Automatically variable circuit of sound level of received voice signal in telephone

• US 5,896,450 A
• Filed: 12/06/1995
• Issued: 04/20/1999
• Est. Priority Date: 12/12/1994
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kurihara, Kazuhiro
• Primary Examiner(s): Tsang, Fan S.
• Assistant Examiner(s): Hoosain, Allan
• Application Number:
  US08/568,231
• Time in Patent Office: 1,231 Days
• Field of Search: 379/387, 379/388, 379/390, 379/391, 379/392, 379/389, 381/57, 381/94
• US Class Current: 379/388.03
• CPC Class Codes: H04M 9/08 Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic

Abstract

In an apparatus of adjusting a sound level of a reception voice in a telephone, an audio signal including a transmission voice signal and a peripheral noise is inputted through a microphone. A gain control signal corresponding to a level of the peripheral noise is generated while the transmission voice signal is not present and the gain control signal immediately before input of the transmission voice signal is started is held and outputted while the transmission voice signal is present. A variable gain amplifier amplifies a reception voice signal in accordance with the gain control signal such that a voice corresponding to the reception voice signal is outputted from a speaker with a sound level determined in accordance with the gain control signal.

Claims

1. An apparatus for adjusting a sound level of a reception voice in a telephone, comprising:

a speaker for outputting a reception voice;

a microphone for inputting a transmission voice and a peripheral noise;

a variable gain amplifier for amplifying a reception voice signal in accordance with a gain control signal and driving said speaker in accordance with the amplified reception voice signal such that the reception voice corresponding to said amplified reception voice signal is outputted from said speaker; and

amplifier control means for supplying to said variable gain amplifier as said gain control signal a first signal such that said variable gain amplifier amplifies said reception voice signal in response to said peripheral noise inputted to said microphone when said transmission voice is not inputted for a predetermined time period to said microphone and a second signal such that said variable gain amplifier amplifies said reception voice signal in response to said peripheral noise immediately before the start of said transmission voice while said transmission voice is inputted to said microphone.

2. An apparatus according to claim 1, wherein said amplifier control means includes:

detecting means for detecting an absence or presence of said transmission voice;

gain control signal supplying means for supplying to said variable gain amplifier said first signal as gain control signal determined based on a level of said peripheral noise inputted from said microphone in response to the detection of the absence of said transmission voice by said detecting means for greater than said predetermined time period, and for holding said gain control signal when the input of said transmission voice is started and for supplying the held signal as said second signal to said variable gain amplifier while said transmission voice is inputted.

3. An apparatus according to claim 2, wherein said detecting means includes:

a voice signal band pass filter for passing a voice signal band component of an audio signal inputted from said microphone;

extracting means for extracting an envelope signal of said voice signal band component; and

comparing means for comparing said envelope signal with a predetermined threshold value to detect the presence or absence of the transmission voice.

4. An apparatus according to claim 1, wherein said amplifier control means further includes means for continuing to supply said second signal to said variable gain amplifier during said predetermined time period after the input of said transmission voice is ended.

5. An apparatus according to claim 4, wherein said amplifier control means includes:

detecting means for detecting a presence of said transmission voice signal;

timer means for determining whether said predetermined time period is elapsed after the input of said transmission voice to said microphone is ended; and

gain control signal supplying means for supplying to said variable gain amplifier said first signal as gain control signal determined based on a level of said peripheral noise inputted from said microphone in response to the detection of the absence of said transmission voice by said detecting means after said predetermined time period from the end of input of said transmission voice to said microphone, and for holding said gain control signal when the input of said transmission voice is started and for supplying the held signal as said second signal to said variable gain amplifier while said transmission voice is inputted and during said predetermined time period after the end of input of said transmission voice to said microphone.

6. An apparatus according to claim 5, wherein said detecting means includes:

a voice signal band pass filter for passing a voice signal band component of an audio signal inputted from said microphone;

extracting means for extracting an envelope signal of said voice signal band component; and

comparing means for comparing said envelope signal with a predetermined threshold value to detect the presence or absence of the transmission voice signal.

7. A method of adjusting a sound level of a reception voice in a telephone, comprising the steps of:

inputting an audio signal including a transmission voice signal and a peripheral noise through a microphone;

generating a gain control signal corresponding to a level of said peripheral noise while said transmission voice signal is not present for a predetermined time period and holding said gain control signal immediately before input of said transmission voice signal is started while said transmission voice signal is present; and

amplifying a reception voice signal by a variable gain amplifier in accordance with said gain control signal such that a voice corresponding to said reception voice signal is outputted from a speaker with a sound level determined in accordance with said gain control signal.

8. A method according to claim 7, wherein said generating step includes:

detecting a presence of said transmission voice signal; and

holding said gain control signal in response to the detection of the presence of said transmission voice signal to output said gain control signal held while the presence of said transmission voice signal is detected and outputting said gain control signal in response to said peripheral noise.

9. A method according to claim 8, wherein said detecting step includes:

filtering a voice signal band component from the audio signal;

extracting an envelope signal of said voice signal band component; and

comparing means for comparing said envelope signal with a predetermined threshold value to detect the presence or absence of the transmission voice signal.

10. A method according to claim 7, wherein said outputting step includes:

detecting a presence of said transmission voice signal;

determining whether said predetermined time period is elapsed;

outputting said held gain control signal while said transmission voice signal is present;

outputting said held gain control signal during said predetermined time period after the input of said transmission voice signal is ended; and

outputting said gain control signal in response to said peripheral noise after said predetermined time period.

11. A method according to claim 10, wherein said detecting step includes:

filtering a voice signal band component from the audio signal;

extracting an envelope signal of said voice signal band component; and

comparing said envelope signal with a predetermined threshold value to detect the presence/absence of the transmission voice signal.

12. An apparatus for adjusting a sound level of a reception voice in a telephone, comprising:

a speaker for outputting a reception voice;

a microphone for inputting a transmission voice and a peripheral noise;

a variable gain amplifier for amplifying a reception voice signal in accordance with a gain control signal and driving said speaker in accordance with the amplified reception voice signal such that the reception voice corresponding to said amplified reception voice signal is outputted from said speaker; and

amplifier control means for generating said gain control signal based on the presence or absence of the transmission voice for a predetermined time period and a level of said peripheral noise inputted to said microphone to supply to said variable gain amplifier.

13. An apparatus according to claim 12, wherein said amplifier control means includes:

detecting means for detecting an absence or presence of said transmission voice;

gain control signal supplying means for supplying said gain control signal to said variable gain amplifier such that said variable gain amplifier amplifies said reception voice signal with one of discrete amplification levels determined in accordance with said peripheral noise level when said transmission voice is absent for said predetermined time period and such that said variable gain amplifier amplifies said reception voice signal with a fixed amplification level determined in response to said peripheral noise level immediately before the start of said transmission voice while said transmission voice is present.

14. An apparatus according to claim 13, wherein said detecting means includes:

a voice signal band pass filter for passing a voice signal band component of an audio signal inputted from said microphone;

extracting means for extracting an envelope signal of said voice signal band component; and

comparing means for comparing said envelope signal with a predetermined threshold value to detect the presence or absence of the transmission voice.

15. An apparatus according to claim 12, wherein said amplifier control means further includes means for continuing to supply a fixed gain control signal to said variable gain amplifier during said predetermined time period after the input of said transmission voice is ended.

16. An apparatus according to claim 15, wherein said gain control signal supplying means includes:

detecting means for detecting a presence of said transmission voice signal;

timer means for determining whether said predetermined time period is elapsed after the input of said transmission voice to said microphone is ended; and

gain control signal supplying means for supplying said gain control signal to said variable gain amplifier such that said variable gain amplifier amplifies said reception voice signal with one of discrete amplification levels determined in accordance with said peripheral noise level when said transmission voice is absent and such that said variable gain amplifier amplifies said reception voice signal with a fixed amplification level determined in response to said peripheral noise level immediately before the start of said transmission voice while said transmission voice is present and during said predetermined time period after said transmission voice becomes absent.

17. An apparatus according to claim 15, wherein said fixed gain control signal is the gain control signal immediately before said transmission voice signal becomes present.

18. An apparatus according to claim 15, wherein said detecting means includes:

a voice signal band pass filter for passing a voice signal band component of an audio signal inputted from said microphone;

extracting means for extracting an envelope signal of said voice signal band component; and

comparing means for comparing said envelope signal with a predetermined threshold value to detect the presence or absence of the transmission voice signal.