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Graphic EQ

Standards-based graphic equalizer

  • Graphic EQ block

Audio Toolbox / Filters


The Graphic EQ block implements a graphic equalizer that can tune the gain on individual octave or fractional octave bands. The block filters the data independently across each input channel over time using the filter specifications. Center frequencies for bands in the graphic equalizer are based on the ANSI S1.11-2004 standard.



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  • Matrix input –– Each column of the input is treated as an independent channel.

  • 1-D vector input –– The input is treated as a signal channel.

Data Types: single | double


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The Graphic EQ block outputs a signal with the same data type as the input signal. The size of the output depends on the size of the input:

  • Matrix input –– The block outputs a matrix the same size and data type as the input signal.

  • 1-D vector input –– The block outputs an N-by-1 matrix (column vector), where N is the number of elements in the 1-D vector input.

Data Types: single | double


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If a parameter is listed as tunable, then you can change its value during simulation.

Specify the order of individual equalizer bands as a positive even integer. All equalizer bands have the same order.

Tunable: Yes

Specify the filter bandwidth as 1 octave, 2/3 octave, or 1/3 octave.

The ANSI S1.11-2004 standard defines the center and edge frequencies of your equalizer. The ISO 266:1997(E) standard specifies corresponding preferred frequencies for labeling purposes.

1-Octave Bandwidth

Center frequencies32 63 126 251 501 1000 1995 3981 7943 15849
Edge frequencies22 45 89 178 355 708 1413 2818 5623 1122 22387
Preferred frequencies31.5 63 125 250 500 1000 2000 4000 8000 16000

2/3-Octave Bandwidth

Center frequencies25 40 63 100 158 251 398 631 1000 1585 2512 3981 6310 10000 15849
Edge frequencies20 32 50 79 126 200 316 501 794 1259 1995 3162 5012 7943 12589 19953
Preferred frequencies25 40 63 100 160 250 400 630 1000 1600 2500 4000 6300 10000 16000

1/3-Octave Bandwidth

Center frequencies25 32 40 50 63 79 100 126 158 200 251 316 398 501 631 794 1000 1259 1585 1995 2512 3162 3981 5012 6310 7943 10000 12589 15849 19953
Edge frequencies22 28 35 45 56 71 89 112 141 178 224 282 355 447 562 708 891 1122 1413 1778 2239 2818 3548 4467 5623 7079 8913 11220 14125 17783 22387
Preferred frequencies25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 12500 16000 20000

Tunable: No

Specify the type of implementation as Cascade or Parallel. See Algorithms and Graphic Equalization for information about these implementation structures.

Tunable: No

Specify the gain of each octave or fractional octave band in dB. The number and position of filters in the graphic equalizer depends on the Bandwidth parameter.

Tunable: Yes

Name of the variable in the base workspace to contain the filter when it is exported. The name must be a valid MATLAB® variable name.

When you select this parameter, exporting the filter overwrites the variable specified by the Variable name parameter if it already exists in the base workspace. If you do not select this parameter and the specified variable already exists in the workspace, exporting the filter creates a new variable with an underscore and a number appended to the variable name. For example, if the variable name is var and it already exists, the exported variable will be named var_1.

Export the filter to the base workspace in the variable specified by the Variable name parameter.


You cannot export the filter if you have enabled the Inherit sample rate from input parameter and the model is not running.

When you select this parameter, the block inherits its sample rate from the input signal. When you clear this parameter, specify the sample rate in Input sample rate (Hz).

Tunable: No

Tunable: Yes


To enable this parameter, clear the Inherit sample rate from input parameter.

  • Interpreted execution –– Simulate model using the MATLAB interpreter. This option shortens startup time and has simulation speed comparable to Code generation. In this mode, you can debug the source code of the block.

  • Code generation –– Simulate model using generated C code. The first time you run a simulation, Simulink® generates C code for the block. The C code is reused for subsequent simulations, as long as the model does not change. This option requires additional startup time but the speed of the subsequent simulations is faster than Interpreted execution.

Tunable: No

Block Characteristics

Data Types

double | single

Direct Feedthrough


Multidimensional Signals


Variable-Size Signals


Zero-Crossing Detection



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The implementation of your graphic equalizer depends on the Structure parameter. See Graphic Equalization for a discussion of the pros and cons of the parallel and cascade implementations. Refer to the following sections to understand how these algorithms are implemented in Audio Toolbox™.


[1] Oliver, Richard J., and Jean-Marc Jot. "Efficient Multi-Band Digital Audio Graphic Equalizer with Accurate Frequency Response Control." Presented at the 139th Convention of the AES, New York, October 2015.

[2] Acoustical Society of America. American National Standard Specification for Octave-Band and Fractional-Octave-Band Analog and Digital Filters. ANSI S1.11-2004. Melville, NY: Acoustical Society of America, 2009.

[3] International Organization for Standardization. Acoustics –– Preferred frequencies. ISO 266:1997(E). Second Edition. 1997.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2017b