1. Field of the Invention
The invention relates generally to audio enhancement systems, and more particularly, is directed to spatially enhancing audio for reproduction through a speaker.
2. Description of the Related Art
Many technology devices use a single small speaker to reproduce sound. Such devices include, but are not limited to, cellular telephones, personal digital assistants (PDA's), laptop computers, television sets, radios, and various small hand-held devices. Often such devices have poor audio capabilities and because only one speaker is utilized, they are monophonic. Thus, such systems often cannot accurately reproduce stereophonic information.
True stereophonic reproduction is characterized by at least two distinct qualities. The first quality is the directional separation of sound sources to produce the sensation of width. Directional separation is generally described as that which gives the listener the ability to judge the selective location of various sound sources, such as the position of instruments within an orchestra.
The second quality is the sensation of depth and presence that the directional separation creates. Presence is generally described as the feeling that the sounds seem to emerge, not from the reproducing loudspeakers themselves, but from positions in between and somewhat behind the loudspeakers. The term “ambience” is also used to describe this sensation of width, depth, and/or presence.
Attempts to reproduce stereophonic information with monophonic systems have included the approach of adding the stereophonic channels together with the intent of presenting information from all the channels through a single speaker. Unfortunately, merely adding the stereophonic information often results in the loss of information. For example, stereo information in one channel may be out of phase with information existing in another channel. When the two channels are added together, information is lost due to phase cancellation of the information.
Consequently the directional separation and the sensation of depth and presence are lost when different channels of stereophonic information are combined together using existing methods.
The system and method disclosed herein spatially enhances audio for reproduction through a single speaker. The audio enhancement system enhances the ambient component of the stereo input signals and mixes the enhanced ambient signal with the stereo input signals to produce monophonic audio information.
In one embodiment, the audio enhancement system generates a monophonic output from a pair of input signals. The system combines at least a portion of the first input with at least a portion of the second input to isolate difference information, enhances the difference information to produce enhanced difference information, and combines the enhanced difference information with the first and second inputs to generate an enhanced monophonic output.
In another embodiment, the audio enhancement system enhances the ambient component of the stereo input signals and mixes the enhanced ambient signal with the monophonic component of the input signals to produce monophonic audio information.
In an embodiment, the audio enhancement system generates a monophonic output from a pair of input signals. The system combines at least a portion of the first input with at least a portion of the second input to isolate difference information and combines a portion of the first input with the second input to isolate sum information. The system enhances the difference information to produce enhanced difference information, and combines the enhanced difference information with the sum information to generate an enhanced monophonic input.
In other embodiments, the system does not create the sum and difference information prior to combining the signals. The mixer isolates the sum and difference information, in addition to combining the enhanced information with the sum and difference information. A digital signal processor, for example, can implement an audio enhancement system of this type.
The stereo input signals are typically a left stereo channel input and a right stereo channel input. In addition, the stereo input signals can be synthetically generated from a monophonic input signal.
The enhancer used to enhance the ambient information comprises a filter, a gain, a filter and a gain, a delay, or the like. The characteristics of the enhancer may be dependent on the characteristics of the speaker, which reproduces the spatially enhanced monophonic audio.
In general, different speakers have different characteristics. More specifically, different sized speakers have different speaker coefficients. These differences accordingly require unique enhancer characteristics to enhance the stereo input information that is to be played through the speaker. Depending on the enhancer used, the audio enhancement system may need to adjust the phase relationship and other properties of the signals.
While the enhancer characteristics are dependent upon the speaker, the enhancer characteristics can also indicate if the audio enhancement system requires phase adjustment. The enhancer can be characterized by its magnitude and phase responses. If the magnitude response is approximately 0 dB at the frequency where the phase response is approximately 0°, audio information at that frequency will be lost when the enhanced signal mixes with the stereo input signals. To preserve the potentially canceled audio information, the audio enhancement system adjusts the phase relationship of the audio enhancement signals.
The system enhances the difference information to produce enhanced difference information, and phase adjusts the sum information to produce phase adjusted sum information. The system combines the enhanced difference information with the phase adjusted sum information to generate an enhanced monophonic output signal while audio information that potentially would be canceled is preserved.
The system can adjust the phase of the difference signal, or the system can adjust the phase of both the sum and difference signals. As mentioned previously, the sum and difference information need not be isolated prior to mixing the signals. The system can adjust the phase of one or both of the input signals and produce the sum and difference information in the mixer as intermediate steps.
In one embodiment, the phase adjuster adjusts the sum signal. In another embodiment, the phase adjuster adjusts the difference signal. In a further embodiment, the system phase adjusts both the sum information and the difference information. In yet a further embodiment, the system adjusts the phase response of the left and right channel input signals.
For purposes of summarizing the invention, certain aspects, advantages and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.
A general architecture that implements the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements.
An audio enhancement system combines stereophonic input signals to generate a monaural output signal with enhanced spatial characteristics. To avoid the loss of signal information that occurs when the stereo input signals are merely added, in one embodiment the audio enhancement system adjusts the phase of the signals. Phase adjustment is used to modify the frequency response of the system at frequencies where the system responses have approximately equal amplitudes and opposite phases. The adjustment at these frequencies avoids potential cancellation of information and preserves the original audio fidelity.
In one embodiment, the stereophonic information is processed to create an enhanced spatial impression when the information from different channels is combined to create a monophonic output. For example, an embodiment of the invention uses spatial enhancement to enhance the reproduction of stereo sound on a television having a monophonic audio output.
In an embodiment, for example, to enhance the reproduction of stereo sound on a television having a single speaker, the audio enhancement system determines the difference information that exists between different stereophonic channels. An enhancer then enhances the difference information to create an enhanced spatial impression. The enhancer can be a filter, such as a perspective filter, a band-pass filter, a high-pass filter, a low-pass filter, an all-pass filter, a gain, a filter and a gain, a delay, or the like. In an embodiment, the gain of the enhanced difference information is adjusted. In addition, a combiner combines the stereophonic channels to generate a sum signal. A mixer combines the enhanced difference information with the sum signal to generate an enhanced monophonic output. The result is a restoration of detail and the impression that the sound source is much larger when the sound is reproduced.
The sum and difference information need not be created prior to enhancing the signals, but can be created in the mixer. In another embodiment, an enhancer enhances the stereophonic channel inputs. The enhanced stereophonic information is mixed with the original stereophonic information to generate an enhanced monophonic output. In an embodiment, intermediate steps in the mixer generate the sum and difference information. A digital signal processor, for example, can implement the mixer.
In another implementation, the invention phase shifts the signals to preserve audio information that potentially could be lost when the signals combine to create the output. In an embodiment, for example, to enhance the reproduction of stereo sound on a cell phone speaker, the audio enhancement system extracts the difference information from the stereophonic input. An enhancer enhances the difference signal to create an enhanced spatial impression. The enhancer can be a filter, such as a perspective filter, a band-pass filter, a high-pass filter, a low-pass filter, an all-pass filter, or the like, a gain, a filter and a gain, a delay, or the like. In an embodiment, a gain control device adjusts the gain of the enhanced difference information. A combiner then generates the sum or monophonic information from the stereophonic signal and a phase adjuster adjusts the phase of the monophonic information. The phase adjuster can be a filter, such as a perspective filter, a lagging filter, a leading filter, a band-pass filter, a high-pass filter, a low-pass filter, an all-pass filter, or the like. The audio enhancement system combines the phase adjusted monophonic information and the enhanced difference information to produce the monophonic output.
In other embodiments, the phase adjuster adjusts the phase of the difference information. The audio enhancement system combines the monophonic information and the phase adjusted enhanced difference information to produce the monophonic output.
In further embodiments, the phase adjuster adjusts both the sum and the difference information, using, for example, a leading and a lagging filter, or the like. The audio enhancement system combines the phase adjusted monophonic information with the phase adjusted difference information to produce the monophonic output.
In yet other embodiments utilizing a phase adjustment, the sum and difference information need not be created prior to enhancing the signals, but can be created as intermediate steps in the mixer. A digital signal processor, for example, can implement the mixer. The audio enhancement system phase adjusts either stereophonic channel input or both stereophonic channel inputs. In addition, the enhancer enhances the stereophonic channel inputs.
In the embodiment where both input channels are phase adjusted, the audio enhancement system combines the phase adjusted stereophonic signals and the enhanced stereophonic information to produce the monophonic output.
In the embodiment where only one stereophonic input channel is phase adjusted, the audio enhancement system combines the phase adjusted stereophonic signal, the other original stereophonic signal, and the enhanced stereophonic channel information to produce the monophonic output.
In other embodiments, the stereo input signals are synthetically generated from a monaural input. The monophonic input information is processed to create an enhanced spatial impression. One approach delays information in the monaural input signal so that a spatial impression is created when the delayed information is combined with the original monaural signal to create the output.
In an embodiment to create a spatially enhanced monophonic output from a monophonic input signal, the audio enhancement system determines the difference information that exists between the monophonic input and the delayed monophonic input. An enhancer enhances the difference information to create a spatial impression. In addition, a combiner combines the monophonic input and the delayed monophonic input to generate a sum signal. In an embodiment, a gain control device adjusts the gain of the enhanced difference information. A mixer combines the enhanced difference information with the sum signal to generate an enhanced monophonic output. The result is the impression that the sound source is much larger when the sound is reproduced.
As summarized above, one embodiment of the invention comprises an audio enhancement system which generates a single audio output channel from two or more audio input channels, such that portions of the ambience present in the input channels are preserved in the output channel. For convenience and clarity of presentation, the discussion which follows assumes the input channels comprise stereophonic left and right channels and the audio enhancement system provides a single output.
The input, however, need not be limited to two stereo channels and embodiments of the invention can be used in many applications where the ambience of reproduced sound is produced by generating an output channel from a plurality of input channels. Furthermore, embodiments of the invention can be used in applications where the ambience of reproduced sound is produced by generating an output channel from at least one input channel. In addition, the input signals can comprise analog information or digital information, or the like. The output signal can also comprise analog information or digital information, or the like.
For a more detailed understanding of the invention, reference is first made to
The differencing device 118 produces a difference signal (L−R), which represents the spatial or ambient component of the stereo input signals, LIN and RIN. In an embodiment, the differencing device 118 comprises a subtractor. In another embodiment, the differencing device 118 comprises a combiner.
As further illustrated in
The enhancer 120 receives the spatial component (L−R) of the signal. The enhancer 120 enhances the spatial characteristics of the signal. In one embodiment, the enhancer 120 broadens and blends a perceived sound stage from the audio input information by selectively enhancing the sound information that provides a sense of spaciousness. The enhancer 120 produces an enhanced difference component (L−R)enhanced.
In an embodiment of the invention, the enhancer 120 comprises a perspective filter. In other embodiments of the invention, the enhancer 120 comprises a band-pass filter, an all-pass filter, a high-pass filter, a low-pass filter, or the like. In yet further embodiments of the invention, the enhancer 120 comprises a gain, a filter and a gain in series, a delay, or the like. An output of the enhancer 120 provides a first input to a mixer 124.
As illustrated in
The summing device 116 produces a sum signal, L+R, which represents the direct or monaural component of the stereo input signals, LIN and RIN. In an embodiment, the summing device 116 comprises an adder. In another embodiment, the summing device 116 comprises a combiner. An output of the summing device 116 provides an input to an enhancer 122.
The enhancer 122 phase adjusts the sum signal relative to the difference signal to preserve audio information. This audio information could potentially be canceled and lost when the mixer 124 combines the signals. The enhancer 122 produces a phase adjusted sum component (L+R)enhanced.
In an embodiment of the invention, the enhancer 122 comprises an all-pass filter. In other embodiments of the invention, the enhancer 122 comprises a band-pass filter, a high-pass filter, a low-pass filter, a leading filter, a lagging filter, or the like.
An output of the enhancer 122 provides a second input to the mixer 124 and, as described above, the output of the enhancer 120 provides the first input to the mixer 124. An output of the mixer 124 is an enhanced monophonic output 126.
The mixer 124 combines the enhanced difference component (L−R)enhanced with the phase adjusted direct component (L+R)enhanced to produce the monaural output 126 with enhanced spatial impression.
Depending on the enhancer 120 used in the audio enhancement system 100, as discussed previously, the system may need or may not need phase adjustment. In embodiments of the audio enhancement system 100 that do not need phase adjustment, the enhancer 122 is removed. The output of the summing device 116 provides the second input to the mixer 124. The mixer 124 combines the enhanced difference component (L−R)enhanced with the direct component (L+R) to produce the monaural output 126 with enhanced spatial impression.
In an embodiment of the invention, the enhancer 144 comprises a perspective filter. In other embodiments of the invention, the enhancer 144 comprises a band-pass filter, an all-pass filter, a high-pass filter, a low-pass filter, or the like. In yet further embodiments of the invention, the enhancer 144 comprises a gain, a filter and a gain in series, a delay, or the like.
An output of the enhancer, Lenhanced 144, provides a first input to a mixer 152.
Referring to
In an embodiment of the invention, the enhancer 146 comprises a perspective filter. In other embodiments of the invention, the enhancer 146 comprises a band-pass filter, an all-pass filter, a high-pass filter, a low-pass filter, or the like. In yet further embodiments of the invention, the enhancer 146 comprises a gain, a filter and a gain in series, a delay, or the like.
An output of the enhancer 146 provides an input to an inverter 148. The inverter 148 inverts the enhanced right channel signal Renhanced to produce an inverted right channel signal Rinverted. The output of the inverter 148 provides a second input to the mixer 152.
Again referring to
In an embodiment of the invention, the enhancer 142 comprises an all-pass filter. In other embodiments of the invention, the enhancer 142 comprises a band-pass filter, a high-pass filter, a low-pass filter, a leading filter, a lagging filter, or the like. An output of the enhancer 142, Ladjusted, provides a third input to the mixer 152.
Again referring to
In an embodiment of the invention, the enhancer 150 comprises an all-pass filter. In other embodiments of the invention, the enhancer 150 comprises a band-pass filter, a high-pass filter, a low-pass filter, a leading filter, a lagging filter, or the like. An output of the enhancer 150, Radjusted, provides a fourth input to the mixer 152.
The mixer 152 receives the phase adjusted and enhanced left and right channel signals. The mixer 152 combines the enhanced left and right signals, Lenhanced and Rinverted with the phase adjusted left and right signals, Ladjusted and Radjusted to produce the monaural output 126 with enhanced spatial impression.
Depending on the enhancers 144, 146 used in the audio enhancement system 140, as discussed previously, the system may need or may not need phase adjustment to prevent a loss of audio information. In embodiments of the audio enhancement system 140 that do not need phase adjustment, the enhancers 142, 150 are removed. The left input signal, LIN, 112 provides the third input to the mixer 152 and the right input, RIN, 114 provides the fourth input to the mixer 152. The mixer 152 combines the enhanced left and right signals, Lenhanced and Rinverted with the left and right input signals, LIN, 112 and RIN, 114 to produce the monaural output 126 with enhanced spatial impression.
Referring to
The output signals, Lpseudo, 186 and Rpseudo, 188 provide input signals to the audio enhancement systems 100, 140 in place of the input stereophonic signals, LIN, 112 and RIN, 114. Thus, the audio enhancement systems 100, 140 in combination with the monophonic input circuit 180 generate spatially enhanced monaural audio information from a monophonic input signal.
In an embodiment of the invention, the audio enhancement system 100, 140 can be combined with other systems for generating pseudo-stereophonic outputs from a monophonic input, such as, for example, the audio enhancement systems described in U.S. Pat. Nos. 4,841,572 and 6,590,983, the entirety of which are hereby incorporated herein by reference.
In another embodiment of the invention, the audio enhancement system 100, 140, 180 can be combined with other audio enhancement systems to provide additional audio enhancement effects, such as, for example, those audio enhancement systems described in U.S. Pat. Nos. 4,819,269, 4,836,329, 5,319,713, 5,333,201, 5,459,813, 5,638,452, 5,771,295, 5,784,468, 5,850,453, 5,912,976, the entirety of which are hereby incorporated herein by reference.
In an embodiment, discrete circuit components implement the audio enhancement system 100, 140, or 180. In an additional embodiment, the left 112 and right 114 stereo input signals are part of an audio-visual composite signal. In another embodiment, the audio enhancement system 100, 140, or 180 is constructed as a digital and analog hybrid circuit. In yet another embodiment, the audio enhancement system 100, 140, or 180 is contained within a multi-chip module.
In another embodiment of the invention, a digital signal processor (DSP) implements the audio enhancement system 100, 140, or 180 in digital format. In another embodiment, a computer implements the audio enhancement system 100, 140, or 180 in software.
The computers comprise, by way of example, processors, program logic, or other substrate configurations representing data and instructions, which operate as described herein. In other embodiments, the processors can comprise controller circuitry, processor circuitry, processors, general purpose single-chip or multi-chip microprocessors, digital signal processors, embedded microprocessors, microcontrollers and the like.
In an embodiment, the software may advantageously be implemented as one or more modules. The modules may advantageously be configured to execute on one or more processors. The modules may comprise, but are not limited to, any of the following: software or hardware components such as software object-oriented software components, class components and task components, processes methods, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, or variables.
The audio enhancement systems 100, 140, 180 of
In more detail, magnitude response range 202, 204 peaks between approximately 0 dB to approximately 20 dB at frequencies of between approximately 1 kHz to approximately 5 kHz. In further detail, the magnitude response 200 has an amplitude of approximately −18 dB at approximately 30 Hz and crosses 0 dB at approximately 260 Hz. The amplitude ramps up at approximately 19 dB per decade to a peak of approximately 9.5 dB at approximately 1.8 kHz. The amplitude rolls off at approximately 20 dB per decade to approximately −18 dB at approximately 20 kHz and crosses 0 dB at approximately 10 kHz.
In more detail, the phase response range 302, 304 has a phase angle of between approximately −180° to approximately 20° at frequencies of between approximately 20 Hz to approximately 300 Hz. The phase angle is between approximately −180° to approximately 150° at frequencies of between approximately 300 Hz to approximately 4 kHz and continues to rise to between approximately −100° to approximately 2000 at frequencies of between approximately 4 kHz to approximately 20 kHz. In further detail, the phase response 300 has a phase angle of approximately −90° at frequencies of between approximately 20 Hz to approximately 300 Hz. The phase response 300 rises to approximately 300 at approximately 3 kHz and continues to rise to approximately 800 at approximately 20 kHz at a rate of approximately 60° per decade.
In this example, the parameters of the enhancer 120 are chosen to enhance the audio for reproduction on a monophonic television set speaker. The circuit is designed such that the amplitude response of enhancer 120 is not 0 dB at the same frequency that the phase response is 0° or 180°. Otherwise, referring back to
The responses 400 and 600 of
Again referring to
In further detail, the phase difference 800 is approximately −200 at approximately 20 Hz and drops to approximately −180° at approximately 1.7 Hz at a rate of approximately 115° per decade. At approximately 1.7 kHz the phase difference between the left and right channels is approximately 180°. At the same frequency, however, the overall circuit 100 has a gain greater than 0 dB preserving information at the 1.7 kHz range that might otherwise be cancelled from out of phase mixing at the output stage. The phase difference 800 further drops to approximately −360° at approximately 20 kHz.
Referring to
In further detail, the magnitude response 900 has an amplitude of approximately −30 dB at approximately 250 Hz and ramps up at approximately 23 dB per decade to approximately −10 dB at approximately 2 kHz. The magnitude response 900 rises to a peak of approximately 2 dB at approximately 3.5 kHz, drops to a minimum of approximately −4.5 dB at approximately 4 kHz. The magnitude response 900 rises to a peak of approximately 0 dB at approximately 5 kHz and drops to a minimum of approximately −5 dB at approximately 6.4 kHz. The magnitude response rises to a peak of approximately 2 dB at a frequency of approximately 7.7 kHz and drops to approximately −27 dB at approximately 20 kHz at a rate of approximately 64 dB per decade.
In this example, the parameters of the filter 120 are chosen to enhance the audio for reproduction on a cell phone speaker. Referring to
The audio enhancement system utilized to generate the phase response difference 1100 is an embodiment of the audio enhancement system 100 with the filter 120 as described in
As shown in
The attenuation of the audio signal at approximately 3.6 kHz, 5.1 kHz, and 7 kHz is also shown in
In further detail, the magnitude response 1200 of
In addition, the cell phone embodiment of the audio enhancement system 100 is designed to keep the magnitude response of the inputs symmetrical, i.e., approximately equal, to prevent one input signal from overwhelming the other input signal. However, when the enhanced signals having opposite phase and nearly equal magnitude are added, certain information present in the signals may cancel.
To avoid losing audio information when the sum and difference signals are combined to generate the enhanced monaural output 126, embodiments of the audio enhancement systems 100, 140 comprise the enhancer 122, 142, and/or 150 to adjust the phase of the sum signal. As discussed previously, to prevent audio signal cancellation loss, other embodiments of the audio enhancement system 100, 140 can adjust the phase of the sum signal, the difference signal, the sum and difference signals, the enhanced difference signal, or the input signals. What is important is ensuring the proper relative phase of the signal paths which can be accomplished by modifying one or, as shown in
In further detail, the phase angle 1300 of
The magnitude-versus-frequency response of the all-pass filter 122 used in the cell phone embodiment of the audio enhancement system 100 is flat across the frequency spectrum, from 20 Hz to 20 kHz. An acceptable magnitude response range may vary from between −10 dB to 10 dB.
In another embodiment, the filter 122 modifies both phase and amplitude. In further embodiments of the invention, the filter 122 comprises a band-pass filter, a high-pass filter, a low-pass filter, a phase-leading filter, a phase-lagging filter, or other devices having phase adjusting characteristics.
Referring to
The mixer 124 combines the enhanced difference component (L−R)enhanced with the phase adjusted direct component (L+R)enhanced to produce the monaural output 126 with enhanced spatial impression.
As shown in
As shown in
Referring to
In addition, the system magnitude responses 1500 and 1600 have similarly shaped curves over the frequency spectrum. In this embodiment, the audio enhancement system 100 ideally has approximately equal gain in the left and right channel paths.
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.