Adjusting dynamic range of an audio system

• US 8,229,125 B2
• Filed: 02/06/2009
• Issued: 07/24/2012
• Est. Priority Date: 02/06/2009
• Status: Active Grant

• Current Assignee: Bose Corporation
• Original Assignee: Bose Corporation
• Inventors: Short, William R.
• Primary Examiner(s): Pham, Thanh V
• Application Number:
  US12/367,095
• Publication Number:
  US 20100202631A1
• Time in Patent Office: 1,264 Days
• Field of Search: 381/56, 381/57, 381/58, 381/104, 381/108
• US Class Current: 381/56
• CPC Class Codes: H03G 3/32 the control being dependent upon ambient noise level or sound level
• CPC Class Codes: H03G 7/002 in untuned or low-frequency amplifiers, e.g. audio amplifiers H03G7/007, H03G7/001, H03G7/008, H03G7/02, H03G7/06 take precedence
• CPC Class Codes: H03G 9/025 frequency-dependent volume compression or expansion, e.g. multiple-band systems H03G9/10, H03G9/18 take precedence

Abstract

An audio reproduction system substantially fits the dynamic range of recorded and broadcast music (or other type of audio content) into a desired output dynamic range, bounded by the available dynamic range of the listening environment. In some scenarios the output dynamic range may be defined as a function of the ambient noise level present in the environment and the maximum output capabilities of audio system. A listener may adjust the desired prominence of the program with a user control, with foreground (louder and more dynamic) as one extreme and background (quieter and less dynamic) as the other extreme. A control to adjust prominence, when used to provide background reproduction, may reduce the average volume of a reproduced signal and fit the input signal dynamic range into a suitably smaller but desired output signal dynamic range.

Claims

1. A method of adjusting a dynamic range of an audio system comprising:

providing an audio system that includes variable values for at least the following parameters;

(i) an output signal dynamic range, (ii) a maximum output signal level, and (iii) a minimum output signal level;

receiving a user specified value for at least a first of the parameters;

determining a value of a second of the parameters, wherein the determined value of the second parameter is based at least in part on the user-specified value of the first parameter, and

applying a gain to an input signal as a function of time to compress the input signal to fit within a value set for the output signal dynamic range parameter, wherein the input signal is divided into a plurality of frequency bands and a gain is applied to the input signal in each frequency band to compress the input signal to fit within an output signal dynamic range set for each frequency band, and wherein the gain applied to each frequency band is adjusted by a negative feedback servo loop wherein the servo loop computes the time average of the gains, scales the time averaged gains, and subtracts the scaled, time averaged gains from the gains applied to each frequency band, to reduce tilt across frequency of the long term average gains of individual frequency bands.

2. The method of claim 1 wherein the first parameter specified by the user is the maximum output signal level.

3. The method of claim 1 wherein first parameter specified by the user is the output signal dynamic range.

4. The method of claim 1 wherein the minimum output signal level is based on the level of ambient noise present in the listening environment.

5. The method of claim 4 wherein the level of ambient noise present in the environment is either directly sensed by a microphone or is estimated.

6. The audio system of claim 4 wherein the level of ambient noise present in the environment is either directly sensed by a microphone or is estimated.

7. The method of claim 1 in which the feedback signal is based on averaging applied gains across adjacent frequency ranges.

8. The audio system of claim 1 wherein the first parameter specified by the user is the maximum output signal level.

9. The audio system of claim 1 wherein first parameter specified by the user is the output signal dynamic range.

10. The audio system of claim 1 wherein the minimum output signal level is based on the level of ambient noise present in the listening environment.

11. A method for controlling operation of an audio system comprising:

Simultaneously controlling with a single control two of the following three parameters;

(i) an output signal dynamic range, (ii) a maximum output signal level, and (iii) a minimum output signal level.

12. The method of claim 11 wherein the output signal dynamic range and the maximum output signal level are simultaneously controlled.

13. An apparatus for controlling operation of an audio system comprising:

a single control that simultaneously controls two of the following three parameters;

(i) an output signal dynamic range, (ii) a maximum output signal level, and (iii) a minimum output signal level.

14. The method of claim 13 wherein the controller simultaneously controls the output signal dynamic range and the maximum output signal level.

15. An audio system comprising:

a user control for receiving a user specified value for at least one of a plurality of parameters consisting of (i) an output signal dynamic range, (ii) a maximum output signal level, and (iii) a minimum output signal level;

a processor for determining a value of a second of the parameters, wherein the determined value of the second parameter is based at least in part on the user-specified value of the first parameter, and

gain determining elements for determining a gain to apply to an input signal to compress the input signal to fit within a value set for the output signal dynamic range parameter, wherein the gain is a function of time, to divide the input signal into a plurality of frequency bands, to apply a gain to the input signal in each frequency band to compress the input signal to fit within an output signal dynamic range set for each frequency band, and

a negative feedback servo loop to adjust computes the time average of the gains, scales the time averaged gains, and subtracts the scaled, time averaged gains from the gains applied to each frequency band, to reduce tilt across frequency of the long term average gains of individual frequency bands.