Circuit, audio system and method for processing signals, and a harmonics generator

Abstract

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.

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.  
 
 
 
     
     
       2. The circuit as claimed in  claim 1 , wherein an input of the level detecting means communicates with an output of the selecting means. 
     
     
       3. The circuit as claimed in  claim 1 , wherein said circuit further comprises at least one further signal stage, including:
 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  claim 1 , in which the selecting means includes a low-pass filter or a band-pass filter. 
     
     
       5. The circuit as claimed in  claim 1 , wherein the added input audio signal includes signals with frequencies higher than the selected frequency band. 
     
     
       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.  
 
 
     
     
       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.  
 
 
 
     
     
       8. The circuit as claimed in  claim 7 , wherein an input of the detecting means communicates with an output of the selecting means. 
     
     
       9. The circuit as claimed in  claim 7 , wherein the circuit further comprises at least one further signal stage including:
 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.  
 
     
     
       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.  
 
 
 
     
     
       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.   
     
     
       12. The audio signal processing circuit as claimed in  claim 11 , wherein an input of the detecting means is coupled to an output of the selecting means. 
     
     
       13. The audio signal processing circuit as claimed in  claim 12 , wherein the audio signal processing circuit further comprises at least one further signal stage coupled between the input of the audio signal processing circuit and a further input of the adding means, the further signal stage comprising:
   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.     
     
     
       14. The audio signal processing circuit as claimed in  claim 11 , wherein the harmonics generating means comprises:
   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.     
     
     
       15. The audio signal processing circuit as claimed in  claim 11 , wherein the harmonics generating means comprises:
   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.     
     
     
       16. The audio signal processing circuit as claimed in  claim 15 , wherein 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.     
     
     
       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.