HK1170101B - Audio system and audio signal processing system - Google Patents

Abstract

An audio system including a rendering processor for separately rendering a dialogue channel and a center music channel. The audio system may include circuitry for extracting one or both of the dialogue channel or the center music channel from program material that does not include both a dialogue channel and a center music channel. The dialogue channel and the center music channel may be radiated with different radiation patterns.

Description

Audio system and audio signal processing system

Technical Field

This specification describes a multi-channel audio system having a so-called "center channel".

Disclosure of Invention

In one aspect, an audio system includes a rendering processor for separately rendering a dialogue channel and a center music channel. The audio system may further comprise a channel extractor for extracting at least one of the dialogue channel and the center music channel from program material that does not include both the dialogue channel and the center music channel. The channel extractor may include circuitry for extracting the dialogue channel and the center music channel from program material that does not include either of the dialogue channel and the center music channel. The rendering processor may further include circuitry for processing the dialogue channel audio signal and the center music channel audio signal such that the directional array radiates the center dialogue channel and the center music channel with different radiation patterns. The same directional array may radiate a dialogue channel and a center music channel. Different elements of the same directional array may radiate a dialogue channel and a center music channel. In a frequency range of the dialogue channel radiation pattern, an internal angle of a direction having a sound pressure level within-6 dB of a highest sound pressure level in any direction is less than 120 degrees, and in at least a part of the frequency range of the center music channel radiation pattern, an internal angle of a direction having a sound pressure level within-6 dB of a highest sound pressure level in any direction is greater than 120 degrees. The difference between the maximum sound pressure level in any direction in the frequency range and the minimum sound pressure level in any direction in the frequency range may be greater than-6 dB for a dialogue channel radiation pattern and between 0dB and-6 dB for a center music channel radiation pattern. The rendering processor may render the dialogue channel and the center music channel to different speakers. The rendering processor may combine the center music channel with the left channel or the right channel or both.

In another aspect, an audio signal processing system includes a discrete center channel input and signal processing circuitry for creating a center music channel. The signal processing circuitry may include circuitry for processing channels other than the discrete center channel to create a center music channel. The signal processing circuitry may include circuitry for processing the discrete center channel and other audio channels to create a center music channel. The audio signal processing system may further comprise circuitry for providing the discrete center channel to the first speaker and the center music channel to the second speaker.

In another aspect, an audio processing system includes a channel extractor for extracting at least one of a dialogue channel and a center music channel from program material that does not include both the dialogue channel and the center music channel. The channel extractor may include circuitry for extracting the dialogue channel and the center music channel from program material that does not include either of the dialogue channel and the center music channel.

Drawings

FIG. 1 is a block diagram of an audio system;

FIG. 2 is a block diagram of an audio system including a center channel extractor;

FIG. 3 is a block diagram of an audio system including a center music channel extractor and a dialogue channel extractor;

FIG. 4 is a block diagram of an audio system including a dialogue channel extractor;

FIG. 5 is a block diagram of an audio system lacking a dedicated center channel playback device;

FIG. 6 is a polar plot of acoustic radiation patterns;

fig. 7 to 10 are schematic views of a channel extraction processor, a channel rendering processor, and a playback apparatus; and

fig. 11A-11D are polar plots of radiation patterns for a dialogue channel and a center music channel.

Detailed Description

Although the elements of the several views of the drawing are illustrated and described as discrete elements in a block diagram and referred to as "circuitry," unless indicated to the contrary, the elements may be implemented as one or a combination of analog circuitry, digital circuitry, or one or more microprocessors executing software instructions. The software instructions may include Digital Signal Processing (DSP) instructions. Unless indicated to the contrary, the signal lines may be embodied as separate analog or digital signal lines, a single separate digital signal line with appropriate signal processing for processing the separate audio signal streams, or elements of a wireless communication system. Unless indicated to the contrary, the audio signal may be encoded in digital or analog form. For convenience, the "radiated sound wave corresponding to the channel x" will be expressed as "radiated channel x". The "speakers" or "playback devices" are not limited to devices having a single acoustic driver. The speaker or playback device may include more than one acoustic driver and may include some or all of the plurality of acoustic drivers in a common housing, if appropriate with signal processing. With appropriate signal processing, different combinations of acoustic drivers in a common enclosure may constitute different speakers or playback devices.

Multiple multi-channel audio systems may process or play back the center channel. The center channel may be a separate channel present in the sound source material or the center channel may be extracted from other channels, such as a left channel and a right channel.

The desired sound image of the center channel may vary depending on the content of the center channel. For example, if the program content includes a spoken dialog whose intended apparent sound source is on the screen or monitor, it is often desirable for the sound image to be "tight" and clearly on the screen. If the program content is music, it is generally desirable that the apparent sound source be more vague and diffuse.

A compact on-screen image is usually associated with a spoken dialog, usually a moving picture or a video reproduction of a moving picture. For this reason, the center channel associated with the compact on-screen imagery will be referred to herein as a "dialogue channel," which should be understood as a dialogue channel that may include non-dialogue elements and in some instances dialogue may be present in other channels (e.g., if an intended apparent sound source is off-screen) and also understood that there may be instances when a more diffuse center imagery is desired (e.g., a voice-over).

More diffuse sound images are often associated with music, especially musical instruments or string music. For this reason, the center channel associated with the diffuse image will be referred to herein as the "center music channel," which should be understood as the music channel may include dialog and also as instances where a more compact on-screen sound image for music audio is desired.

The dialogue channel and the center music channel may also vary in frequency content. The frequency content of the dialogue channel is typically in the voice frequency spectrum band (e.g., 150Hz to 5kHz), while the frequency content of the center music channel may range in a wider frequency spectrum band (e.g., 50Hz to 9 kHz).

If the sound source material does not have a center channel (dialogue or music), but the rendering or playback system does have the ability to radiate the center channel, the rendering or playback system may extract the center channel from the sound source audio signal. Extraction can be accomplished by a variety of methods. In one method, voice content is extracted such that the center channel is a dialogue channel, and the voice content is played back by a center channel playback device. One simple method of extracting the vocal tract is to use a band pass filter to extract the spectral portion of the input signal in the vocal band. Other more sophisticated methods may include analyzing correlations between input channels or detecting characteristic patterns of speech. In another method for extracting a center channel, the content of at least two directional channels is processed to form a new directional channel. For example, the left front channel and the right front channel may be processed to form a new left front channel, a new right front channel, and a center front channel.

Treating the dialogue channel as a center music channel or vice versa may have undesirable results. If the dialogue channel is treated as a center music channel, the sound may appear diffuse rather than the desired compact on-screen image and the words may not be as understandable as desired. If the center music channel is treated as a dialogue channel, the sound image may appear narrower and more direct than desired, and the frequency response may be undesirable.

Referring to fig. 1, an audio system 10 is shown. The audio system comprises a plurality of input channels 11 (represented by lines) for receiving audio signals from an audio signal source. The audio system may include a channel extraction processor 12 and a channel rendering processor 14. The audio system also includes a plurality of playback devices that may include a dialogue playback device 16, a center music channel playback device 18, and other playback devices 20.

As will be described in more detail below, in operation, the channel extraction processor 12 extracts additional channels from the input channels 11 that may not be included in the input channels. The additional channels may include a dialogue channel 22, a center music channel 24 and other channels 25. The channel rendering processor 14 prepares the audio signals in the audio channels for reproduction by the playback devices 16, 18, 20. The processing performed by the rendering processor 14 may include amplification, equalization, and other audio signal processing (such as spatial enhancement processing).

In fig. 1 and subsequent figures, the channels are represented by discontinuous lines. In a practical embodiment, multiple input channels may be input through a single input terminal or transmitted through a single signal path, wherein the signal processing is adapted to separate the multiple input channels from the single input signal stream. Similarly, the channels represented by lines 22, 24 and 25 may be a single audio signal stream with appropriate signal processing for separately processing multiple input channels. Many audio systems have a separate bass or Low Frequency Effects (LFE) channel that may include a combined bass portion of multiple channels and may be radiated by a separate low frequency loudspeaker, such as a woofer or subwoofer. The audio system 10 may have low frequency or LFE channels and may also have woofers or sub-woofers, but for convenience they are not shown in this view. As will be described below, the playback devices 16, 18, 20 may be conventional speakers or may be some other type of device (such as a directional array). The playback devices may be separate and individual as shown or may share some or all of the elements (such as directional array 40CD of fig. 9 or directional array 42 of fig. 10).

The channel extraction processor 14 and the channel rendering processor may comprise discrete analog or digital circuit elements, but are most efficiently performed by a Digital Signal Processor (DSP) that performs signal processing operations on the digitally encoded audio signal.

Fig. 2 shows in more detail the audio system with the channel extraction processor 12 (shown more specifically with the center channel extractor 26). In the system of fig. 2, there are five input channels: a center dialogue channel C, a left channel L, a right channel R, a left surround channel LS, and a right surround channel RS. The terminals for the L channel and the R channel are coupled to a center channel extractor 26 that is coupled to the center music channel playback device 18 and to the L channel playback device 20L and the R channel playback device 20R through the channel rendering processor 14. In this and subsequent figures, a prime (') symbol indicates the output of the channel extraction processor 14. The content of the channels produced by the extractor may be substantially the same as or may be different from the content of the corresponding input channels. For example, the content of the left channel L' produced by the channel extractor may be different from the content of the left input channel L.

In operation, the center channel extractor 26 processes the L and R input channels to provide a center music channel C ' and left and right channels (L ' and R '). The playback device 18 then radiates the center music channel.

The center music channel extractor 26 is typically a DSP that performs signal processing operations on the digitally encoded audio signal. Methods of extracting a center music channel are described in published U.S. patent application 2005/0271215 or U.S. patent 7,016,051, which are incorporated herein by reference in their entirety.

In the audio system of fig. 3, the sound source material has only two input channels L and R. The center channel extractor 26 (coupled to the center music channel playback device 18, the left playback device 20L, and the right playback device 20R via the channel rendering processor 14), the dialogue channel extractor 28 (coupled to the dialogue playback device 16), and the surround channel extractor 30 (coupled to the surround playback devices 20LS and 20RS via the rendering processor 14) of fig. 2 are coupled to the input channels L and R.

In operation, the center channel extractor 26 processes the L and R input channels to provide a center music channel C' and left and right channels. The left and right channels (L ' and R ') produced by the channel extractor may be different from the L and R input channels as indicated by the prime (') indicators. The center music channel playback device 18 then radiates the center music channel. The dialogue channel extractor 28 processes the L and R channels to provide a dialogue channel D' which is then radiated by the dialogue playback device 16. Surround channel extractor 30 processes the L and R channels to provide left and right surround channels LS and RS, which are then radiated by surround playback devices 20LS and 20RS, respectively.

The center music channel extractor 26, the dialogue channel extractor 28 and the surround channel extractor 30 are typically DSPs that perform signal processing operations on digitally encoded audio signals. A method of extracting a center music channel is described in us patent 7,016,501. A method of extracting a dialogue channel is described in us patent 6,928,169. Methods of extracting surround channels are described in U.S. patent 6,928,169, U.S. patent 7,016,501, or U.S. patent application 2005/0271215, which are incorporated herein by reference in their entirety. Another method of extracting surround channels is ProLogic, Dolby Laboratories, Inc., san Francisco, CalifProvided is a system.

The audio system of fig. 4 has a center music input channel C, but no dialogue channel. The dialogue channel extractor 28 is coupled to the C channel input terminal and the dialogue playback device 16 and the center music channel playback device 18 through the channel rendering processor 14.

In operation, the dialogue channel extractor 28 extracts a dialogue channel D' from the center music channel and other channels, if appropriate. The dialogue playback device 16 then radiates the dialogue channel. In other embodiments, the input to the center channel extractor may also include other input channels (such as L and R channels).

The audio system of fig. 5 does not have the center music channel playback device 18 of the previous figures. The audio system of fig. 5 may have the input channels and channel extraction processors of any of the front maps and may omit them from this view. The audio system of fig. 5 may also include left surround and right surround channels, also not shown in this view. The channel rendering processor 14 of fig. 5 may include a spatial enhancer 32 coupled to the center music channel 24. The center music channel signal is summed with the left channel at summer 34 and summed with the right channel at summer 36 (by optional spatial enhancer 32 if optional spatial enhancer 32 is present) such that the center channel is radiated by left channel acoustic driver 20L and right channel acoustic driver 20R. The channel rendering processor 14 renders the center channel by rendering circuitry that is more suited to music than dialog and radiates the center channel by acoustic drivers that are more suited to music than dialog, without the need for separate center channel rendering circuitry and separate center music channel acoustic drivers.

Spatial enhancer 32 and summers 34 and 36 are typically implemented in a DSP that performs signal processing operations on digitally encoded audio signals.

The sound image may be enhanced by using directional loudspeakers, such as directional arrays. Directional loudspeakers are loudspeakers with a radiation pattern in which more acoustic energy is radiated in some directions than in others. Directions radiating relatively more acoustic energy, such as directions in which the sound pressure level is within 6dB (preferably between-6 dB and-4 dB and ideally between-4 dB and-0 dB) of the maximum Sound Pressure Level (SPL) at a point equidistant from the directional speaker in any direction, will be referred to as "high radiation directions". Directions radiating less acoustic energy (e.g., directions in which SPL is at least a level of-6 dB (preferably between-6 dB and-12 dB and ideally at a level that drops more than 12dB, e.g., -20dB) relative to a maximum of points equidistant from the directional loudspeaker in any direction) will be referred to as "low radiation directions".

The directional characteristic of a loudspeaker is typically displayed as a polar plot (such as the polar plot of fig. 6). The radiation pattern of the loudspeaker is plotted in a set of concentric rings. The outermost ring represents the maximum sound pressure level in any direction. The next outermost ring represents a certain level of sound pressure level reduction (e.g., -6 dB). The next outermost ring represents a more reduced sound pressure level (e.g., -12dB), and so on. One way to express the directionality of a loudspeaker is the interior angle between the-6 dB points on either side of the direction of maximum sound pressure level in any direction. For example, in FIG. 6, radiation pattern 112 has an interior angle less than interior angle θ of radiation pattern 114Radiation pattern 112 is therefore considered to be more directional than radiation pattern 114. Radiation patterns such as pattern 114 in which the interior angle approaches 180 degrees may be described as "non-directional". A radiation pattern such as pattern 116 within-6 dB of the maximum of radiation in any direction in all directions may be described as "omnidirectional". The directional characteristic may also be classified as more directional by the difference between the maximum and minimum sound pressure levels. For example, in radiation pattern 112, the difference between the maximum and minimum sound pressure levels is-18 dB, which would be characterized as being more directional than radiation pattern 114 in which the difference between the maximum and minimum sound pressure levels is-6 dB, and radiation pattern 114 would be characterized as being more directional than radiation pattern 116 in which the difference between the maximum and minimum sound pressure levels is less than-6 dB.

Radiating the dialogue channel directly from the directional loudspeaker towards the listener makes the sound image compact and makes the apparent source of the sound clearly in the vicinity of the listener. Radiating the music channel from directional loudspeakers, but not directly at the listener, so that the amplitude of the reflected radiation is similar to or even higher than the amplitude of the direct radiation, may make the sound image more diffuse, as if the center music channel were radiated with less directionality or from non-directional loudspeakers.

One simple way to achieve directionality is to achieve directionality through the dimensions of the speaker. The speaker tends to become directional at wavelengths close to and shorter than the diameter of the radiating surface of the speaker. However, this may be impractical because directionally radiating the conversation channel may require a large-surfaced speaker to achieve directionality in the voice band.

Another way to achieve directionality is through the mechanical configuration of the speaker (e.g., through the use of an acoustic lens, baffle, or horn).

A more efficient and versatile way to achieve directionality is by using a directional array to achieve directionality. The directional array is a directional loudspeaker having a plurality of sources of acoustic energy. Directional arrays are discussed in more detail in U.S. patent No. 5,870,484, which is incorporated herein by reference in its entirety. In a directional array, sound pressure waves radiated by an acoustic energy source interfere destructively over a range of frequencies in which the corresponding wavelengths are large relative to the spacing of the energy sources, so that the array radiates more or less energy in different directions depending on the degree of destructive interference that occurs. Directional arrays are advantageous because the degree of directionality can be controlled electronically and because a single directional array can radiate two or more channels and can radiate two or more channels with different degrees of directionality. In addition, the acoustic driver may be a component of more than one array.

In some figures, the directional loudspeaker is shown diagrammatically as having two conical acoustic drivers. The directional loudspeaker may be some type of directional loudspeaker other than a multi-element loudspeaker. The acoustic driver may be of a type other than the cone type (e.g., dome type or flat plate type). The directional array has at least two sources of acoustic energy and may have more than two sources of acoustic energy. Increasing the number of acoustic energy sources increases control over the directional loudspeaker radiation pattern, for example, by allowing control of the radiation pattern in more than one plane. The directional loudspeakers in the figures show the location of the loudspeakers but not necessarily the number or orientation of the acoustic energy sources.

Fig. 7-10 depict embodiments of the audio system of some of the previous figures having a feedback system including directional speakers. Fig. 7-10 show the spatial relationship of the speakers to the listener 38 and also indicate which speakers radiate which channels and the degree of directionality of the radiated channels. A radiation pattern that is more directional than other radiation patterns in the same figure will be indicated by one arrow pointing in the direction of maximum radiation that is much longer and thicker than the other arrows. A less directional pattern will be indicated by the arrow pointing in the direction of maximum radiation being longer and thicker by a smaller amount than the other arrows. Fig. 7-10 may include other channels, such as surround channels, but surround channels may not be shown. Details of the channel extraction processor 12 and the channel rendering processor 14 are not shown in these views, nor are details of the input channels shown.

The radiation pattern of the directional array can be controlled by varying the amplitude and phase of the signal fed to each array element. In addition, the amplitude and phase of each element can be controlled independently at each frequency. The radiation pattern can also be controlled by the characteristics of the transducer and varying array geometry.

The audio system of fig. 7 includes directional arrays 40L, 40R, 40C and 40D coupled to the channel rendering processor 14.

The audio system of fig. 7 is suitable for use with the audio system of any of fig. 1-4 that produces a dialogue channel D ', a center music channel C', and left and right channels L 'and R', respectively. The dialogue channel D' is radiated in a highly directional radiation pattern from a directional array 40D approximately directly in front of the listener 38. The directional array 40C, which is approximately directly in front of the speaker, radiates the center music channel C' with a radiation pattern that is less directional than the radiation pattern of the directional array 40D. The directional arrays on the left and right sides, respectively, of listener 38 radiate the left channel L 'and right channel R' with radiation patterns that are approximately equally directional as the radiation patterns of directional array 40C.

The audio system of fig. 8 includes directional arrays 40L, 40R, and 40CD coupled to the channel rendering processor 14. The audio system of fig. 8 is also suitable for use with the audio system of one of fig. 1-4. The audio system of fig. 8 operates similarly to the audio system of fig. 7, but radiates both the dialogue channel D 'and the center music channel C' with different degrees of directionality.

The audio system of fig. 9 includes the channel rendering processor of fig. 5. Left directional array 40L, right directional array 40R, and dialogue directional array 40D are coupled to channel rendering processor 14. The left directional array 40L radiates the left channel L 'and the center channel left portion C' [ L ]. The right directional array 40R radiates a right channel R 'and a center channel right portion C' [ R ] (which may be the same as or different from the center channel left portion). Dialog steering array 40D radiates dialog channel D' with a higher degree of directionality than other channels radiated from steering arrays 40L and 40R.

In the audio system of fig. 10, the channel rendering processor 14 is coupled to an array 42 comprising a plurality of (in this example, 7) acoustic drivers. The directional array, which includes subsets of acoustic drivers, radiates the audio signals in the channels L ', R', C ', D', LS ', and RS' (and C '[ L ] and C' [ R ]) (if present) with varying degrees of directionality. In one embodiment, the center music channel and the dialogue channel are radiated by three center acoustic drivers 44 and also by a tweeter that is not part of the directional array.

For example, in fig. 11A, in the frequency band of 250Hz to 660Hz, the interior angle of the high radiation direction (within-6 dB of maximum radiation in any direction) of the dialogue channel radiation pattern 120 is about 90 degrees, while the interior angle of the high radiation direction of the music center channel radiation pattern 122 is about 180 degrees. The difference between the maximum and minimum sound pressure levels in any direction is-12 dB for the dialogue channel 120. The difference between the maximum sound pressure levels in any direction is-6 dB for the music center channel 122. The dialogue channel radiation pattern 120 is thus more directional in this frequency range than the radiation pattern 122 of the music center channel.

In fig. 11B, for the 820Hz third octave (octave), the interior angle of the high radiation direction is about 120 degrees for the dialogue channel radiation pattern 120 and about 180 degrees for the music center channel radiation pattern 122. The difference between the maximum and minimum sound pressure levels in any direction for the vocal tract radiation patterns 120 is approximately-9 dB, while the difference between the maximum and minimum sound pressure levels for the musical centre vocal tract radiation patterns 122 is approximately-6 dB. The dialogue channel radiation pattern 120 is thus also more directional in this frequency range than the radiation pattern 122 of the music center channel.

In fig. 11C, for the third octave of 1kHz, the interior angle of the high radiation direction is about 130 degrees for the dialogue channel radiation pattern 120, and the radiation pattern 122 of the music center channel is substantially omnidirectional, so the dialogue channel radiation pattern 120 is more directional than the radiation pattern 122 of the music center channel.

In fig. 11D, the radiation patterns of both the dialogue channel radiation pattern 120 and the music center channel are substantially omnidirectional for the 2kHz third octave. The difference between the maximum and minimum sound pressure levels is about-3 dB for the dialogue channel radiation pattern 120 and about-1 dB for the music center channel radiation pattern, and thus the dialogue channel radiation pattern is slightly more directional than the music center channel radiation pattern.

Since the radiation pattern of the dialogue channel radiation pattern 120 is more directional than the radiation pattern 122 of the music center channel in all frequency ranges shown in fig. 11A, 11B, 11C, and 11D, it is more directional than the radiation pattern 122 of the music center channel.

Those skilled in the art may now make numerous uses and modifications of the specific apparatus and techniques disclosed herein without departing from the inventive concepts. The invention is thus to be understood as embracing each and every novel feature and novel combination of features disclosed herein and limited only by the spirit and scope of the appended claims.

Claims (11)

1. An audio system, comprising:

a rendering processor for separately rendering the dialogue channel and the center music channel;

the rendering processor further comprises circuitry for processing the dialogue channel audio signal and the center music channel audio signal such that the directional array radiates the dialogue channel and the center music channel with different radiation patterns;

wherein the dialogue channel and the center music channel are radiated by the same directional array.

2. The audio system of claim 1, further comprising: a channel extractor for extracting at least one of the dialogue channel and the center music channel from program material that does not include both the dialogue channel and the center music channel.

3. The audio system of claim 2, wherein the channel extractor comprises circuitry for extracting the dialogue channel and the center music channel from program material that does not include either of the dialogue channel and the center music channel.

4. The audio system of claim 1 wherein the dialogue channel and the center music channel are radiated by different elements of the same directional array.

5. The audio system of claim 1, wherein in a frequency range of the dialogue channel radiation pattern, an interior angle of a direction having a sound pressure level within-6 dB of a highest sound pressure level in any direction is less than 120 degrees, and wherein in at least a portion of the frequency range of the center music channel radiation pattern, an interior angle of a direction having a sound pressure level within-6 dB of a highest sound pressure level in any direction is greater than 120 degrees.

6. An audio system, comprising:

a rendering processor for separately rendering the dialogue channel and the center music channel;

the rendering processor further comprises circuitry for processing the dialogue channel audio signal and the center music channel audio signal such that the directional array radiates the dialogue channel and the center music channel with different radiation patterns;

wherein a difference between a maximum sound pressure level in any direction in a frequency range and a minimum sound pressure level in any direction in the frequency range is greater than-6 dB for a dialogue channel radiation pattern and between 0dB and-6 dB for a center music channel radiation pattern.

7. The audio system of claim 1, wherein the rendering processor renders the dialogue channel and the center music channel to different speakers.

8. The audio system of claim 1, wherein the rendering processor combines the center music channel with a left channel or a right channel or both.

9. An audio signal processing system comprising a discrete center channel input and signal processing circuitry for creating a center music channel;

wherein the signal processing circuitry comprises circuitry for processing channels other than the discrete center channel to create the center music channel;

wherein the dialogue channel and the center music channel are radiated by different elements of the same directional array.

10. The audio signal processing system of claim 9, wherein the signal processing circuitry comprises circuitry for processing the discrete center channel and other audio channels to create the center music channel.

11. The audio signal processing system of claim 9, further comprising circuitry for providing the discrete center channel to a first speaker and the center music channel to a second speaker.