Enhanced Conversion of Wideband Signals to Narrowband Signals
First Claim
1. An apparatus for converting a wideband speech signal into a narrowband speech signal, comprising:
- 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 bandwidth switching filter for receiving the wideband speech signal if the switch is activated, wherein the bandwidth switching filter emphasizes a portion of the frequency spectrum of the wideband speech signal to produce an output signal with a non-flat frequency spectrum; and
a down sampler for decimating the output signal of the bandwidth switching filter.
1 Assignment
0 Petitions
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.
-
Citations
22 Claims
-
1. An apparatus for converting a wideband speech signal into a narrowband speech signal, comprising:
-
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 bandwidth switching filter for receiving the wideband speech signal if the switch is activated, wherein the bandwidth switching filter emphasizes a portion of the frequency spectrum of the wideband speech signal to produce an output 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)
-
-
7. An apparatus for converting a wideband speech signal into a narrowband speech signal, comprising:
-
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 bandwidth switching filter for receiving the decimated wideband speech signal, wherein the bandwidth switching filter emphasizes a portion of the frequency spectrum of the wideband speech signal to produce an output signal with a non-flat frequency spectrum. - View Dependent Claims (8, 9, 10, 11, 12)
-
-
13. An apparatus for decoding a wideband speech signal and for converting the wideband speech signal into a narrowband speech signal, comprising:
-
a speech synthesis element for creating a synthesized wideband speech signal; and
a post-processing element for enhancing the synthesized wideband speech signal, wherein the post-processing element further comprises;
a post-filter element; and
a bandwidth switching 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. - View Dependent Claims (14, 15)
-
-
16. A method for transmitting wideband waveforms originating in a wireless communication system, comprising:
-
receiving 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 destination;
determining whether the target destination can process the wideband waveform;
if the target destination cannot process the wideband waveform, then converting the wideband waveform into a narrowband waveform with a non-flat frequency response; and
if the target destination can process the wideband waveform, then transmitting the wideband waveform from the base station to the target destination without converting the wideband waveform into a narrowband waveform. - View Dependent Claims (17, 18)
-
-
19. A method for determining whether to convert a wideband signal into a narrowband signal, comprising:
-
receiving a final destination address originating from a remote unit, comparing the final destination address to a plurality of destination addresses within an identification database;
if the final destination address matches one of the plurality of destination addresses within the identification database, then transmitting the wideband signal to the final destination address; and
if the final destination address does not match one of the plurality of destination addresses within the identification database, then;
converting the wideband signal into the narrowband signal, wherein the narrowband signal has a non-flat frequency response; and
transmitting the narrowband signal to the final destination address.
-
-
20. An apparatus for determining whether to convert a wideband signal into a narrowband signal, comprising:
-
a memory;
a processor for implementing an instruction set stored within the memory, the instruction set for performing the steps of;
receiving a final destination address originating from a remote unit, comparing the final destination address to a plurality of destination addresses within an identification database;
if the final destination address matches one of the plurality of destination addresses within the identification database, then transmitting the wideband signal to the final destination address; and
if the final destination address does not match one of the plurality of destination addresses within the identification database, then;
converting the wideband signal into the narrowband signal, wherein the narrowband signal has a non-flat frequency response; and
transmitting the narrowband signal to the final destination address.
-
-
21. An apparatus for converting a wideband signal into a narrowband signal, comprising:
-
a filter for emphasizing a mid-range portion of the frequency response of the wideband signal and for attenuating a high range portion of the frequency response of the wideband signal, wherein the output of the filter is a narrowband signal with a non-flat frequency response; and
a down sampler for decimating the sampling rate of the wideband signal.
-
-
22. An apparatus for converting a wideband signal into a narrowband signal, comprising:
-
means for receiving a final destination address and the wideband signal originating from a remote unit, means for comparing the final destination address to a plurality of destination addresses within an identification database;
means for determining whether to transmit the wideband signal to the final destination address or to convert the wideband signal into the narrowband signal, wherein the narrowband signal has a non-flat frequency response; and
means for transmitting the narrowband signal to the final destination address.
-
Specification