Enhanced conversion of wideband signals to narrowband signals
First Claim
1. A device, comprising:
- a control element for determining whether to convert a wideband speech signal into a narrowband speech signal;
a switch coupled to the control element, wherein the control element activates the switch if the control element determines that the wideband speech signal will be converted;
a filter for obtaining the wideband speech signal if the switch is activated, wherein the filter emphasizes a portion of the frequency spectrum of the wideband speech signal to output a signal with a non-flat frequency spectrum; and
a down sampler for decimating the output signal of the bandwidth switching filter.
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Accused Products
Abstract
Wideband speech signals must be converted to narrowband speech signals if the transmission medium or the destination terminal is constructed with narrowband constraints. A typical wideband-to-narrowband conversion method is the elimination of frequencies above 3400 Hz using a low pass filter and a down sampler. However, this method produces a muffled speech sound since the resulting narrowband signal has a flat frequency response. Methods and apparatus are presented herein to enhance the acoustic quality of a wideband-to-narrowband converted signal. A bandwidth switching filter is used to emphasize a mid-range frequency portion of the wideband signal so that the resulting narrowband signal has a non-flat frequency spectrum.
20 Citations
16 Claims
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1. A device, comprising:
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a control element for determining whether to convert a wideband speech signal into a narrowband speech signal; a switch coupled to the control element, wherein the control element activates the switch if the control element determines that the wideband speech signal will be converted; a filter for obtaining the wideband speech signal if the switch is activated, wherein the filter emphasizes a portion of the frequency spectrum of the wideband speech signal to output a signal with a non-flat frequency spectrum; and a down sampler for decimating the output signal of the bandwidth switching filter. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A device for converting a wideband speech signal into a narrowband speech signal, comprising:
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a control element for determining whether to convert the wideband speech signal into the narrowband speech signal; a switch coupled to the control element, wherein the control element activates the switch if the control element determines that the wideband speech signal will be converted; a down sampler coupled to the switch, wherein the down sampler is for decimating the wideband speech signal if the switch is activated; and a filter for obtaining the decimated wideband speech signal, wherein the filter emphasizes a portion of the frequency spectrum of the wideband speech signal to output a signal with a non-flat frequency spectrum. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A device comprising:
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a first element for creating a synthesized wideband speech signal; and a second element for enhancing the synthesized wideband speech signal, wherein the second element further comprises; a post-filter element; and a filter for emphasizing a middle range of the frequency spectrum of the synthesized wideband speech signal and attenuating a high range of the frequency spectrum of the synthesized wideband speech signal, wherein the middle range of the frequency spectrum is between 800 Hz and 3500 Hz; and wherein the high range of the frequency spectrum is above the middle range of the frequency spectrum.
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14. A method for transmitting wideband waveforms originating in a wireless communication system, comprising:
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obtaining a signal carrying a wideband waveform at a base station, wherein the wideband waveform is for further transmission from the base station to a target terminal; determining whether the target terminal can process the wideband waveform; if the target terminal cannot process the wideband waveform, then converting the wideband waveform into a narrowband waveform with a non-flat frequency response; and if the target terminal can process the wideband waveform, then transmitting the wideband waveform from the base station to the target terminal without converting the wideband waveform into a narrowband waveform. - View Dependent Claims (15, 16)
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Specification