Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
1998-12-03
2001-05-08
Dorvil, Richemond (Department: 2641)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704S228000
Reexamination Certificate
active
06230123
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to noise reduction and, in particular, to apparatuses for noise reduction, communication devices and systems comprising such apparatuses for noise reduction and to noise processing methods for reducing noise in audio signals.
DESCRIPTION OF THE PRIOR ART
A communication system for communication of speech comprises normally a microphone for picking up an acoustic signal which is supposed to include the speech to be communicated. In reality, however, not only speech but also noise which is present in the environment of the person speaking will be picked up by the microphone. Typical noisy environments are car environments, shopping malls and busy streets. It should be noted that people often use mobile communication devices, such as cellular phones, in this kind of noisy environments and, hence, the need for the implementation of an efficient noise reduction method is vital for this kind of devices.
One known form of a digital processing method for detecting and screening noise from speech in real time is presented in U.S. Pat. No. 5,012,519. The noise in an input signal is suppressed by splitting the input signal into spectral channels and decreasing the gain in each channel which has a low signal-to-noise ratio.
In U.S. Pat. No. 5,533,133 there is disclosed a method of noise suppression wherein noise is suppressed during pauses and silent periods in conversation, and voiced signals are freely passed. A voice activity detector is used to determine whether the signal comprises voice.
Whilst the known methods for noise reduction described above function quite adequately, they do have a number of disadvantages.
The implementation of the method for detecting and screening noise disclosed in U.S. Pat. No. 5,012,519 is complicated and expensive. A lot of (expensive) memory and a lot of power is needed to carry out the necessary Fast Fourier Transforms, FFTs, and the additional calculations. Memory is expensive especially in highly integrated equipment where the available chip surface is limited. Furthermore, power is always a scarce resource, especially in small battery-driven hand-held equipment such as mobile communication devices (e.g. cellular phones).
The implementation of the method of noise suppression disclosed in U.S. Pat. No. 5,533,133 is also complicated and expensive. Using a Digital Signal Processor, DSP, to implement the voice activity detector requires a lot of (expensive) memory and a lot of power to carry out all necessary calculations. Memory is expensive especially in highly integrated equipment where the available chip surface is limited. Furthermore, power is always a scarce resource, especially in small battery-driven hand-held equipment such as mobile communication devices (e.g. cellular phones).
It is an object of the present invention to provide apparatuses for noise reduction, communication devices and systems comprising such apparatuses for noise reduction and noise processing methods for reducing noise in audio signals which overcome or alleviate the above mentioned problems.
SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided an apparatus for noise reduction comprising an input terminal for receiving an input signal, first switching means connected to the input terminal, noise measuring means connected to the input terminal and being arranged to measure the noise level of the input signal, first comparator means connected to the noise measuring means for receiving a measured noise level, the first comparator means being arranged to compare the measured noise level with a first pre-determined noise level and to generate a first control signal accordingly, the first comparator means being connected to the first switching means and the first switching means being controlled by the first control signal, noise reduction means connected to the first switching means and being arranged to perform noise reduction of the input signal and to provide a noise reduced output signal, when it is activated, and is bypassed or turned off, when it is deactivated, and the first control signal is arranged to control the first switching means such that the first switching means deactivates the noise reduction means when the measured noise level is lower than the first pre-determined noise level.
According to a further aspect of the present invention there is provided a mobile communication device, such as a cellular phone, comprising a microphone, a radio receiver/transmitter and an air-interface wherein the signal from the microphone is connected to an apparatus for noise reduction according to the apparatus mentioned above, the output of the apparatus for noise reduction being transmitted by means of the receiver/transmitter and the air-interface.
According to a further aspect of the present invention there is provided an accessory equipment, e.g. a hands-free equipment, for a mobile communication device, such as a cellular phone, comprising a microphone wherein the signal from the microphone is connected to an apparatus for noise reduction according to the apparatus mentioned above.
According to a further aspect of the present invention there is provided a communication system comprising a microphone and an apparatus for noise reduction according to the apparatus mentioned above.
Preferably, the noise measuring means comprises a reduced voice activity detector which does not base its decision on the pitch but on the auto-correlation and the energy contents of the input signal. This has the advantage that a small buffer memory is needed and that a small amount of power is consumed when the necessary calculations are performed.
According to a further aspect of the present invention there is provided a noise processing method for reducing noise in audio signals comprising the steps of measuring the noise level of an input signal, determining if the measured noise level is lower than a first pre-determined noise level, and providing the input signal as output signal if the measured noise level is lower than the first pre-determined noise level and, otherwise, performing noise reduction on the input signal and providing the so processed input signal as output signal.
According to a further aspect of the present invention there is provided a noise processing method for reducing noise in audio signals comprising the steps of measuring the noise level of an input signal, determining if the measured noise level is lower than a first pre-determined noise level or higher than a second pre-determined noise level, and providing the input signal as output signal if the measured noise level is lower than the first pre-determined noise level, performing noise reduction on the input signal and providing the so processed input signal as output signal if the measured noise level is higher than or equal to the first pre-determined noise level but lower than the second pre-determined noise level and, otherwise, low pass filtering the input signal and providing the so filtered input signal as output signal.
The apparatus for noise reduction, the mobile communication device, the accessory equipment for a mobile communication device and the noise processing method according to the present invention solve the problems of the prior art. Comparing with U.S. Pat. No. 5,012,519 no FFT needs to be carried out for splitting the input signal into spectral channels. Therefore, a simple implementation is achieved which requires less memory capacity and, hence, is cheaper to implement, and which consumes less power. Furthermore, comparing with U.S. Pat. No. 5,533,133 a reduced voice activity detector may be chosen instead of a conventional voice activity detector. Therefore, a simple implementation is achieved which requires less memory capacity and, hence, is cheaper to implement, and which consumes less power.
Furthermore, the present invention has the advantage that noise reduction is only carried out when needed and, thereby, power is saved when no need for carrying out noise reduction exists. The need
Cavander Hans
Mekuria Fisseha
Dorvil Richemond
Jenkens & Gilchrist
Nolan Daniel A.
Telefonaktiebolaget LM Ericsson (publ)
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