each of the sound image positions, making it even more difficult to solve the above-noted problems.
Additionally, in an image-processing apparatus which processes images which have accompanying sound images, such as in real-time computer graphics, the amount of image processing is extremely great, so that if the capacity of the image-processing apparatus is small or many images must be processed simultaneously, the insufficient processing capacity produces cases in which it is not possible to display a continuous image, and the image appears as a jump-frame image. In such cases, there is the problem that the movement of the sound image, which is synchronized to the movement of the visual image, becomes discontinuous. In addition, in cases in which the environment is different from the expected visual/auditory environment of, for example, the user's position, there is the problem of the apparent movement of the visual image being different from the movement of the sound image.
SUMMARY OF THE INVENTION
In consideration of the above-noted drawbacks of the prior art, an object of the present invention is to perform linear predictive analysis of the impulse response which represents the acoustic characteristics to be added to the original signal for the purpose of adding characteristics to the acoustic characteristics, the linear predictive coefficients being used to form a synthesis filter, thereby greatly reducing the number of filter taps, so as to achieve such effects as reduction in size and cost of the related hardware, and an increase in the processing speed achieved thereby. In the case of performing the above-noted linear predictive analysis and using a filter of lower order than the original number of impulse response samples to approximate the frequency characteristics, a three-dimensional acoustic processor is provided in which in particular in the case of high complexity in which the sharp peaks and valleys existing in the original impulse response frequency characteristics, in order to prevent a loss of approximation accuracy, before the linear predictive analysis is performed, to eliminate any auditory change the frequency characteristics of the original impulse responses are smoothed and compensated in the frequency domain, thereby approaching the original impulse response frequency characteristics and enabling a reduction of the number of filters without causing a change in the overall acoustic characteristics.
Another object of the present invention is to provide a three-dimensional acoustic processor in which the acoustic characteristics from a plurality of positions from which a sound image is to be localized are divided into characteristics common to each position and individual characteristics for each position, the filters which add these being disposed in series to control the position of the sound image, thereby reducing the amount of processing performed. In the case in which the sound image is caused to move, by localizing a single sound image at a plurality of locations and controlling the difference in acoustic output level between the different locations, the sound image is smoothed therebetween, interpolation being performed between the positions of the visual image which moves discontinuously, thereby achieving moving of the sound image which matches the thus interpolated positions. In addition, a three-dimensional acoustic processor is provided wherein, in the case in which a reproducing sound image is reproduced using a DSP (digital signal processor) or like, to avoid complexity of registers and like, and to perform the desired sound image localization, localization processing is performed for only the required virtual sound source.
According to the present invention, a three-dimensional acoustic processor is provided which localize a sound image using a virtual sound source, wherein the acoustic characteristics to be added to the sound signal are formed by a linear synthesis filter having filter coefficients that are the linear predictive coefficients obtained by linear predictive analysis of the impulse response which represents those acoustic characteristics, the desired acoustic characteristics being added to the above-noted original signal via the above-noted linear synthesis filter.
The above-noted linear synthesis filter includes a short-term synthesis filter having an IIR filter configuration and which uses the above-noted linear predictive coefficients which adds the desired frequency characteristics to the above-noted original signal, and a pitch synthesis filter having an IIR filter configuration and which uses the above-noted linear predictive coefficient which adds the desired frequency characteristics to the above-noted original signal. The above-noted pitch synthesis filter is formed by a pitch synthesis section with regard to direct sounds with a large attenuation factor, a pitch synthesis section with regard to reflected sounds with a small attenuation factor, and a delay section which applies a delay time thereto. Furthermore, the inverse acoustic characteristics of an acoustic output device such as a headphone or a speaker are formed by means of a linear predictive filter having filter coefficients which are the linear predictive coefficients obtained by linear predictive analysis of the impulse response which represents the acoustic characteristics thereof, the acoustic characteristics of the above-noted acoustic output device being eliminated via this filter. The above-
Matsuo Naoshi
Suzuki Kaori
Fujitsu Limited
Harvey Minsun Oh
Staas & Halsey , LLP
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