Equalization of speech signal in mobile phone

• US 6,011,853 A
• Filed: 08/30/1996
• Issued: 01/04/2000
• Est. Priority Date: 10/05/1995
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Sjoberg, Jari, Uitto, Janne, Koski, Ari
• Primary Examiner(s): CHIN, VIVIAN C
• Application Number:
  US08/711,302
• Time in Patent Office: 1,222 Days
• Field of Search: 381/57, 381/103, 381/56, 381/66, 379/406, 379/411
• US Class Current: 381/56
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04M 1/6025 implemented as integrated speech networks

Abstract

The invention relates to equalization in a digital phone, advantageously a mobile phone. According to the invention, the equalization (4) of a reproduced sound is changed according to the operating conditions of the phone. Information about the conditions is obtained by monitoring the sound volume (19) set by the user, measuring the background noise (17) in the operating environment of the phone through the phone'"'"'s microphone (9) and/or monitoring the quality (16) of the connection between the phone and the communication network. The low frequency emphasis is reduced in a very noisy environment and increased in a quiet environment. The telephone according to the invention is advantageously a mobile phone in a digital cellular network.

Claims

1. A method for improving the quality and intelligibility of sound reproduced by a telephone apparatus in which the reproduced sound is handled in a digital form and equalized according to a certain frequency response, wherein there is generated control information describing operating conditions of said telephone apparatus and the frequency response of said equalization is changed on the basis of said control information to optimize the quality and intelligibility of the sound reproduced in a given situation, wherein the telephone apparatus comprises an outgoing channel with a microphone for transmitting an outgoing signal to a distant location and an incoming channel for receiving an incoming signal, the method further comprising steps of:

generating the control information by sensing sound by said microphone at an input to the outgoing channel;

applying said equalization to said incoming signal;

adjusting said equalization in response to the control information obtained by the sensing of the sound at the input to the outgoing channel;

by said microphone, recording the sound to be transmitted via said outgoing channel, measuring noise recorded through said microphone, and employing data representing noise measured by said measuring step for generation of said control information by said generating step; and

by use of voice activity detection means, determining whether or not a user is speaking on the telephone during a call, and conducting said noise measuring step only during those moments when the user is not speaking according to information from said voice activity detection means.

2. The method of claim 1, characterized in that the proportional intensity of a certain frequency area is changed in said equalization, and said changing of the frequency response includes at least one of the following measures:

changing of the gain of said frequency area, changing of the width of said frequency area, changing of the center frequency of said frequency area.

3. The method of claim 1, characterized in that said control information includes a first information element which is formed on the basis of the phone sound volume (19) set by the user.

4. The method of claim 3, characterized in that said first information element describes the gain of the low-frequency part of the sound reproduced, whereby the gain is increased when the user turns the phone sound volume (19) down and the gain is decreased when the user turns the phone sound volume (19) up.

5. The method of claim 1, characterized in that said control information includes a second information element which is formed on the basis of the noise (17) measured in the operating environment of said telephone apparatus.

6. The method of claim 5, characterized in that said second information element describes the gain of the low-frequency part of the sound reproduced, whereby the gain is increased when the measurement shows that the noise (17) in the operating environment is low, and the gain is decreased when the measurement shows that there is a lot of noise (17) in the operating environment.

7. The method of claim 1, characterized in that said control information includes a third information element which is formed on the basis of the quality (16) of the communication connection between said telephone apparatus and the communication network.

8. The method of claim 7, characterized in that said equalization is changed on the basis of said third information element to compensate for the low quality of the communication connection.

9. The method of claim 8, characterized in that said third information element describes the gain of the low-frequency part of the sound reproduced, whereby the gain is increased when the quality (16) of said communication connection is bad, and the gain is decreased when the quality (16) of said communication connection is good.

11. The method of claim 1, characterized in that said control information includes a fourth information element which is formed on the basis of auxiliaries (18) connected to said phone.

10. A method for improving the quality and intelligibility of sound reproduced by a telephone apparatus in which the reproduced sound is handled in a digital form and equalized according to a certain frequency response, wherein there is generated control information describing the operating conditions of said telephone apparatus and the frequency response of said equalization is changed on the basis of said control information to optimize the quality and intelligibility of the sound reproduced in a given situation, the method further comprising recurrently the following steps:

a) without any special temporal order

the first information element is generated according to how the user adjusts the phone sound volume,

it is monitored when the user is not speaking during a call, and the noise in the operating environment of the phone is measured during such moments and the second information element is formed on the basis of the noise measurement,

the quality of the connection between the telephone and the communication networked used via it is monitored and the third information element is formed accordingly, and

b) according to the information elements formed

the gain of the low-frequency part of the sound reproduced is changed inversely proportionally to the sound volume set by the user, whereby value pairs representing a certain sound volume and the corresponding gain form a monotonically falling curve (A;

B;

C;

) in a system of coordinates where the gain is represented as a function of the sound volume setting,

said gain is scaled inversely proportionally to measured noise, whereby said curve shifts downwards (A->

B;

B->

C) in said system of coordinates when the noise increases and upwards (C->

B;

B->

A) when the noise decreases, and

if the connection between the communication network and the phone is bad, said gain of the low-frequency part is set constant, whereby it does not depend on the sound volume setting.

12. A telephone apparatus including a loudspeaker for the reproduction of sound and a digital signal processing means for the digital processing of the sound reproduced, which signal processing means includes an equalizer which has a certain frequency response, wherein said telephone apparatus includes means for the generation of control information describing its operating conditions and a means for changing the frequency response of said equalizer on the basis of said control information, wherein the telephone apparatus comprises:

an outgoing channel for transmitting an outgoing signal to a distant location and an incoming channel for receiving an incoming signal;

means for generating the control information by sensing sound at an input to the outgoing channel, the reproduced sound appearing at an output of the incoming channel, said equalization being applied to said incoming signal;

means for adjusting said equalization in response to the control information obtained by the sensing of the sound at the input to the outgoing channel;

a control block for collecting the data describing said operating conditions and for generating said control information;

a microphone for recording the sound to be transmitted via a telephone connection, noise measuring means for measuring noise recorded through said microphone, and means for conveying data representing noise measured by said measuring means to said control block for the generation of said control information; and

voice activity detection means for determining whether or not a user is speaking on the phone during a call, and said noise measuring means is operative to measure noise only during those moments when the user is not speaking according to the information from said voice activity detection means.

13. The telephone apparatus of claim 12, characterized in that it includes a sound volume adjusting device (19) which can be used by the user and a means for conveying information about the sound volume set with said adjusting device to said control block (15) for the generation of said control information.

14. The telephone apparatus of claim 12, characterized in that said noise measuring means (13;

13a, 13b, 13c) include a weighting filter (13b) which weights noise measurement at certain frequencies.

15. The telephone apparatus of claim 12, characterized in that it includes a means for monitoring the quality (16) of the communication connection between it and the communication network and a means for conveying the information describing the quality of the connection to said control block (15) for the generation of said control information.

16. The telephone apparatus of claim 12, characterized in that it includes a digital signal processor (1) which includes said equalizer (4).

17. The telephone apparatus of claim 16, characterized in that said digital signal processor (1) also includes said control block (15).

18. The telephone apparatus of claim 16, characterized in that said digital signal processor (1) also includes said noise measuring means (13, 13a, 13b, 13c).

19. The telephone apparatus of claim 12, characterized in that it is a mobile phone in a digital cellular network.

20. The telephone apparatus of claim 12, characterized in that it includes a connecting means for the connection of auxiliaries and a means for conveying the information (18) describing the connected auxiliaries to said control block (15) for the generation of said control information.

21. The telephone apparatus of claim 20, characterized in that said auxiliaries include hands-free equipment.

22. A telephone apparatus including a loudspeaker for the reproduction of sound and a digital signal processing means for the digital processing of the sound reproduced, which signal processing means includes an equalizer which has a certain frequency response, wherein said telephone apparatus includes means for the generation of control information describing its operating conditions and a means for changing the frequency response of said equalizer on the basis of said control information;

wherein said equalizer realizes the transfer function ##EQU2## wherein the Zs represent delays of a time unit and said control information comprises variable parameters K, a1 and a2, of which K represents the gain and a1 and a2 represent the center frequency and the bandwidth.

23. A method for improving the quality of sound reproduced by a receiver of a communications system which comprises also a transmitter, the method comprising steps of:

constructing the receiver with a filter having a passband extending across the spectrum of the incoming signal;

measuring ambient sonic noise level at the transmitter by use of a microphone of the transmitter to provide a measurement thereof, and employing the microphone for a transmission of speech from the system;

establishing a plurality of spectral shapes for said passband wherein an individual one of said spectral shapes defines a relationship between amplitude and frequency of a signal transmission characteristic of the filter;

providing a relationship between said spectral shapes and said ambient noise level for signal equalization;

selecting a spectral shape for said passband corresponding to the measurement of the ambient noise level;

generating control information from said measurement of the ambient noise level; and

by use of voice activity detection means, determining whether or not a user is speaking on the telephone during a call, and conducting said noise measuring step only during those moments when the user is not speaking according to information from said voice activity detection means.

24. A method according to claim 23, further comprising steps of:

outputting a sonic signal from said receiver;

providing a relationship between said spectral shapes and a loudness of said sonic signal; and

wherein said selecting step is based both on said relationship between said spectral shapes and said ambient noise level and said relationship between said spectral shapes and said loudness of said sonic signal.

25. A method according to claim 24 wherein the receiver is part of a mobile phone of the communication system.

26. A receiver circuit of a communications system having an incoming signal channel and a transmission signal channel, the receiving circuit serving to improve the quality of sound of an incoming signal reproduced by the receiver circuit in response to a measurement of an ambient noise signal at the transmission channel of the system, the circuit comprising:

a filter with a passband extending across the spectrum of the incoming signal, and being located in the incoming signal channel;

means for measuring ambient sonic noise level at an input to the transmission channel by a microphone of the transmission channel to provide a measurement of the ambient noise level;

means for establishing a plurality of spectral shapes for the passband wherein an individual one of the spectral shapes defines a relationship between amplitude and frequency of a signal transmission characteristic of the filter;

means for providing a relationship between spectral shapes of the passband and said ambient noise level, wherein the passband may have any one of a plurality of said spectral shapes, an individual one of the spectral shapes defining a relationship between amplitude and frequency of a signal transmission characteristic of the filter;

means responsive to the measurement of the ambient noise level for selecting one of said spectral shapes for said passband corresponding to the measurement of the ambient noise level to accomplish signal equalization of said incoming signal; and

voice activity detection means for determining whether or not a user is speaking into the microphone during a call, and said noise measuring means is operative to measure noise only during those moments when the user is not speaking according to the information from said voice activity detection means.

27. A receiver circuit according to claim 26, further comprising:

means for outputting a sonic signal from said receiver;

means for providing a relationship between said spectral shapes and a loudness of said sonic signal; and

wherein said selecting means is responsive both to said relationship between said spectral shapes and said ambient noise level and to said relationship between said spectral shapes and said loudness of said sonic signal.

28. A receiver circuit according to claim 27 wherein the receiver is part of a mobile phone of a communication system.