Equalization contouring by a control curve
A method for equalization contouring provides a reduction of equalization in certain frequency regions either by user control or by automated selection of frequency, without introducing artifacts. A control curve smoothly scales the magnitude of the equalization in the areas where less equalization is desired to obtain a contoured equalization. The control curve varies by frequency and may be defined specifically for every sampled frequency value of the equalization, may be a continuous function of frequency, or may be a function of control points at a select number of frequency points. The control curve may also have automatic inputs, e.g. a machine-detected cutoff frequency of a speaker may be used to determine a control point in the control curve. As another example, the reverberation time (e.g. RT60) may be used to determine a control point in the control curve. The result is a contoured equalization curve without sudden steps.
1. A method for equalization contouring in an audio system comprising:
obtaining a baseline equalization curve stored in a signal processor of the audio system, the baseline equalization curve having a frequency range;
obtaining a control curve defined over the frequency range of the baseline equalization curve;
scaling the baseline equalization curve by the control curve in the signal processor to obtain a contoured equalization;
applying the contoured equalization to an input signal to provide an equalized signal; and
providing the equalized signal to a transducer of the audio system to produce a physical output.
2. The method of claim 1 , wherein the baseline equalization is the magnitude of a result of performing a Fast Fourier Transform (FFT) on a time response of an equalization filter.
3. The method of claim 1 , wherein the baseline equalization is a magnitude, in decibels, of a frequency response of an equalization filter.
4. The method of claim 1 , wherein the control curve is obtained from an interpolation method comprising interpolation between control points defined in a magnitude-frequency mapping.
5. The method of claim 4 , wherein the interpolation method used is linear.
6. The method of claim 4 , wherein the interpolation method used is Bezier interpolation.
7. The method of claim 4 , wherein the interpolation method used is spline interpolation.
8. The method of claim 4 wherein the control points include a highest frequency control point at a highest frequency for which the baseline equalization is defined and a lowest frequency control point at a lowest frequency for which the baseline equalization is defined.
9. The method of claim 4 , wherein a lowest frequency control point is below a lowest frequency for which the baseline equalization is defined or a highest frequency control point is above a highest frequency for which the baseline equalization is defined.
10. The method of claim 9 , wherein the contour curve is zero above the highest frequency control point and is zero below the lowest frequency control point.
11. The method of claim 4 , wherein;
the transducer is at least one audio speaker;
a selected frequency is selectable by a user; and
the control points provide non-zero equalization at frequencies below the selected frequency and zero equalization at the frequencies above the selected frequency.
12. The method of claim 4 , wherein the control points are selected to have a zero magnitude below a lowest frequency of an effective range of the transducer and to have the zero magnitude above a highest frequency of the effective range of the transducer.
13. The method of claim 4 , wherein:
the control points are selected using a reverberation time RT60 to estimate a frequency FR below which the room dominates the response; and
the control points have a magnitude of one at frequencies below the frequency FR and the control points have a magnitude of zero at frequencies above the frequency FR.
14. The method of claim 1 , wherein the baseline equalization curve is a mathematical function of frequency.
15. The method of claim 1 , wherein the control curve is a mathematical function of frequency.
16. The method of claim 1 , wherein the baseline equalization curve corresponds to a room equalization filter.
17. The method of claim 1 , wherein the baseline equalization is derived from an equalization filter stored in a signal processor.
18. A method for equalization contouring in an audio system comprising:
obtaining a baseline equalization curve stored in a signal processor of the audio system, the baseline equalization curve having a frequency range;
obtaining a control curve defined over the frequency range of the baseline equalization curve;
scaling the baseline equalization curve by the control curve in the signal processor to obtain a contoured equalization;
applying the contoured equalization to an input signal to provide an equalized signal; and
providing the equalized signal to an audio transducer of the audio system to produce a sound reproduction signal.
19. A method for equalization contouring in an audio system comprising:
obtaining a baseline equalization curve stored in a signal processor of the audio system, the baseline equalization curve represented as a set of values and a set of corresponding frequencies;
obtaining a set of control curve values defined for the set of corresponding frequencies;
raising each value of the baseline equalization curve to a power derived from a corresponding one of the set of control curve values in the signal processor to obtain a contoured equalization;
applying the contoured equalization to an input signal to provide an equalized signal; and
providing the equalized signal to an audio transducer of the audio system to produce a sound reproduction signal.