Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R3/00—Circuits for transducers, loudspeakers or microphones
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S1/00—Two-channel systems

Definitions

• Figures 6 and 7 show second and third embodiments, respectively, of an integrator for use in the present invention
• Figures 8 and 9 show first and second embodiments, respectively, of a limiter which can be used in the present invention in combination with an integrator as shown, for example, in Figures 4 and 5,
• FIG. 1 shows a block diagram of an audio system according to the invention.
• the audio system comprises a signal source 10, which is coupled via a circuit 12 and an amplifier 14, respectively, to a loudspeaker 16.
• the signal source 10 may derive its signal from a CD, a cassette or a received signal or any other audio source.
• the circuit 12 processes the audio signal supplied by the signal source 10 in such a way that low-frequency tones, which are present in the audio signal but cannot be reproduced by the loudspeaker 16 because of its limited size, are replaced by harmonics of these tones. These harmonics, which can be reproduced by the loudspeaker 16, evoke the illusion of a higher bass response. This psychoacoustical phenomenon is often referred to as virtual pitch or missing fundamental.
• the audio signal, which is processed by the circuit 12 is thereafter amplified by the amplifier 14. This amplified signal is then reproduced by the loudspeaker 16.
• FIG. 2 shows a block diagram of a circuit 12 for processing an audio signal according to the invention.
• the circuit 12 comprises an input 20 for receiving an audio signal and an output 26 for supplying an output signal.
• the circuit 12 further comprises a harmonics generator 22 coupled to the input 20 and adding means 24, coupled to the input 20 and the harmonics generator 22, for supplying the sum of the audio signal and the output signal of the harmonics generator 22 to the output 26.
• a first filter may be inserted between the input 20 and the harmonics generator 22.
• this first filter is embodied so as to pass those low-frequency components in the audio signal which cannot be reproduced by the loudspeaker 16, while at the same time spurious dc components in the audio signal are blocked.
• a second filter in the circuit 12 between the harmonics generator 22 and the adding means 24. By means of this second filter the number of harmonics which are reproduced by the loudspeaker 16 can be controlled.
• a third filter can be inserted in the circuit 12 between the input 20 and the adding means 24. Preferably, this third filter is used to block those low-frequency components in the audio signal which cannot be reproduced by the 5 loudspeaker, thus preventing an overload of the loudspeaker 16.
• FIG. 3 shows a block diagram of a harmonics generator 22 according to the invention.
• the harmonics generator 22 comprises an input 30 for receiving an audio signal and an output 38 for supplying an output signal.
• the harmonics generator 22 further comprises an integrator 34 and. coupled thereto, a resetting means 36.
• the integrator 34 integrates the 0 audio signal received by the input 30 and supplies the integrated signal to the output 38.
• the resetting means 36 are embodied so as to reset the integrator 34 at resetting times.
• the output signal comprises both odd and even harmonics, whereby the amplitudes of these harmonics are substantially equal to each other.
• the amplitude of the generated harmonics is proportional to the amplitude of the audio signal, no annoying distortions 5 are introduced by the harmonics generator 22.
• the resetting times can be determined by the resetting means 36 in a number of different ways.
• the resetting means 36 can determine the resetting times in dependence on some properties of the audio signal, for instance the period, the amplitude or the zero crossings. It is also possible that the resetting means 36 determine the resetting times in dependence on 0 similar properties of the output signal. Furthermore, the resetting means 36 may determine the resetting times in dependence on both the audio signal and the output signal. It may be clear that in a specific embodiment of the harmonics generator 22 according to the invention, only one or both of the connections 35 and 37 are present.
• the harmonics generator 22 may further comprise a rectifier 32, which 5 rectifies the audio signal received by the input 30.
• FIG. 4 shows a first embodiment of an integrator 34 which can be used in the present invention.
• the integrator 34 comprises an input 40 for receiving an input signal and an output 52 for supplying an output signal.
• the integrator 34 further comprises an operational amplifier 50, the positive input of which is grounded.
• the switch 44 is controlled by the reset signal RST, which is generated by the resetting means 36 in such a way that the switch 44 is closed at resetting times.
• the input signal received at the input 40 is integrated by this embodiment of the integrator 34, whereby the integrated signal is supplied to the output 52.
• the integrator is reset, i.e. the capacitor 46 is discharged and the output signal is reset to zero, when the switch 44 is closed.
• Figure 5 shows a circuit for use in the present invention, in which an integrator 34 and a resetting means 36 are combined.
• This circuit comprises an input 64 for receiving an input signal and an output 66 for supplying an output signal.
• the circuit further comprises the elements of Figure 4 which are needed for the integration of the input signal, i.e. the resistors 42 and 48, the operational amplifier 50 and the capacitor 46.
• the switch 44 is implemented by means of the transistor 62. Because the base of this transistor 62 is coupled via an inverter 60 to the input 64, the transistor 62 conducts (i.e. the switch 44 is closed and the integrator is reset) when the input signal is negative. On the other hand, when the input signal is positive, the transistor 62 does not conduct, i.e. the switch 44 is open.
• Some low-frequency tones, which are reproduced by the audio system according to the invention, are perceived by human beings as having a higher loudness than the loudness of the corresponding low-frequency tones which are present in the audio signal.
• the integrator 34 can be embodied so as to limit the amplitude of the integrated signal. In this way, the perceived loudness of low- frequency tones can be controlled, preferably in such a manner that the perceived loudness is substantially equal to the original loudness.
• Figures 8 and 9 show first and second embodiments, respectively, of a limiter which can be used to limit the range of the output signal of an integrator 34 as shown, for example, in Figures 4 and 5.
• the limiter comprises an inverting amplifier, which is comprised of an input 90, an output 102, an operational amplifier 100 and two resistors 92 and 98.
• the absolute value of the voltage gain of this inverting amplifier is equal to the resistance of the resistor 98 divided by the resistance of the resistor 92.
• two diodes 94 and 96 which are placed in parallel with the resistor 98, prevent an output signal of the inverting amplifier from exceeding certain voltage limits.
• the amplitude of the integrated signal can be limited gradually, thus enabling a smooth control of the perceived loudness of low- frequency tones.
• This adaptation of the integration time-constant can be achieved by altering the resistance of the resistor 42 and/or the capacitance of the capacitor 46.
• the effective resistance of the resistor 42 can, be changed, for instance by switching one or more resistors in series or parallel with the resistor 42.
• the effective capacitance of the capacitor 46 can be changed, for instance, by switching one or more capacitors in series or in parallel with the capacitor 46.
• the wave forms b and c can be generated by the harmonics generator 22 in a similar fashion, whereby, for wave form b, the integrator 34 is reset at the end of each second period of the input signal, and for wave form c, the integrator 34 is reset at each zero crossing of the input signal.
• the wave form d can be generated by the harmonics generator 22, whereby the harmonics generator 22 comprises the combination of the integrator 34 and the resetting means 36 as depicted in Figure 5. In this case, the harmonics generator 22 does not comprise the rectifier 22.
• Wave forms e, f, and g in Figure 10 can be generated by the harmonics generator 22 according to the invention in a similar fashion as described above for wave form a.
• Wave form e is generated by the harmonics generator 22, which is embodied so as to stop the integration in dependence on the amplitude of the integrated signal.
• the harmonics generator 22 may comprise an integrator 34 as shown in Figures 6 and 7, or an integrator 34 as depicted in Figure 4 in combination with a limiter circuit as shown, for example, in Figures 8 and 9.
• the wave forms f and g illustrate the adaptation of an integration time- constant by the integrator 34.
• the integration time-constant of the integrator 34 is adapted once during each period of the input signal, whereby this adaptation depends on, for example, the amplitude or the frequency of the integrated signal.
• Waveform g may be generated in a similar fashion, whereby the integrator 34 is adapted twice during each period of the input signal.
• the integrator 34 it is also possible to arrange the integrator 34 in such a way that more than two adaptations of the integration time-constant are supported.
• the signal processing performed in the entities according to the invention may also be performed by a dedicated integrated circuit or in software running on a programmable processor.
• the resistor 48 may be omitted.
• a desired limitation of the amplitude of the output signal of the harmonics generator 22 can also be achieved by means of a multiplication of the input or output signal with a certain multiplication factor.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
• Circuit For Audible Band Transducer (AREA)
• Amplifiers (AREA)
• Noise Elimination (AREA)

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• 1998
  • 1998-10-19 KR KR1019997006130A patent/KR100560319B1/ko not_active IP Right Cessation
  • 1998-10-19 EP EP98946659A patent/EP0958710B1/de not_active Expired - Lifetime
  • 1998-10-19 DE DE69825422T patent/DE69825422T2/de not_active Expired - Fee Related
  • 1998-10-19 CN CNB988031671A patent/CN1153504C/zh not_active Expired - Fee Related
  • 1998-10-19 JP JP52579299A patent/JP2001507912A/ja not_active Ceased
  • 1998-10-19 WO PCT/IB1998/001648 patent/WO1999025151A1/en active IP Right Grant
  • 1998-10-29 TW TW087117968A patent/TW393872B/zh not_active IP Right Cessation
  • 1998-11-05 MY MYPI98005044A patent/MY122113A/en unknown

Non-Patent Citations (1)

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