78 results about "Ambisonics" patented technology

Representations of spatial audio scenes using higher-order Ambisonics HOA technology typically require a large number of coefficients per time instant. This data rate is too high for most practical applications that require real-time transmission of audio signals. According to the invention, the compression is carried out in spatial domain instead of HOA domain. The (N+1)² input HOA coefficients are transformed into (N+1)² equivalent signals in spatial domain, and the resulting (N+1)² time-domain signals are input to a bank of parallel perceptual codecs. At decoder side, the individual spatial-domain signals are decoded, and the spatial-domain coefficients are transformed back into HOA domain in order to recover the original HOA representation.

Immersive environments for teleconferencing, collaborative shared spaces and entertainment require spatial audio. Such environments may have non-ideal sound reproduction conditions (loudspeaker positioning, listener placement or listening room geometry) where wavefront-synthesis techniques, such as ambisonics, will not give listeners the correct audio spatialization. A method disclosed for generating a sound field from a spatialized original audio signal, wherein the original signal is configured to produce an optimal sound percept at one predetermined ideal location. A plurality of output signal components are generated, each for reproduction by one of an array of loudspeakers. Antiphase output components are attenuated such that their contribution to the spatial sound percept is reduced for locations other than the predetermined ideal location. Position components defining the location of a virtual sound source, normalized to the loudspeaker distance from the ideal location, can be adapted to generate a warped sound field by raising the position components to a power greater than unity, such that the virtual sound source is perceived by listeners in the region surrounded by the loudspeakers to be spaced from the loudspeaker.

Conventional audio compression technologies perform a standardized signal transformation, independent of the type of the content. Multi-channel signals are decomposed into their signal components, subsequently quantized and encoded. This is disadvantageous due to lack of knowledge on the characteristics of scene composition, especially for e.g. multi-channel audio or Higher-Order Ambisonics (HOA) content. An improved method for encoding pre-processed audio data comprises encoding the pre-processed audio data, and encoding auxiliary data that indicate the particular audio pre-processing. An improved method for decoding encoded audio data comprises determining that the encoded audio data had been pre-processed before encoding, decoding the audio data, extracting from received data information about the pre-processing, and post-processing the decoded audio data according to the extracted pre-processing information.

The invention discloses rendering sound field signals, such as Higher-Order Ambisonics (HOA), for arbitrary loudspeaker setups, where the rendering results in highly improved localization properties and is energy preserving. This is obtained by a new type of decode matrix for sound field data, and a new way to obtain the decode matrix. In a method for rendering an audio sound field representation for arbitrary spatial loudspeaker setups, the decode matrix for the rendering to a given arrangement of target loudspeakers is obtained by steps of obtaining a number of target speakers, their positions, positions of a spherical modeling grid and a HOA order, generating a mix matrix from the positions of the modeling grid and the positions of the speakers, generating a mode matrix from the positions of the spherical modeling grid and the HOA order, calculating a first decode matrix from the mix matrix and the mode matrix, and smoothing and scaling the first decode matrix with smoothing and scaling coefficients.

Higher Order Ambisonics represents three-dimensional sound independent of a specific loudspeaker set-up. However, transmission of an HOA representation results in a very high bit rate. Therefore compression with a fixed number of channels is used, in which directional and ambient signal components are processed differently. The ambient HOA component is represented by a minimum number of HOA coefficient sequences. The remaining channels contain either directional signals or additional coefficient sequences of the ambient HOA component, depending on what will result in optimum perceptual quality. This processing can change on a frame-by-frame basis.

Soundfield signals such as e.g. Ambisonics carry a representation of a desired sound field. The Ambisonics format is based on spherical harmonic decomposition of the soundfield, and Higher Order Ambisonics uses spherical harmonics of at least 2^nd order. However, commonly used loudspeaker setups are irregular and lead to problems in decoder design, A method for improved decoding an audio soundfield representation for audio playback comprises calculating a panning function using a geometrical method based on the positions of a plurality of loudspeakers and a plurality of source directions, calculating a mode matrix from the loudspeaker positions, calculating a pseudo-inverse mode matrix and decoding the audio soundfield representation. The decoding is based on a decode matrix that is obtained from the panning function and the pseudo-inverse mode matrix.

An advantage of Ambisonics representation is that the reproduction of the sound field can be adapted individually to nearly any given loudspeaker position arrangement. The invention allows systematic adaptation of the playback of spatial sound field-oriented audio to its linked visible objects, by applying space warping processing as disclosed in EP 11305845.7. The reference size (or the viewing angle from a reference listening position) of the screen used in the content production is encoded and transmitted as metadata together with the content, or the decoder knows the actual size of the target screen with respect to a fixed reference screen size. The decoder warps the sound field in such a manner that all sound objects in the direction of the screen are compressed or stretched according to the ratio of the size of the target screen and the size of the reference screen.

The invention discloses a method and a system for enhancing the sound field effect of a loudspeaker group in a regular tetrahedron structure. The method comprises the steps of enlarging the loudspeaker group in the regular tetrahedron structure to obtain four loudspeaker placing points and four virtual loudspeaker placing points; distributing four channels of collected first-order Ambisonics signals to four loudspeakers and four virtual loudspeakers; distributing signals of four virtual loudspeakers to three loudspeakers which are closest to virtual loudspeakers on the premise that the sound particle speed direction and the sound pressure intensity at a symmetrical central position of the regular tetrahedron structure are not changed; and canceling virtual loudspeakers. By the aid of the method and the system, the quality of the sound field can be reconstructed on the condition that loudspeakers of the same number are used.

There are two representations for Higher Order Ambisonics denoted HOA: spatial domain and coefficient domain. The invention generates from a coefficient domain representation a mixed spatial/coefficient domain representation, wherein the number of said HOA signals can be variable. A vector of coefficient domain signals is separated into a vector of coefficient domain signals having a constant number of HOA coefficients and a vector of coefficient domain signals having a variable number of HOA coefficients. The constant-number HOA coefficients vector is transformed to a corresponding spatial domain signal vector. In order to facilitate high-quality coding, without creating signal discontinuities the variable-number HOA coefficients vector of coefficient domain signals is adaptively normalised and multiplexed with the vector of spatial domain signals.

The perception of 3D sound positioning can be achieved using a 2D arrangement of speakers positioned around the listener. The disclosed techniques can enable listeners to perceive sounds as coming from above and/or below them, without the need for positioning speakers above and/or below the listener. In some embodiments, elevation information can be included in the X and Y horizontal components of the 2D ambisonics encoding. The X and Y components can be decoded using 2D ambisonics decoding. Suitable filtering may be performed on the decoded sound information to enhance the listener's perception of the elevation information encoded in the X and Y components.

A device includes a mixer configured to mix first ambisonic data and second ambisonic data to generate mixed ambisonic data. The first ambisonic data and the second ambisonic data correspond to different spatial orders. The device also includes ambisonic adjustment circuitry configured to adjust the mixed ambisonic data based on position data to generate an adjusted mixed ambisonic output.

The invention improves HOA sound field representation compression. The HOA representation is analysed for the presence of dominant sound sources and their directions are estimated. Then the HOA representation is decomposed into a number of dominant directional signals and a residual component. This residual component is transformed into the discrete spatial domain in order to obtain general plane wave functions at uniform sampling directions, which are predicted from the dominant directional signals. Finally, the prediction error is transformed back to the HOA domain and represents the residual ambient HOA component for which an order reduction is performed, followed by perceptual encoding of the dominant directional signals and the residual component.

The invention discloses an Ambisonics matching projection decoding method for irregular loudspeaker placements. The method comprises the following steps of 1) obtaining a spherical harmonics signal of a sound source according to the position of the sound source; obtaining a spherical harmonics signal of a loudspeaker according to the position of the loudspeaker; and 2) carrying out matching projection on the spherical harmonics signal of the sound source and the spherical harmonics signal of the loudspeaker to obtain a gain g of each loudspeaker. According to the method, the requirements of an Ambisonics sound reproduction system for the fixed positions of the loudspeakers are solved, and the reconstructed sound field is stable.

Spherical microphone arrays capture a three-dimensional sound field ( P ( © c , t )) for generating an Ambisonics representation A n m t , where the pressure distribution on the surface of the sphere is sampled by the capsules of the array. The impact of the microphones on the captured sound field is removed using the inverse microphone transfer function. The equalisation of the transfer function of the microphone array is a big problem because the reciprocal of the transfer function causes high gains for small values in the transfer function and these small values are affected by transducer noise. The invention estimates (73) the signal-to-noise ratio between the average sound field power and the noise power from the microphone array capsules, computes (74) the average spatial signal power at the point of origin for a diffuse sound field, and designs in the frequency domain the frequency response of the equalisation filter from the square root of the fraction of a given reference power and the simulated power at the point of origin.

Encoding of Higher Order Ambisonics (HOA) signals commonly results in high data rates. A method for low bit-rate encoding frames of an input HOA signal having coefficient sequences comprises computing (s110) a truncated HOA representation (C_T(k)), determining (s111) active coefficient sequences (1_c,Act(k)), estimating (s16) candidate directions (M_DIR(k)), dividing (s15) the input HOA signal into a plurality of frequency subbands (f₁, . . . , f_F), estimating (s161) for each of the frequency subbands a subset of candidate directions (M_DIR(k)) as active directions (M_DIR(k,f1), . . . , M_DIR(k,f_F)) and for each active direction a trajectory, computing (s17) for each frequency subband directional subband signals from the coefficient sequences of the frequency subband according to the active directions, calculating (s18) for each frequency subband a prediction matrix (A(k,f₁), . . . , A(k,f_F)) that can be used for pre-dicting the directional subband signals from the coefficient sequences of the frequency subband using the respective active coefficient sequences (Ic,_ACT(k)), and encoding (s19) the candidate directions, active directions, prediction matrices and truncated HOA representation.

Encoding of Higher Order Ambisonics (HOA) signals commonly results in high data rates. For data rate reduction, a method (100) for encoding direction information for frames of an input HOA signal comprises determining (s101) active candidate directions (I) among predefined global directions having global direction indices, dividing (s102) the input HOA signal into frequency subbands (II), determining (s103) for each frequency subband active subband directions among the active candidate directions, assigning (s104) a relative direction index to each direction per subband, assembling (s105) direction information for the frame, the direction information comprising the active candidate directions (I), for each subband and each active candidate direction a bit indicating whether or not the active candidate direction is an active subband direction for the respective frequency subband, and for each frequency subband the relative direction indices of active subband directions in the second set of subband directions, and transmitting (s106) the assembled direction information.

The invention is suited for improving a low bit rate compressed and decompressed Higher Order Ambisonics HOA signal representation of a sound field, wherein the decompression provides a spatially sparse decoded HOA representation and a set of indices of coefficient sequences of this representation. From reconstructed signals of the original HOA representation a number of modified phase spectra signals are created using de-correlation filters, which modified phase spectra signals are uncorrelated with the signals of said original representation. The modified phase spectra signals are mixed with each other using predetermined mixing parameters, in order to provide a replicated ambient HOA component. Finally the spatially sparse decoded HOA representation is enhanced with the replicated time domain HOA representation.

A method for compressing a HOA signal being an input HOA representation with input time frames (C(k)) of HOA coefficient sequences comprises spatial HOA encoding of the input time frames and subsequent perceptual encoding and source encoding. Each input time frame is decomposed (802) into a frame of predominant sound signals (X_PS(k−1)) and a frame of an ambient HOA component (C_AMB(k−1)). The ambient HOA component (C^˜_AMB(k−1)) comprises, in a layered mode, first HOA coefficient sequences of the input HOA representation (c_n(k−1)) in lower positions and second HOA coefficient sequences (c_AMB,n(k−1)) in remaining higher positions. The second HOA coefficient sequences are part of an HOA representation of a residual between the input HOA representation and the HOA representation of the predominant sound signals.