Graphic EQ

Standards-based graphic equalizer

• 

Libraries:
Audio Toolbox / Filters

Description

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.

Examples

Perform Graphic Equalization

Examine the Graphic EQ block in a Simulink® model and tune parameters.

• Open Model

Ports

Input

Port_1 — Input signal

matrix | 1-D vector

• 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

Output

Port_1 — Output signal

matrix

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

Parameters

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

EQ Order — Order of individual equalizer bands

2 (default) | positive even integer

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

Tunable: Yes

Bandwidth — Filter bandwidth (octaves)

1 octave (default) | 2/3 octave | 1/3 octave

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 frequencies	32 63 126 251 501 1000 1995 3981 7943 15849
Edge frequencies	22 45 89 178 355 708 1413 2818 5623 1122 22387
Preferred frequencies	31.5 63 125 250 500 1000 2000 4000 8000 16000

2/3-Octave Bandwidth

Center frequencies	25 40 63 100 158 251 398 631 1000 1585 2512 3981 6310 10000 15849
Edge frequencies	20 32 50 79 126 200 316 501 794 1259 1995 3162 5012 7943 12589 19953
Preferred frequencies	25 40 63 100 160 250 400 630 1000 1600 2500 4000 6300 10000 16000

1/3-Octave Bandwidth

Center frequencies	25 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 frequencies	22 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 frequencies	25 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

Structure — Type of implementation

Cascade (default) | Parallel

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

Tunable: No

Gains — Gain of each octave or fractional octave band (dB)

0 | scalar

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

Variable name — Variable name of exported filter

myFilt (default) | valid variable name

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.

Overwrite variable if it already exists — Overwrite variable if it already exists

on (default) | off

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 filter to workspace — Export filter to workspace

button

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

Tips

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

Inherit sample rate from input — Specify source of input sample rate

off (default) | on

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

Input sample rate (Hz) — Sample rate of input

44100 (default) | scalar

Tunable: Yes

Dependencies

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

Simulate using — Specify type of simulation to run

Code generation (default) | Interpreted execution

• 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	no
Multidimensional Signals	no
Variable-Size Signals	yes
Zero-Crossing Detection	no

Algorithms

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™.

Parallel Structure

Filter Bank Design

The parallel implementation designs the individual equalizers using the octaveFilter design method and spaces them on the spectrum according to the ANSI S1.11-2004 standard.

If you set the Input sample rate (Hz) parameter so that the Nyquist frequency (Input sample rate (Hz)/2) is less than the final bandpass edge defined by the ANSI S1.11-2004 standard, then:

• The final bandpass filter is the one whose upper bandpass edge is less than the Nyquist frequency.

• The final filter is implemented as a highpass filter designed by the designParamEQ function.

Real-Time Computation

1. The input signal is fed into a filterbank of M filters, where M depends on the specified Bandwidth and Input sample rate (Hz) parameters.

2. Each branch of the filterbank is multiplied by the linear form of the corresponding element of the Gains parameter.

3. The branches are summed and the output signal is returned.

Cascade Structure

Filter Bank Design

The cascade implementation designs the graphic equalizer filter bank using the multibandParametricEQ System object™.

Gain Setting

If the EQ Order parameter is set to 2, then a gain correction is calculated according to [1]. The gain correction is independent of the requested gains. The gain correction is recomputed during the real-time processing only if the Input sample rate (Hz) parameter is modified.

If the EQ Order parameter is not set to 2, no gain correction is applied and the requested gains are passed on to the multibandParametricEQ object.

Real-Time Computation

The input signal is fed into a cascade of M biquad filters, where M depends on the specified Bandwidth and Input sample rate (Hz) parameters.

References

[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