Sound reproduction system

• US 5,509,081 A
• Filed: 06/07/1995
• Issued: 04/16/1996
• Est. Priority Date: 10/21/1992
• Status: Expired due to Term

• Current Assignee: Nokia Technology GmbH (Nokia Corporation)
• Original Assignee: Nokia Technology GmbH (Nokia Corporation)
• Inventors: Kuusama, Juha
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Lee, Ping W.
• Application Number:
  US08/473,100
• Time in Patent Office: 314 Days
• Field of Search: 381/108, 381/107, 381/106, 381/104, 381/103, 381/86, 381/94, 381/71, 381/68.4, 381/68.2, 381/57
• US Class Current: 381/103
• CPC Class Codes: H03G 3/32 the control being dependent upon ambient noise level or sound level
• CPC Class Codes: H04R 2225/43 Signal processing in hearing aids to enhance the speech intelligibility

Abstract

The invention relates to a sound reproduction system comprising a source of a sound signal in electrical form, a first filter group for dividing the signal derived from the sound signal source into several sound signals occurring in different frequency bands and an adjustable gain amplifier for each frequency band for amplifying the sound signal occurring in said frequency band. To take into account the noise existing in the environment of the sound reproduction system in the adjustment of the system, the system further comprises means for generating an electrical signal proportional to the background noise existing in the environment and means for adjusting the gain of the amplifiers in response to said electrical signal proportional to the background noise.

Claims

1. A sound reproduction system, comprising:

a source (1) of a sound signal in electrical form;

a first filter group (13) for dividing the signal derived from the sound signal source (1) into several electrical sound signals, each electrical sound signal occurring in different frequency bands;

an adjustable gain amplifier for each frequency band for amplifying the electrical sound signal occurring in said frequency band and for providing an electrical sound level signal representing a sound level for each frequency band;

first power level calculation means for each frequency band responsive to said electrical sound level signal for providing a first power level signal (P_audio) indicative of the power level corresponding to the electrical sound level signal for each frequency band;

at least one microphone (3) for generating an electrical total sound signal proportional to the total sound existing in the environment of the sound reproduction system;

another filter group (14) for dividing said electrical total sound signal into several band signals occurring in frequency bands corresponding to the frequency bands of the first filter group (13);

second power level calculation means for each frequency band for determining a second power level signal (P_car) indicative of the power level corresponding to the band signal for each frequency band;

subtraction means for each frequency band for subtracting the first power level signal from the second power level signal occurring in the respective frequency band for generating error signals proportional to the level of background noise existing in the different frequency bands; and

adjustment means for each frequency band for adjusting its amplifier gain in response to a signal proportional to a desired gain value (V) and in response to a signal proportional to the product of said desired gain value and a scaled error signal, said adjustment means for each frequency band including first multiplication means for providing said scaled error signal as the product of said error signal for each frequency band and a gain adjustment signal (EL), the magnitude of said gain adjustment signal (EL) being selected to modify the magnitude of said error signal such that said scaled error signal for each frequency band adjusts the amplifier gain for each frequency band.

2. A sound reproduction system according to claim 1, further comprising:

means for combining the electrical sound level signals for each frequency band for generating an output signal; and

at least one loudspeaker responsive to said output signal for producing sound.

3. A sound reproduction system according to claim 2, further comprising time-delay means for each frequency band for delaying each of the electrical sound level signals for each frequency band prior to being provided to said first power level calculation means for a delay time corresponding to the travel time of sound from said loudspeaker to said microphone.

4. A sound reproduction system according to claim 1, further comprising processing means for each frequency band for eliminating abrupt changes in said error signal prior to being provided to said adjustment means.

5. A sound reproduction system according to claim 1, wherein said adjustment means for each frequency band adjusts said amplifier gain (G) for each adjustable gain amplifier in each frequency band in accordance with the following relationship:

space="preserve" listing-type="equation">G=V{1+EL(P.sub.car -P.sub.audio)}

6. A sound reproduction system according to claim 5, further comprising:

means for combining the electrical sound level signals for each frequency band for generating an output signal; and

at least one loudspeaker responsive to said output signal for producing sound.

7. A sound reproduction system according to claim 6, further comprising time-delay means for each frequency band for delaying each of the electrical sound level signals for each frequency band prior to being provided to said first power level calculation means for a delay time corresponding to the travel time of sound from said loudspeaker to said microphone.

8. A sound reproduction system according to claim 7, further comprising processing means for each frequency band for eliminating abrupt changes in said error signal prior to being provided to said adjustment means.