Wideband signal transmission system
View Patent ↗Described is a transmission system ( 10 ) comprising a transmitter ( 12 ) for transmitting a narrowband audio signal to a receiver ( 14 ) via a transmission channel ( 16 ). The receiver ( 14 ) comprises a frequency domain bandwidth extender ( 18 ) for extending a bandwidth of the received narrowband audio signal by complementing the received narrowband audio signal with a highband extension thereof. The bandwidth extender ( 18 ) comprises an amplitude extender ( 24 ) for extending the bandwidth of an amplitude spectrum of the received narrowband audio signal by mapping narrowband amplitudes onto highband amplitudes. The bandwidth extender ( 18 ) further comprises a phase extender ( 26 ) for extending the bandwidth of a phase spectrum of the received narrowband signal and a combiner ( 28 ) for combining the extended amplitude spectrum and the extended phase spectrum into a bandwidth extended audio signal. The transmission system ( 10 ) is characterized in that the amplitude extender ( 24 ) comprises an amplitude mapper ( 42 ) and first and second frequency scale transformers ( 40,44 ). The first frequency scale transformer. ( 40 ) is arranged for transforming a linear frequency scale of the amplitude spectrum into a logarithmic frequency scale, e.g. the Bark scale. The amplitude mapper ( 42 ) is arranged for mapping according to the logarithmic frequency scale the narrowband amplitudes onto the highband amplitudes. The second frequency scale transformer ( 44 ) is arranged for transforming the logarithmic frequency scale of the extended amplitude spectrum into the linear frequency scale.
1. A transmission system comprising a transmitter for transmitting a narrowband audio signal to a receiver via a transmission channel, the receiver comprising a frequency domain bandwidth extender for extending a bandwidth of the received narrowband audio signal by complementing the received narrowband audio signal with a highband extension thereof, the bandwidth extender, comprising an amplitude extender for extending the bandwidth of an amplitude spectrum of the received narrowband audio signal by mapping narrowband amplitudes onto highband amplitudes, the bandwidth extender further comprising a phase extender for extending the bandwidth of a phase spectrum of the received narrowband signal and a combiner for combining the extended amplitude spectrum and the extended phase spectrum into a bandwidth extended audio signal, wherein the amplitude extender comprises an amplitude mapper and first and second frequency scale transformers, the first frequency scale transformer being arranged for transforming a linear frequency scale of the amplitude spectrum into a logarithmic frequency scale, the amplitude mapper being arranged for mapping according to the logarithmic frequency scale the narrowband amplitudes onto the highband amplitudes, the second frequency scale transformer being arranged for transforming the logarithmic frequency scale of the extended amplitude spectrum into the linear frequency scale.
2. The transmission system according to claim 1 , wherein the logarithmic frequency scale is the Bark scale.
3. The system of claim 2 , wherein the amplitude mapper further comprises a matrix selector for selecting a mapping matrix from a plurality of mapping matrices and a matrix multiplier for obtaining the highband amplitudes by multiplying the narrowband amplitudes with the selected mapping matrix.
4. The system of claim 3 , wherein amplitude mapper further comprises smoothing means for smoothing the highband amplitudes.
5. The system of claim 3 , wherein the amplitude mapper further comprises normalization means for normalizing the narrowband amplitudes and scaling means for scaling the highband amplitudes according to the volume of the received narrowband signal.
6. The system of claim 5 , wherein amplitude mapper further comprises smoothing means for smoothing the highband amplitudes.
7. The system of claim 2 , wherein the amplitude mapper further comprises normalization means for normalizing the narrowband amplitudes and scaling means for scaling the highband amplitudes according to the volume of the received narrowband signal.
8. The system of claim 7 , wherein amplitude mapper further comprises smoothing means for smoothing the highband amplitudes.
9. The transmission system according to claim 1 , wherein the amplitude mapper further comprises a matrix selector for selecting a mapping matrix from a plurality of mapping matrices and a matrix multiplier for obtaining the highband amplitudes by multiplying the narrowband amplitudes with the selected mapping matrix.
10. The system of claim 9 , wherein the amplitude mapper further comprises normalization means for normalizing the narrowband amplitudes and scaling means for scaling the highband amplitudes according to the volume of the received narrowband signal.
11. The system of claim 10 , wherein amplitude mapper further comprises smoothing means for smoothing the highband amplitudes.
12. The system of claim 9 , wherein amplitude mapper further comprises smoothing means for smoothing the highband amplitudes.
13. The transmission system according to claim 1 , wherein the amplitude mapper further comprises normalization means for normalizing the narrowband amplitudes and scaling means for scaling the highband amplitudes according to the volume of the received narrowband signal.
14. The transmission system according to claim 1 , wherein the amplitude mapper further comprises smoothing means ( 58 ) for smoothing the highband amplitudes.
15. A receiver for receiving, via a transmission channel, a narrowband audio signal from a transmitter, the receiver comprising a frequency domain bandwidth extender for extending a bandwidth of the received narrowband audio signal by complementing the received narrowband audio signal with a highband extension thereof, the bandwidth extender comprising an amplitude extender for extending the bandwidth of an amplitude spectrum of the received narrowband audio signal by mapping narrowband amplitudes onto highband amplitudes, the bandwidth extender further comprising a phase extender for extending the bandwidth of a phase spectrum of the received narrowband signal and a combiner for combining the extended amplitude spectrum and the extended phase spectrum into a bandwidth extended audio signal, wherein the amplitude extender comprises an amplitude mapper and first and second frequency scale transformers, the first frequency scale transformer being arranged for transforming a linear frequency scale of the amplitude spectrum into a logarithmic frequency scale, the amplitude mapper being arranged for mapping according to the logarithmic frequency scale the narrowband amplitudes onto the highband amplitudes, the second frequency scale transformer being arranged for transforming the logarithmic frequency scale of the extended amplitude spectrum into the linear frequency scale.
16. The receiver according to claim 15 , wherein the logarithmic frequency scale is the Bark scale.
17. The receiver according to claim 15 , characterized in that the amplitude mapper further comprises a matrix selector for selecting a mapping matrix from a plurality of mapping matrices and a matrix multiplier for obtaining the highband amplitudes by multiplying the narrowband amplitudes with the selected mapping matrix.
18. A method of receiving, via a transmission channel , a narrowband audio signal, the method comprising:
extending the bandwidth of an amplitude spectrum of the received narrowband audio signal by mapping narrowband amplitudes onto highband amplitudes,
extending the bandwidth of a phase spectrum of the received narrowband signal,
combining the extended amplitude spectrum and the extended phase spectrum into a bandwidth extended audio signal, characterized in that the method further comprises:
transforming a linear frequency scale of the amplitude spectrum into a logarithmic frequency scale,
mapping according to the logarithmic frequency scale the narrowband amplitudes onto the highband amplitudes,
transforming the logarithmic frequency scale of the extended amplitude spectrum into the linear frequency scale.
19. The method of claim 18 , wherein the logarithmic frequency scale is the Bark scale.
20. The method claim 18 , further comprising:
selecting a mapping matrix from a plurality of mapping matrices, and
obtaining the highband amplitudes by multiplying the narrowband amplitudes with the selected mapping matrix.