Since the 1920's, it has been known that the human auditory system treats direct and indirect sound differently in binaural perception. The time difference and delay as well as level difference of direct sound reaching each ear (also known as, interaural time difference and interaural level difference) provide cues that allow the listener to perceive distance and direction from a sound source. Audio typically also contains indirect sound created from repeated reflection and diffraction of sound within a space, which causes diffusion and uniform distribution of sound energy. For example, a diffuse sound field is typical of a gymnasium, swimming pool and interior spaces with many reflecting surfaces and low sound absorption, and also is typical of outdoor locations with sound coming from many directions (such as the canyon effect of an urban street lined with high-rise buildings).
When audio is recorded, both direct and indirect sound typically is captured in the recording. When played back on a conventional loudspeaker system, the hardware makes no attempt to distinguish the direct and indirect sound in the recording. With a very few exceptions, loudspeakers have had fixed ratios of direct-to-indirect radiation that depend on both specific room acoustics and the loudspeaker design. This can create a false perception of distance and direction for the indirect sound played back from a loudspeaker, and conversely fails to provide accurate perceptual cues for direct sound. The conventional loudspeaker system therefore fails to provide a perceptually accurate reproduction of the original audio.
The following Detailed Description concerns an array loudspeaker that provides direct and indirect sound radiating from a same set of drivers (i.e., electro-acoustic transducers) in an array configuration. The loudspeaker includes a digital signal processor-based (DSP) control system to individually control sound radiated from the drivers. Using beam-forming or steering techniques, a DSP-based control system varies the phase or delay of a direct sound signal radiating from individual drivers of the array to create a directed beam or wavefront. Simultaneously, the control system can cause the driver array to radiate an indirect sound signal in a pattern from the drivers that reduces time waveform and envelope correlation at the ear. This creates a perceptually diffuse sound field, which is characterized by having very low spatial correlation. In this way, the loudspeaker can create any arbitrary combination of directed beams or wavefronts, and indirect sound radiation. For example, the loudspeaker could direct a beam at an individual in the room, a general beam at the whole room, and provide a diffuse, enveloping ambience, simultaneously.
In one implementation, the array can be configured as a linear, uniformly spaced arrangement of drivers. More advantageously, another implementation of the array loudspeaker has the drivers configured as a linear array with octave array spacing. Such configuration as an octave array allows the use of fewer drivers to maintain the same bandwidth relative to a uniform array. The term bandwidth in this context refers to the ratio of frequencies of the direct sound radiation that can be handled with the array. Rather than using all drivers exclusively in a beam-forming operation, various subsets of the octave array drivers at different spacings are used for different bands of frequencies. For example, all drivers may be used to radiate the low frequencies of the direct sound signal, and sets of successively fewer, more-closely spaced drivers to radiate in higher frequency bands. This creates a pseudo-constant beamwidth. Additionally, by dithering the delays of the indirect sound radiated from the drivers, the array can simultaneously create a perceptually diffuse sound field.
This array loudspeaker can be used in a variety of applications to provide a more effective “overlay” of the desired playback acoustics over the actual room acoustics than would be possible using conventional loudspeaker designs. For example, two such array loudspeakers can be paired for a personal (single listener) experience. For such personal reproduction applications, the pair of array loudspeakers can provide an enveloping experience that perceptually recreates the direct and indirect sounds of the original audio environment, without severely limiting listening position or head angle.
For applications involving a larger group of listeners, a number of these array loudspeakers can be arranged in a surround configuration (e.g., a 5, 5.1 or 5.2 surround configuration) to provide a much better sense of inclusion in an auditory environment that better reproduces perception of direct and indirect sounds of the original environment.
In a gaming application, these array loudspeakers arranged in a personal or surround configuration can simply the synthesis of an audio environment containing direct and indirect sound components surrounding the listener(s). With use of such array loudspeakers, the game application is able to vary the direct/indirect ratio in the audio signal from each array loudspeaker, so as to provide direction, distance and depth effects that are much better than those available from conventional direct radiator loudspeaker types.
This Summary is provided to introduce a selection of concepts in a simplified form that is further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. Additional features and advantages of the invention will be made apparent from the following detailed description of embodiments that proceeds with reference to the accompanying drawings.
The following description presents variations of an array loudspeaker that produces direct sound and indirect sound radiated from a same array of drivers. Using digital signal processing techniques, a first or direct audio signal input is processed to radiate as a directed beam from the loudspeaker's driver array. The direct sound signal also can be processed to radiate from the driver array as a directed planar or spherical wavefront. In addition to radiating such direct sound, digital signal processing also is applied to a second or indirect audio signal input to have different phase and amplitude when radiated from each driver of the driver array, so as to be substantially decorrelated in amplitude and envelope at the listener's ears. This creates a soundfield that presents auditory cues that appear as indirect or diffuse sound (i.e., having very low spatial correlation) to the human auditory system. With a set of multiple such array loudspeakers producing direct and indirect sound (e.g., as a stereo pair or surround set arrangement) in a listening room or other space, it is possible to create illusions of depth, distance and direction, with a loudspeaker design that need not occupy a substantial room volume.
With reference to
The direct and indirect audio signals input to the array loudspeaker can originate in a variety of ways. For applications like computer video games, the game application can separately synthesize the audio signals from direct sources in the virtual game environment, as well as synthesize an indirect audio signal for the diffuse sound for the virtual space of the game environment. The direction parameter data likewise is calculated from the direct sound sources within the game environment.
For recorded sound, the direct and indirect audio signals can be produced by analyzing the stereo channels of a sound recording to identify perceptual soundfield imaging cues characteristic of direct sound, such as by applying an envelope detection analysis in critical bands as described by Johnston, U.S. Pat. No. 7,027,601. Further, the direct and indirect sound signals can be captured even more accurately at recording by using an arrangement of directional microphones, which may be a stereo pair or more preferably in some applications can be arranged on a sphere as described by Johnston et al., U.S. Pat. No. 6,845,163. Similarly, the direction parameter data for the direct sound is derived by analyzing the recorded microphone channels to identify direction from which the identified direct sound originated.
The driver array 130 of the array loudspeaker 100 includes a plurality of drivers arranged in an array configuration. Preferably, each of the drivers forming the array is identical in size, and enclosure. Further, due to the Nyquist principle, the center-to-center spacing of the drivers can be no more than one half of the shortest wavelength (highest frequency of sound) apart for the controller to be able to steer or control the direction of the direct sound beam or wavefront radiated from the array without aliasing effects. The spacing of drivers in the array therefore determines the maximum frequency of the direct sound radiation from the array loudspeaker. On the other hand, lower frequencies require more energy to produce with a given size of driver. The choice of driver size and spacing between drivers therefore practically limit the range of frequencies that can be produced by the array loudspeaker.
In one embodiment, the drivers 131-135 forming the driver array 130 are arranged in a uniform spacing configuration as illustrated in
In a more preferred embodiment, the drivers 131-135 that form the driver array 130 are instead arranged with octave array spacing as illustrated in
With the octave array configuration, each separate uniformly spaced subset of drivers can be used for a different range or band of frequencies. For example, the drivers forming the center 5 elements of the illustrated octave array are used for the highest frequency band, while successive more widely spaced subsets are used for successively lower frequency bands (the maximum frequency of each band being half the maximum frequency of the previous band). In this way, the driver array 130 with octave array configuration 300 is able to cover a much broader range of frequencies using fewer drivers compared to the uniformly spaced array. In general, the octave array configuration achieves a bandwidth of approximately 2^((N−1)/2), for N elements. For an example array having 11 elements (such as that illustrated in
One suitable choice of driver size is to use an array of one-inch diameter drivers. Allowing for enclosure walls separating the driver enclosures in the array, this choice of driver size permits a closest center-to-center driver spacing of approximately one and one third inches, which allows for a maximum high frequency of approximately 10 kHz. However, depending on the desired application, a smaller or larger driver size can be chosen to provide a different maximum frequency of the direct sound beam or wavefront. With only 11-elements in an octave array configuration for example, the driver array using this driver size can radiate sound over a frequency range of less than 500 Hz to over 10 kHz.
Although the driver array 130 in the above embodiments has drivers configured as a linear array in a single dimension, alternative implementations can use non-linear arrangements of the drivers (e.g., on a curve), such as to aid in creating a spherical wavefront for the directional sound. Additionally, alternative embodiments can use a two dimensional arrangement of the drivers. For example, the array loudspeaker can include a second octave array at a perpendicular angle to the first octave array (or alternatively two or more additional octave arrays offset at uniform or non-uniform angles from a first, horizontal octave array).
The loudspeaker controller 110 includes a digital signal processor (DSP) 410 for processing the direct and indirect audio signal inputs 120-122 to produce output audio signals for each of the drivers 131-133 in the driver array 130. The illustrated implementation of the loudspeaker controller includes various interfaces that can act as the audio and direction data inputs 120-122, including a digital audio interface 420 (such as, a SPDIF (Sony/Philips Digital Interface Format) format interface), a serial data interface 421 (such as, a universal serial bus (USB) interface), and an analog-to-digital converter 440. Alternative implementations of the loudspeaker controller can provide only analog audio inputs, only digital audio inputs, or both digital and analog inputs. Further, alternative loudspeaker controller implementations can use various other interface formats or standards.
The loudspeaker controller 110 also includes random access memory (RAM) 450 and read only memory (ROM) 451. The ROM 451 stores firmware and audio processing instructions for the digital signal processor. The RAM 450 is used by the digital signal processor 410 for temporary storage of data during audio processing. The RAM 450 in the illustrated embodiment is a synchronous dynamic random access memory (SDRAM), although other memory technologies alternatively can be used.
The loudspeaker controller 110 further includes a bank of digital-to-analog converters for producing the audio signal outputs to the individual drivers 131-133 of the driver array 130. In one implementation, the loudspeaker controller has 16 channels of digital-to-analog converter outputs, which is sufficient to provide the output channels for a driver array configured as the eleven element octave array illustrated in
The digital signal processor 410 creates a directed beam or spherical wavefront by modifying the phase, amplitude and/or delay of the direct audio signal on individual driver output channels 511-512 using a set of beam/wavefront-forming filters 521-522, which may be implemented in the digital signal processor programming as digital all-pass finite impulse response (FIR) filters. Although only two driver channels 511-512 are shown in
In some embodiments, the array loudspeaker can operate to create a pseudo-constant sound beamwidth by radiating sound from all drivers of the driver array at low frequencies and progressively fewer drivers at higher frequency ranges. For a given size driver, the intensity of sound produced by the driver diminishes as the frequency of the audio signal goes lower. In other words, a progressively higher power signal would be required to produce the same sound intensity at a progressively lower frequency with the same driver. The loudspeaker array can compensate for this effect by radiating the signal from more drivers of the array at its lowest frequencies, and using progressively fewer drivers at higher frequencies so as to produce a pseudo-constant beamwidth. For example, as described above for the octave array configuration 300 (
In addition to creating a directed beam and/or wavefront, the array loudspeaker 100 can simultaneously create diffuse sound output based on the separate indirect sound input, and can vary the ratio of direct to indirect sound in a way that more accurately simulates an overlay of a desired soundfield on the listening space. The loudspeaker controller 110 creates a diffuse sound field using digital signal processing to modify the phase and amplitude of the indirect sound signal such that the pattern of the indirect sounds has reduced time waveform and envelope correlation. In one implementation, the digital signal processor use a set of digital filters 531-532 to modify the phase and amplitude of the indirect sound signal for each of the individual driver channels 511-512. These filters also can be implemented as all-pass, finite impulse response filters. The filters 511-512 dither the delay of the indirect signal in the driver channels, so that the indirect signal radiated by each individual driver is different from the direct signal radiated from all other drivers. In one embodiment, each driver channel is assigned a different prime number, and the indirect audio signal is delayed in relation to the prime number assigned to the driver channel. The prime numbers assigned to the driver channels are chosen so that the indirect audio signal delay is on average the same across the drivers. This radiates the indirect audio signal from the driver array in a pattern with reduced time waveform and envelope correlation creating a sensation of diffuse sound for the listener.
Finally, for each driver channel 511-512, the digital signal processor 410 sums the direct audio signal and indirect audio signal as shown by summation blocks 541-542 to produce the audio output radiated by the individual drivers 131-132 of the array.
In view of the many possible embodiments to which the principles of our invention may be applied, we claim as our invention all such embodiments as may come within the scope and spirit of the following claims and equivalents thereto.
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