Automatic loudspeaker equalizer

• US 6,721,428 B1
• Filed: 11/13/1998
• Issued: 04/13/2004
• Est. Priority Date: 11/13/1998
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Allred, Rustin W., Tsecouras, Michael, Young, Robert S. Jr.
• Primary Examiner(s): Nguyen, Duc
• Assistant Examiner(s): LAO, LUNSEE
• Application Number:
  US09/191,944
• Time in Patent Office: 1,978 Days
• Field of Search: 381/56, 381/57, 381/58, 381/59, 381/103, 381/107, 381/97, 700/94, 708/322.F
• US Class Current: 381/103
• CPC Class Codes: H03G 5/005 of digital signals
• CPC Class Codes: H03G 5/165 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H04R 29/001 for loudspeakers H04R29/007 takes precedence
• CPC Class Codes: H04R 3/04 for correcting frequency response
• CPC Class Codes: H04S 7/30 Control circuits for electronic adaptation of the sound field

Abstract

A method for generating digital filters for equalizing a loudspeaker. First digital data is provided, for a tolerance range for a target response curve of sound level versus frequency for the loudspeaker. Second digital data is generated, for an actual response curve of sound level versus frequency for the loudspeaker. The first digital data is compared with the second digital data and it is determined whether the actual response curve is within the tolerance range. If the actual response curve is not within the tolerance range, digital audio filters are iteratively generated, and the digital audio filters are applied to the second digital data to generate third digital data for a compensated response curve. The frequency, amplitude and bandwidth of the digital audio filters are automatically optimized until the compensated response curve is within the tolerance range or a predetermined limit on the number of digital audio filters has been reached, whichever occurs first.

Claims

1. A method for generating digital filters for equalizing a loudspeaker, comprising the steps of:

providing first digital data for a tolerance range for a target response curve of sound level versus frequency for said loudspeaker;

providing second digital data for an actual response curve of sound level versus frequency for said loudspeaker;

comparing said first digital data to said second digital data and determining whether said actual response curve is within said tolerance range; and

if said actual response curve is not within said tolerance range,

iteratively generating digital audio filters,

generating modified data relating to the response of said loudspeaker modified by said digital audio filters, and

automatically optimizing the frequency, amplitude and bandwidth of said digital audio filters until said modified data is within said tolerance range or a predetermined limit on the number of digital audio filters has been reached, whichever occurs first.

2. A method according to claim 1, wherein

said step of generating modified data is performed by applying said digital audio filters to said second digital data to generate third digital data for a compensated response curve; and

said step of automatically optimizing the frequency, amplitude and bandwidth is performed by automatically optimizing the frequency, amplitude and bandwidth of said digital audio filters until said compensated response curve is within said tolerance range or a predetermined limit on the number of digital audio filters has been reached, whichever occurs first.

3. A method according to claim 1, wherein said step of generating modified data is performed by applying said digital audio filters and measuring the resulting response curve of sound level versus frequency for said loudspeaker.

4. A method according to claim 1, wherein said step of iteratively generating digital audio filters is performed by iteratively generating second-order filters.

5. A method for generating a set of second order filters to equalize a loudspeaker, comprising the steps of:

providing first digital data for a tolerance range for a target response curve of sound level versus frequency for said loudspeaker;

providing second digital data for an actual response curve of sound level versus frequency for said loudspeaker;

comparing said first digital data to said second digital data and determining whether said actual response curve is within said tolerance range; and

if said actual response curve is not within said tolerance range, generating a set of filters to equalize said loudspeaker by performing the following optimizing steps iteratively,

digitally processing said second digital data to determine an n^th set of initial parameters for an n^th peak in said actual response curve where said actual response curve is not within said tolerance range, including a frequency, and amplitude and a bandwidth for said peak, where n is the number of an iteration of said optimizing steps,

digitally generating a compensating n^th filter from said n^th set of initial parameters,

applying said n^th filter to said second digital data and modifying said n^th set of initial parameters to determine an n^th set of optimum parameters for said compensating n^th filter, to generate third digital data for an n^th interim compensated response curve of sound level versus frequency,

processing said third digital data to determine whether said n^th interim compensated response curve is within said tolerance range,

if said n^th interim compensated response curve is not within said tolerance range, performing another iteration of said optimizing steps until said interim compensated response curve is within said tolerance range or a predetermined limit on the number of filters has been reached, whichever occurs first.

6. A method according to claim 5, wherein said step of digitally generating a compensating n^th filter is performed by digitally generating a second-order filter.

7. A method for generating filters for equalizing a loudspeaker, comprising the steps of:

providing first digital data for a tolerance range for a target response curve of sound level versus frequency for said loudspeaker;

providing second digital data for an actual response curve of sound level versus frequency for said loudspeaker;

comparing said first digital data to said second digital data and determining whether said actual response curve is within said tolerance range; and

if said actual response curve is not within said tolerance range, generating a set of compensating filters by performing the following single filter optimizing steps iteratively,

digitally processing said second digital data to determine an n^th set of initial parameters for an n^th peak in said actual response curve where said actual response curve is not within said tolerance range, including a frequency, an amplitude and a bandwidth for said peak, where n is the number of an iteration of said optimizing steps,

digitally generating a compensating n^th filter from said n^th set of initial parameters,

applying said n^th filter to said second digital data and modifying said n^th set of initial parameters to determine an n^th set of optimum parameters for said n^th filter, to generate third digital data for an n^th interim compensated response curve of sound level versus frequency;

if n>

1, performing the following joint filter optimizing steps iteratively and cyclically,

generating fourth digital data for interim computed response curves in which for each joint filter optimizing iteration one of said n filters is absent, and then performing said single filter optimization steps utilizing said fourth digital data to generate fifth digital data for an updated interim response curve,

digitally processing said fifth digital data to determine whether the most recent of said joint filter optimizing iterations has resulted in a change in said updated interim response curve greater than a predetermined amount of change, and if so continuing to perform said joint filter optimizing steps;

processing said fifth digital data to determine whether said n^th interim compensated response curve is within said tolerance range,

and if not,

performing another iteration of the foregoing steps until said interim compensated response curve is within said tolerance range or a predetermined limit on the number of filters has been reached, whichever occurs first,

but if so, ceasing performance of further iterations.

8. A method according to claim 7, wherein said step of digitally generating a compensating n^th filter is performed by digitally generating a second-order filter.

9. A method for generating filters for equalizing a loudspeaker, comprising the steps of:

providing a source of first audio digital data;

providing a digital audio processing unit for processing said first audio digital data and providing processed audio digital data, including applying digital audio filters for equalizing said loudspeaker characterized by coefficients in algorithms applied to said first audio digital data to effect said digital audio filters;

providing a digital to analog converter for converting said processed audio digital data to an analog audio signal for provision to said loudspeaker;

providing a sound field measuring device in the vicinity of said loudspeaker to generate second audio digital data representing sound produced by said loudspeaker;

providing a digital computer connected to receive said second audio digital data, and programming said digital computer to determine said coefficients for digital filters for equalizing a loudspeaker and provide said coefficients to said digital audio processing unit by

providing third digital data for a tolerance range for a target response curve of sound level versus frequency for said loudspeaker;

providing said second digital data, wherein said second digital data represents an actual response curve of sound level versus frequency for said loudspeaker;

comparing said third digital data to said second digital data and determining whether said actual response curve is within said tolerance range; and

if said actual response curve is not within said tolerance range,

iteratively generating digital audio filters by iteratively generating coefficients for said digital audio filters, applying said digital audio filters determined by said coefficients to said second digital data to generate fourth digital data for a compensated response curve, and

automatically optimizing said coefficients until said compensated response curve is within said tolerance range or a predetermined limit on the number of digital audio filters has been reached, whichever occurs first.

10. An method according to claim 9, wherein said digital computer is programmed to determine said coefficients by

automatically optimizing said coefficients by optimizing the frequency, amplitude and bandwidth of said digital audio filters.

11. An apparatus for generating filters for equalizing a loudspeaker, comprising:

a source of first audio digital data;

a digital audio processing unit for processing said first audio digital data and providing processed audio digital data, including applying digital audio filters for equalizing said loudspeaker characterized by coefficients in algorithms applied to said first audio digital data to effect said digital audio filters;

a digital to analog converter for converting said processed audio digital data to an analog audio signal for provision to said loudspeaker;

a sound field measuring device in the vicinity of said loudspeaker to generate second audio digital data representing sound produced by said loudspeaker;

a digital computer connected to receive said second audio digital data, and programmed to determine said coefficients for digital filters for equalizing a loudspeaker and provide said coefficients to said digital audio processing unit, said digital computer being programmed to determine said coefficients by

providing third digital data for a tolerance range for a target response curve of sound level versus frequency for said loudspeaker;

providing said second digital data, wherein said second digital data represents an actual response curve of sound level versus frequency for said loudspeaker;

comparing said third digital data to said second digital data and determining whether said actual response curve is within said tolerance range; and

if said actual response curve is not within said tolerance range,

iteratively generating digital audio filters by iteratively generating coefficients for digital audio filters, applying digital audio filters determined by said coefficients to said second digital data to generate fourth digital data for a compensated response curve, and

automatically optimizing said coefficients until said compensated response curve is within said tolerance range or a predetermined limit on the number of digital audio filters has been reached, whichever occurs first.

12. An apparatus according to claim 11, wherein said digital computer is programmed to determine said coefficients by

automatically optimizing said coefficients by optimizing the frequency, amplitude and bandwidth of said digital audio filters.

13. A method for generating digital filters for equalizing a loudspeaker, comprising the steps of:

providing first digital data for a tolerance range for a target response curve of sound level versus frequency for said loudspeaker;

providing second digital data for a first actual response curve of sound level versus frequency for said loudspeaker;

comparing said first digital data to said second digital data and determining whether said first actual response curve is within said tolerance range; and

if said first actual response curve is not within said tolerance range,

iteratively generating digital audio filters to compensate said actual response curve,

applying said digital audio filters to said first digital data to generate third digital data, converting said third digital data to an analog signal and providing said analog signal to said loudspeaker,

generating fourth digital data for a second actual response curve of sound level from said analog signal versus frequency for said loudspeaker;

comparing said first digital data to said fourth digital data and determining whether said second actual response curve is within said tolerance range; and

automatically optimizing the frequency, amplitude and bandwidth of said digital audio filters until said second actual response curve is within said tolerance range or a predetermined limit on the number of digital audio filters has been reached, whichever occurs first.

14. A method according to claim 13, wherein said step of iteratively generating digital audio filters is performed by iteratively generating second-order filters.

15. A method for generating total log-integral metric digital data for characterizing the perceived performance of a loudspeaker, comprising the steps of:

providing first digital data for N samples for a desired response curve of sound level versus frequency for said loudspeaker;

providing second digital data for N samples for an actual response curve of sound level versus frequency for said loudspeaker; and

generating total log-integral metric data according to the formula;

$M=\underset{i=1}{\overset{N-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\log }_{10}<br><br>\left(\frac{f_{i+1}}{f_i}\right)<br><br>\left[\frac{<br><br>{S<br><br>\left(f_i\right)}_{d<br><br>\text{\hspace{1em}<br><br>}<br><br>B}-{D<br><br>\left(f_i\right)}_{d<br><br>\text{\hspace{1em}<br><br>}<br><br>B}<br><br>+<br><br>{S<br><br>\left(f_{i+1}\right)}_{d<br><br>\text{\hspace{1em}<br><br>}<br><br>B}-{D<br><br>\left(f_{i+1}\right)}_{d<br><br>\text{\hspace{1em}<br><br>}<br><br>B}<br><br>}{2}\right]$

 

where;

M is the total log-integral metric,

f is the frequency,

D is the first digital data,

S is the second digital data, and

N is the number of samples of first digital data and of second digital data.

16. A method for generating digital filters for equalizing a plurality of loudspeakers, comprising the steps of:

providing first digital data for a tolerance range for a target response curve of sound level versus frequency for said loudspeakers;

providing second digital data for an actual response curve of sound level versus frequency for said loudspeakers;

comparing said first digital data to said second digital data and determining whether said actual response curve is within said tolerance range; and

if said actual response curve is not within said tolerance range,

iteratively generating digital audio filters,

applying said digital audio filters to said second digital data to generate third digital data for a compensated response curve, and automatically optimizing the frequency, amplitude and bandwidth of said digital audio filters until said compensated response curve is within said tolerance range or a predetermined limit on the number of digital audio filters has been reached, whichever occurs first.