Electrical audio signal processing systems and devices – Binaural and stereophonic – Stereo speaker arrangement
Reexamination Certificate
1997-03-10
2001-01-30
Chang, Vivian (Department: 2747)
Electrical audio signal processing systems and devices
Binaural and stereophonic
Stereo speaker arrangement
C381S017000
Reexamination Certificate
active
06181800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to simulated three-dimensional audio and, more particularly, to head related transfer functions.
2. Description of the Relevant Art
Head related transfer functions (HRTFs) are used to simulate positional three-dimensional (3-D) sound using fixed speaker locations. The shape of the human head, body and auditory system affect how the brain perceives the position of sound sources. An HRTF is a characterization of the human head, body and auditory system. The HRTF primarily accounts for the frequency response, frequency filtering, delays and reflections inherent in the human head, body and auditory system. By adjusting the frequency and delays of audio signals according to the HRTF, three-dimensional sound can be simulated from fixed speaker locations.
The HRTF for each individual is unique. As mentioned above, the HRTF characterizes the human head, body and auditory system. The HRTF is affected by the size and shape of the head, the size and shape of the pinnae, the characteristics of the ear canal, and the relationship of the shoulder to the ear. A unique HRTF can be calculated for each individual by performing detailed and time consuming measurements of the head, ear and body. The measurements taken for an individual are converted to a transfer function usable by a processing device to adjust the characteristics of audio signal outputs to individual speakers to simulate positional three-dimensional sound.
The detailed measurements required to determine the HRTF of an individual are time consuming and require special purpose equipment. Determining the HRTF of an individual by taking measurements is suitable for low volume special purpose applications where accuracy is important and cost is relatively unimportant. Taking individual measurements to determine an HRTF, however, is not suitable for high volume applications in which cost is a primary concern, e.g., computer games. Computer games may use HRTFs to simulate positional 3-D sound. Because the HRTF is different for each individual, determining the HRTF for each individual user of a computer game would require making detailed time consuming measurements of each user using special purpose equipment. This, of course, is not practical for widely distributed computer games.
A common alternative to individualized HRTFs in high volume applications is the use of a generalized HRTF. A generalized HRTF is an average HRTF. The generalized HRTF is an attempt to define an HRTF that is effective for a large percentage of the population. The generalized HRTF works well for some portion of the population, works poorly for some percentage of the population and may not work at all for some portion of the population. Therefore, a general HRTF is a marginal solution to the problem of selecting an effective HRTF for high volume applications.
Another solution for determining individual HRTFs in high volume applications is to define a finite number of lesser-generalized HRTFs. Each lesser-generalized HRTF consists of various combinations of head, pinnae, and auditory canal characteristics. These HRTs are referred to as lesser generalized HRTs because they are an average HRTF for a subset of the general population. Each lesser-generalized HRTF is suited for some portion of the population and therefore the combination of lesser-generalized HRTFs provide increased accuracy and performance for a wide range of the population. Unfortunately, it is difficult to determine which of the HRTFs is the most appropriate, or the best fit, for an individual user. Measurements of the head, ear and body typically must be made to determine the most appropriate HRTF for each user. Although these measurements may be less detailed and time consuming than the measurements to define an individualized HRTF, the measurements to determine the most appropriate HRTF are too detailed and time consuming to be practical for high volume applications. Additionally, the measurements may require specialized equipment not readily available to individual users.
What is desired is a system and method for accurately selecting or adjusting an HRTF for an individual without requiring detailed measurements of the individual.
SUMMARY OF THE INVENTION
The present invention contemplates an interactive method of selecting the best fit HRTF. A computer, or other device, starts with a generalized HRTF or one of a set of predetermined lesser-generalized HRTFs. The computer outputs audio signals that simulate sound at one or more positions using the generalized HRTF. User inputs to the computer indicates the perceived position of the sound. The computer determines the positional errors between the expected perceived position of the sound and the actual perceived position of the sound. The positional errors are used either to adjust the parameters of the generalized HRTF or select a new HRTF. This process of outputting audio signals, inputting the perceived position of the sound, calculating positional errors and selecting or adjusting the HRTF is repeated until the positional errors are within an acceptable range. The present invention thus advantageously provides a means of providing the mass market with a more accurate positional three-dimensional solution without performing detailed measurements requiring special purpose equipment.
Broadly speaking, the present invention contemplates a system for approximating a head related transfer function including a control unit, one or more speakers, and an input device. The control unit includes a storage device that stores one or more head related transfer functions. The speakers and input device are coupled to the control unit. The control unit outputs audio signals to the speakers or headphones using one of the stored head related transfer functions. An actual perceived position of the sound is input to the control unit via the input device. The control unit either adjusts one or more parameters of the head related transfer function or selects a new head related transfer function based on the actual perceived position of the sound.
The present invention further contemplates a method for interactive approximation of a head related transfer function including: selecting a first head related transfer function; outputting sound at one or more expected perceived positions using the first head related transfer function; receiving input from a user indicative of one or more actual perceived positions of the sound; and calculating positional errors between the one or more expected perceived positions of the sound and the one or more actual perceived positions of the sound. If the positional errors are within the acceptable error range, the first head related transfer function is used. If the positional errors are not within an acceptable error range, either one or more parameters of the first head related transfer function are adjusted or a new head related transfer function is selected. The above method is preferably iteratively repeated until the positional errors are in the acceptable error range.
REFERENCES:
patent: 5440639 (1995-08-01), Suzuki et al.
patent: 5495534 (1996-02-01), Inanaga et al.
patent: 5715317 (1998-02-01), Nakazawa
patent: 5742689 (1998-04-01), Tucker et al.
Advanced Micro Devices , Inc.
Chang Vivian
Conley Rose & Tayon PC
Hood Jeffrey C.
Stephenson Eric A.
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