EP0556992A1
Expired / Lapsed
EP
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Noise attenuation system
Assignee: Nokia Oyj
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Filing: 1993-02-08
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Granted: —
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Expires: 2013-02-08
Abstract
Abstract The invention relates to a noise attenuation system for voice signals. The invention is based on noise signal measurement during the tonal periods of the voice. The line spectrum structure of the spectrum of the tonal sounds is utilized in the noise measurement. In this way it is possible to measure the noise of different frequency bands with the aid of narrow-band filters.
Inventors
- 👤 Karl Juhani Jarvinen
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 08:48
CPC Classifications
H; H03; H03G; H03G9/00; H03G9/005; G; G10; G10L; G10L21/00; G10L21/02; G10L21/0208; H03G9/02; H03G9/025; H03H; H03H17/00; H03H17/02; H03H17/0248; H03H17/0264; H03H17/0272; G10L21/0216; G10L21/0232
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
171 words
A noise attenuation system for attenuating noise in a signal, comprising a filter for dividing the signal into a plurality of channels of a predetermined bandwidth, means for calculating the signal strength in each channel and means for estimating the noise strength in each channel; characterized by a buffer which enables the processing of the signal sequentially in distinct time periods of a predetermined length, coupled to a tonality decision block which classifies each period as tonal or toneless, a background noise measurement system which provides an estimate of the background noise strength depending on tonality to provide a signal to noise ratio for each channel in each time period, a gain calculation blocks for determining a gain coefficient for each channel in each time period, such that the channel attenuation may be increased for decreasing signal to noise ratio, coupled to a multiplication block for amplifying the channels dependent on the determined gain coefficient, and an assembly filter which reassembles the noise attenuated channels to produce a noise attenuated signal.
Claim 2
Dependent Claim
38 words
A noise attenuation system according to claim 1, characterized in that the background noise measurement system comprises a splitting filter group (301), a background noise estimation block (302) based on tonality, and a channel power estimation block (304).
Claim 3
Dependent Claim
37 words
A noise attenuation system according to claim 2, characterized in that the background noise estimation block (302) comprises a Quadrature Mirror Filter (308), a noise estimation filter (305), power calculation blocks (306), and minimum selection blocks (307).
Claim 4
Dependent Claim
25 words
A noise attenuation system according to claim 3, characterized in that the noise estimation filter (305) comprises a band-pass filter with a narrow pass-band (404).
Claim 5
Dependent Claim
71 words
A noise attenuation system according to claim 4, characterized in that the noise estimation filter is designed so as to have two narrow passbands (401), the mutual distance between the outer edges of the two narrow pass-bands of the commonly presented response of the channel splitting filter group and the noise estimation filter on each noise attenuation system channel is smaller than the lowest typical basic frequency of the voice signal.
Claim 6
Dependent Claim
23 words
A noise attenuation system according to claim 3,4 or 5, characterized in that the noise estimation filter (305) comprises a recursive elliptical filter.
Claim 7
Independent Claim
126 words
A method of attenuating noise in a signal comprising, dividing the signal into a plurality of channels of a predetermined bandwidth; processing the signal sequentially in distinct time periods of a predetermined length; making an estimate of the signal strength in each channel in each time period; classifying each period as tonal or toneless; making an estimate of the background noise strength depending on tonality to provide a signal to noise ratio for each channel in each time period; determining a gain coefficient for each channel in each time period, such that attenuation of the channel may be increase for decreasing signal to noise ratio; amplifying the channels dependent on the determined gain coefficient; and reassembling the noise attenuated channels to produce a noise attenuated signal.
Claim 8
Dependent Claim
25 words
A method according to claim 7, characterized in that a decision is periodically made on the tonality of the signal contained in each time period.
Claim 9
Dependent Claim
89 words
A method according to claim 8, characterized in that the noise signal strength is estimated based on tonality during periods classified as tonal, so that the powers of two narrow partial bands located at a mutual distance smaller than the basic frequency on each channel of the noise attenuation system are measured, and of these the lower partial band power is defined to represent the noise prevailing on the respective channel, whereby the background noise power of each channel can be selected by suitably scaling the partial band power.
Claim 10
Dependent Claim
28 words
A noise attenuation system according to any of claims 7 to 9, characterized in that noise estimation is also performed during periods which are not classified as tonal.
References Cited (Backward Citations)
US4628529A
Cited
EP0459362A1
Cited
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