Electrical audio signal processing systems and devices – Feedback suppression
Reexamination Certificate
1997-09-30
2001-02-27
Isen, Forester W. (Department: 2747)
Electrical audio signal processing systems and devices
Feedback suppression
C379S406010
Reexamination Certificate
active
06195437
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to computer systems having a microphone and a loudspeaker, and more particularly, to computer systems providing a speakerphone mode and non-speakerphone audio modes.
2. Description of the Related Art
Often in a computer system, a loudspeaker and microphone are turned on for various modes of a computer system such as a speakerphone mode or non-speakerphone audio modes. Examples of non-speakerphone audio modes include a recording mode, a playback mode, and an idle mode. When both the microphone and loudspeaker are turned on but not in use, noise has been generated and amplified by the acoustic loop formed by the microphone and loudspeaker. In a speakerphone mode of a computer system, an automatic gain control circuit of a digital signal processor has been used to reduce the gain in the acoustic loop thereby eliminating such noise. However, in a non-speakerphone audio mode of a computer system, a digital signal processor is not included in the acoustic or microphone path of the computer system. Since the automatic gain control circuit of the digital signal processor is not within the microphone path of a computer system during a non-speakerphone audio mode, noise is undesirably generated and amplified by the acoustic loop formed by the microphone and loudspeaker in a non-speakerphone audio mode.
The amplified noise is received and acoustically transmitted by the loudspeaker. Since the loudspeaker is acoustically coupled to the microphone, the amplified noise returns again to the microphone and is again amplified by the acoustic loop formed by the microphone and loudspeaker. The microphone and loudspeaker of the computer system thus are placed into a feedback loop of a high gain, rendering the computer system acoustically unstable. The resulting acoustic feedback is manifested to a user as an irritating whining or screaming noise.
When the acoustic feedback takes the form of this irritating whining noise, the computer user may be operating other applications of the computer system such that the source of the noise is hidden or not apparent to the user. The user therefore is required to interrupt its use of these applications in an effort to determine the source and cause of the irritating noise. Such a determination is particularly challenging to a user where the user has exited the particular software application in which the microphone and loudspeaker were turned on.
Moreover, the hidden problem of feedback noise generated in a non-speakerphone audio mode of a computer system is propounded by a microphone path of a computer system which maximizes gain for a speakerphone mode of a computer system. In a conventional computer system having a speakerphone mode and non-speakerphone audio modes, the gain of the microphone path in the computer system during a speakerphone mode is interdependent with the gain of the microphone path in the computer system during non-speakerphone audio modes. Therefore, a computer system having an acoustic path which maximizes gain for a speakerphone mode necessarily maximizes gain for non-speakerphone audio modes as well. During a speakerphone mode of a computer system, users commonly add gain to the microphone path of a computer system through an audio mixer chip to improve the signal-to-noise ratio of sound radiated by the loudspeaker. While a maximization of acoustic gain for a speakerphone mode optimizes acoustic performance, a maximization of acoustic gain for a non-speakerphone audio mode is a maximization of undesirable acoustic feedback. Thus, even if the hidden problem of acoustic feedback noise associated with a non-speakerphone audio modes were known to a user, the user would still be confronted with a tradeoff between maximizing acoustic gain for a speakerphone mode of the computer system and minimizing acoustic gain for non-speakerphone audio modes of the computer system.
SUMMARY OF THE INVENTION
Briefly, the present invention provides a method and apparatus for controlling acoustic gain during a non-speakerphone audio mode of a computer system independent of acoustic gain during a speakerphone mode of the computer system. BIOS code within a non-volatile memory of the computer system detects whether the computer system is in a speakerphone mode or a non-speakerphone audio mode. If the computer system is in a non-speakerphone audio mode, a predetermined upper limit is placed on the gain in the microphone path of the computer system. In this way, the problem of acoustic feedback noise due to high gain in the microphone path of the computer system is eliminated. If the computer system is in a speakerphone mode, an upper limit is not provided for the gain in the microphone path of the computer system, allowing for maximization of gain which optimizes acoustic performance during a speakerphone mode.
In one embodiment of the present invention, the predetermined upper gain limit is applied at a microphone pre-amplifier present in the microphone path of the computer system. Application of the predetermined upper gain limit at the microphone pre-amplifier is controlled by gain control logic coupled to the microphone pre-amplifier. In an alternative embodiment of the present invention, the predetermined upper gain limit is applied at an audio mixer chip present in the microphone path of the computer system during a non-speakerphone audio mode. Application of the predetermined upper gain limit at the audio mixer chip is controlled by a driver which communicates with the audio mixer chip.
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Ford Jeremy
Gong Ji-An
Markow Mitchell A.
Akin Gump Strauss Hauer & Feld & LLP
Compaq Computer Corporation
Isen Forester W.
Pendleton Brian Tyrone
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