A circuit, audio system and method are presented for processing an audio signal, in which a frequency band is selected, harmonics are generated from the selected signal by a harmonics generator, wherein the harmonics are scaled by a level detected in at least a part of the spectrum of the audio signal related to the selected frequency band. Furthermore, a harmonic generator is presented for generating arbitrary harmonics of an input signal.
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6. An harmonics generator comprising:
a zero-crossing detector for detecting zero crossings in an input signal applied to the harmonics generator; and
a waveform generator for generating a waveform in response to the detected zero crossings, an amplitude of the generated waveform being controlled by a level of the input signal, whereby harmonics of the input signal are generated, wherein said waveform generator comprises:
a current source controlled by a level signal;
a capacitance; and
means for charging and discharging the capacitance in response to the detected zero crossings.
0. 11. A circuit for processing an audio signal, said audio signal processing circuit comprising:
an input for receiving an audio signal and an output for supplying an output signal;
selecting means coupled to the input, said selecting means selecting a frequency band of the audio signal;
harmonics generating means coupled to the selecting means for generating harmonics of signals in the selected frequency band of the audio signal;
adding means coupled to the input of said audio signal processing circuit and to an output of the harmonics generating means for supplying a sum of the audio signal and the generated harmonics to the output of the circuit;
detecting means for detecting a level of at least a part of the spectrum of the audio signal including the selected frequency band; and
scaling means for scaling the generated harmonics in response to said detected level;
wherein the selecting means has a low-pass transfer function, and the input of the audio signal processing circuit is coupled to the adding means via a filter having a high-pass transfer function for selecting frequencies higher than those which are selected by the selecting means.
1. A circuit comprising:
selecting means for selecting a frequency band of an audio input signal;
harmonics generator means for generating harmonics of signals in the selected frequency band of the audio input signal to provide generated harmonics;
adding means for supplying a sum of the audio input signal and scaled harmonics;
level detecting means for detecting a level of at least a part of the spectrum of the audio input signal including the selected frequency band; and
scaling means for scaling the generated harmonics in response to the detected level to provide the scaled harmonics, and
wherein the harmonics generator comprises:
a zero-crossing detector for detecting zero crossings in signals including signals of the selected frequency band; and
a waveform generator for generating a waveform in response to detected zero crossings, an amplitude of the generated waveform being controlled by the level supplied by the level detecting means, and wherein the waveform generator comprises:
a current source controlled by the detected level supplied by the level detecting means;
a capacitance; and
means for charging and discharging the capacitance in response to the detected zero crossings.
10. A circuit comprising:
selecting means for selecting a frequency band of an audio input signal, the selected frequency band being lower than the highest signal frequencies of the audio input signal;
harmonics generator means for generating harmonics of signals in the selected frequency band of the audio input signal to provide generated harmonics;
adding means for supplying a sum of the audio input signal and scaled harmonics;
level detecting means for detecting a level of at least a part of the spectrum of the audio input signal including the selected frequency band; and
scaling means for scaling the generated harmonics in response to the detected level to provide the scaled harmonics, wherein the harmonics generator comprises:
a zero-crossing detector for detecting zero crossings in signals including signals of the selected frequency band; and
a waveform generator for generating a waveform in response to detected zero crossings, an amplitude of the generated waveform being controlled by the level supplied by the level detecting means, and wherein the waveform generator comprises:
a current source controlled by the detected level supplied by the level detecting means;
a capacitance; and
means for charging and discharging the capacitance in response to the detected zero crossings.
0. 17. An audio system comprising:
a signal source for providing an audio signal;
a circuit for improving low-frequency perception coupled to said signal source for receiving said audio signal; and
a loudspeaker coupled to an output of said circuit for improving low-frequency perception,
wherein said circuit for improving low-frequency perception comprises:
an input for receiving the audio signal and an output for supplying an output signal;
selecting means coupled to the input for selecting a frequency band of the audio signal;
harmonics generating means coupled to the selecting means for generating harmonics of signals in the selected frequency band of the audio signal;
adding means coupled to the input and to an output of the harmonics generating means for supplying a sum of the input signal and the generated harmonics to the output of the circuit for improving low-frequency perception;
detecting means for detecting a level of at least a part of the spectrum of the audio signal including the selected frequency band; and
scaling means for scaling the generated harmonics in response to said detected level;
wherein the selecting means has a low-pass transfer function, and the input of the circuit for improving low-frequency perception is coupled to the adding means via a filter having a high-pass transfer function for selecting frequencies higher than those which are selected by the selecting means.
7. A circuit comprising:
selecting means for selecting a frequency band of an audio input signal and having a low-pass transfer function;
harmonics generator means for generating harmonics of signals in the selected frequency band of the audio signal to provide generated harmonics;
adding means for supplying a sum of a filtered audio signal and scaled harmonics;
level detecting means for detecting a level of at least a part of the spectrum of the audio signal including the selected frequency band;
scaling means for scaling the generated harmonics in response to the detected level to provide the scaled harmonics; and
a filter for filtering the audio input signal and having a high-pass transfer function for selecting frequencies higher than those which are selected by the selecting means to provide the filtered audio signal, wherein the harmonics generator comprises:
a zero-crossing detector for detecting zero crossings in signals including signals in the selected frequency band; and
a waveform generator for generating a waveform in response to detected zero crossings, an amplitude of the generated waveform being controlled by the detected level supplied by the level detecting means, and wherein the waveform generator comprises:
a current source controlled by the detected level supplied by the level detecting means;
a capacitance; and
means for charging and discharging the capacitance depending on the detected zero crossings.
2. The circuit as claimed in
3. The circuit as claimed in
further selecting means for selecting a part of the input signal adjacent, in frequency, to the selected frequency band of the selecting means;
a further harmonics generator for generating harmonics of signals in the part of the audio input signal selected by the further selecting means;
further detecting means for detecting a level of the signals in the part of the audio input signal selected by the further selecting means; and
further scaling means for scaling the harmonics generated by the further harmonics generator in response to the level detected by the further detecting means, and wherein the adding means further adds the scaled harmonics from the further scaling means for supplying the sum.
4. The circuit as claimed in
5. The circuit as claimed in
8. The circuit as claimed in
9. The circuit as claimed in
further selecting means for selecting a part of the input signal adjacent, in frequency, to the selected frequency band of the selecting means;
a further harmonics generator communicating with the further selecting means for generating harmonics of signals in the part of the audio input signal selected by the further selecting means;
further level detecting means for detecting a level of the signals in at least the part of the audio input signal selected by the further selecting means; and
further scaling means for scaling the harmonics generated by the further harmonics generator in response to the level detected by the further level detecting means, and wherein the adding means also adds the scaled harmonics from the further scaling means for supplying the sum.
0. 12. The audio signal processing circuit as claimed in
0. 13. The audio signal processing circuit as claimed in
a further selecting means coupled to the input, said further selecting means having a selection characteristic for selecting a part of the input signal adjacent, in frequency, to the selected frequency band of the selecting means;
a further harmonics generating means coupled to the further selecting means for generating harmonics of signals in the part of the input signal selected by the further selecting means;
further detecting means coupled to the further selecting means for detecting a level of the signals in the part of the input signal selected by the further selecting means; and
further scaling means for scaling the harmonics generated by the further harmonics generating means in response to said level detected by said further detecting means.
0. 14. The audio signal processing circuit as claimed in
coefficient scaling means;
further coefficient scaling means;
further adding means; and
a plurality of cascaded multipliers each having two inputs, the inputs of a first multiplier of the plurality of cascaded multipliers being coupled to the input of the harmonics generating means, an input of each of the remaining multipliers being coupled to the input of the harmonics generating means, and the remaining input of each of the remaining multipliers being coupled to an output of a preceding multiplier, and the outputs of the plurality of cascaded multipliers being coupled, via the coefficient scaling means, to respective inputs of the further adding means, the input of the harmonics generating means being coupled, via the further coefficient, scaling means, to a further input of the further adding means, the further adding means further receiving a constant value, and an output of the further adding means supplying the generated harmonics.
0. 15. The audio signal processing circuit as claimed in
a zero-crossing detector; and
a waveform generator for generating a waveform in response to detected zero crossings, an amplitude of the generated waveform being controlled by the level supplied by the detecting means.
0. 16. The audio signal processing circuit as claimed in
a current source controlled by the level supplied by the detecting means;
a capacitance; and
means for charging and discharging the capacitance in response to the detected zero crossings.
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1. Field of the Invention
The invention relates to a circuit for processing an audio signal, comprising:
The invention also relates to an audio reproduction system comprising such a circuit.
The invention further relates to a method for processing an audio signal, comprising the steps of:
2. Description of the Related Art
A circuit according to the preamble is known from European Patent Application EP-A 546 619. In the known circuit, a low frequency band of an input signal is selected and supplied to a harmonics generator for generating harmonics of the selected signal. In this way, low-frequency perception of the audio signal is improved upon. In the known circuit a full-wave rectifier is used as harmonics generator. A drawback of the full-wave rectifier is that it generates only even harmonics.
An object of the invention is to provide a circuit for processing an audio signal, wherein any non-linear device may be used as a harmonics generator for generating any selection of harmonics desired.
A circuit according to the invention is characterized in that the circuit further comprises:
An embodiment of the circuit, according to the invention, is characterized in that the input is coupled to the adding means via a filter having a high-pass transfer function for selecting frequencies higher than those which are selected by the selecting means. By this measure, no overlap in spectrum of the signals supplied to the adding means takes place, thus avoiding an extra and unnatural boosting of those frequencies, which would otherwise be present due to the overlap of frequency ranges.
An embodiment of the circuit, according to the invention, is characterized in that an input of the detecting means is coupled to an output of the selecting means. Through this measure, the amplitude of the generated harmonics is directly related to the amplitude of the input signal of the harmonics generator. In addition to that, in this way the selecting means serves a double purpose, both for the detecting of the level, and for selecting the signal for the harmonics generator. This results in a more economic circuit.
An embodiment of the circuit, according to the invention, is characterized in that the circuit comprises at least one further signal stage, coupled between the input and a further input of the adding means, the signal stage comprising:
By providing two (or more) parallel paths for generating harmonics, the effect of intermodulation is reduced. This intermodulation results if two or more strong low frequencies are present at the input of the harmonics generator. By selecting the pass-bands of the selecting means sufficiently narrow and providing a plurality of harmonics generators, each supplied by respective selecting means having adjacent pass-bands, the chances of two strong low frequencies present at the input of one of the harmonics generator is substantially reduced. By providing each individual signal path with its individual detecting means, the harmonics generated in each path will have an amplitude related to only the signal component from which the harmonics are generated. This results in a more natural sound.
An embodiment of the circuit, according to the invention, is characterized in that the harmonics generator comprises a plurality of cascaded multipliers, each having two inputs and an output, the inputs of the first of the cascade of multipliers being coupled to an input of the harmonics generator, a remaining input of each of the remaining multipliers being coupled to the input of the harmonics generator, an output of each of the multipliers being coupled via a coefficient to a respective input of further adding means, the input of the harmonics generator being coupled via a coefficient to an input of the adding means, the adding means further receiving a constant value, an output of the adding means supplying the generated harmonics.
Through this measure, a versatile harmonics generator is created. By varying the number of multipliers and the values of the coefficients, an arbitrary number of harmonics can be generated with freely determinable amplitudes.
An embodiment of the circuit, according to the invention, is characterized in that the harmonics generator comprises a zero-crossing detector and a waveform generator for generating a waveform in response to the detected zero crossings, an amplitude of the generated waveform being controlled by the level supplied by the detecting means.
By dividing the harmonics generator into a zero-crossing detector and waveform generating means, it is possible to generate harmonics on the basis of the detected zero crossings, with fixed amplitudes. By choosing the appropriate waveform, it is possible to adjust the number and amplitudes of the harmonics. By controlling the amplitudes with the detected level, the generated harmonics are adapted to the audio signal.
An embodiment of the circuit, according to the invention, is characterized in that the waveform generator comprises a current source controlled by the level supplied by the detecting means, a capacitance and means for charging and discharging the capacitance in response to the detected zero crossings. This is a simple and advantageous embodiment of a waveform generator for use in the invention.
An embodiment of an audio system comprising at least one speaker, according to the invention, is characterized in that the selected frequency band of the selecting means is non-overlapping with the high-pass characteristic of the speaker. By this measure, the circuit is adapted to compensate the low-frequency deficiencies of the speaker, as only those frequencies are treated by the circuit which the speaker can not reproduce adequately.
A method, according to the invention, is characterized in that the method further comprises the step of scaling the generated harmonics in response to a level of at least a part of the spectrum of the audio signal including the selected frequency band.
The invention further provides a harmonics generator for generating harmonics of an input signal, comprising a plurality of cascaded multipliers, each having two inputs and an output, the inputs of the first of the cascade of multipliers being coupled to an input of the harmonics generator, a remaining input of each of the remaining multipliers being coupled to the input of the harmonics generator, an output of each of the multipliers being coupled via a coefficient to a respective input of further adding means, the input of the harmonics generator being coupled via a coefficient to an input of the adding means, the adding means further receiving a constant value, an output of the adding means supplying the generated harmonics. By selecting an appropriate number of multipliers and selecting appropriate values for the coefficients, it is possible to generate an arbitrary number of harmonics with individually selectable amplitudes.
The invention also provides a harmonics generator for generating harmonics of an input signal, comprising a zero-crossing detector for detecting zero crossings in the input signal applied to the harmonics generator, and a waveform generator for generating a waveform in response to the detected zero crossings, an amplitude of the generated waveform being controlled by a level of the input signal.
This is a simple implementation of a harmonics generator. By generating a waveform in response to the detected zero crossings, harmonics are generated, which will have a constant amplitude. Now the scaling of the generated harmonics can be done by controlling the amplitude of the harmonics by the level of the input signal. In this way, the amplitudes of the harmonics can be made proportional to the level of the input signal. By choosing the appropriate waveform (square/sawtooth/triangle, etc.), the desired harmonics can be generated.
An embodiment of the harmonics generator is characterized in that the waveform generator comprises a current source controlled by the level supplied by the detecting means, a capacitance, and means for charging and discharging the capacitance in response to the detected zero crossings. This provides a simple way of generating the desired waveform in response to the detected zero crossings. These harmonics generators may also be used in the known circuit or even separately from this circuit or the circuits described previously.
The above object and features of the present invention will be more apparent from the following description of the preferred embodiments with reference to the drawings, wherein:
In the figures, identical parts are provided with the same reference numbers.
The invention is by no means limited to the examples given above. For example, a band-pass filter 24 may be incorporated also in the circuits of
Aarts, Ronaldus M., Straetemans, Stephanus P.
Patent | Priority | Assignee | Title |
10267860, | Mar 11 2014 | Rolls-Royce plc | Fault detection in induction machines |
7787640, | Apr 24 2003 | Massachusetts Institute of Technology | System and method for spectral enhancement employing compression and expansion |
7991171, | Apr 13 2007 | WHEATSTONE CORPORATION | Method and apparatus for processing an audio signal in multiple frequency bands |
8150067, | Mar 16 2007 | Sony Corporation | Bass enhancing method, signal processing device, and audio reproducing system |
8934643, | Apr 09 2008 | Koninklijke Philips Electronics N V | Generation of a drive signal for sound transducer |
8958573, | Dec 01 2010 | Malikie Innovations Limited | Apparatus, systems and methods for controlling an electronic device using an accessory |
Patent | Priority | Assignee | Title |
4463650, | Nov 19 1981 | System for converting oral music to instrumental music | |
4532848, | Jan 09 1984 | Kawai Musical Instrument Mfg. Co., Ltd. | Generation of mutation pitches in an electronic musical instrument |
5388159, | Dec 20 1991 | Clarion Co., Ltd. | Equalizing circuit for reproduced signals |
5438625, | Apr 09 1991 | KLIPPEL, WOLFGANG | Arrangement to correct the linear and nonlinear transfer behavior or electro-acoustical transducers |
6111960, | Aug 05 1996 | U.S. Philips Corporation | Circuit, audio system and method for processing signals, and a harmonics generator |
EP546619, |
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