Weighting Filter

Weighted frequency response filter

• 

Libraries:
Audio Toolbox / Filters

Description

The Weighting Filter block performs frequency-weighted filtering independently across each input channel.

Examples

Apply Frequency Weighting

Examine the Weighting Filter block in a Simulink® model and tune parameters.

• Open Script

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 single channel.

Data Types: single | double

Output

Port_1 — Output signal

matrix

The Weighting Filter 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.

Data Types: single | double

Parameters

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

Weighting method — Type of frequency weighting

A-weighting (default) | C-weighting | K-weighting

See A-Weighting, C-Weighting, and K-Weighting for the definition of the weighting curves.

Tunable: No

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, you specify the sample rate in Input sample rate (Hz).

Tunable: No

Input sample rate (Hz) — Sample rate of input

44100 (default) | positive 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

• 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.

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

Tunable: No

Mask for attenuation limits — Creates a mask for filter response visualization

No mask (default) | Class 1 | Class 2

The mask attenuation limits are defined in the IEC 61672-1:2002 standard.

• If the mask is green, the design is compliant.

• If the mask is red, the design breaks compliance.

Tunable: Yes

Dependencies

To enable this parameter, set Weighting method to A-weighting or C-weighting.

Visualize filter response — Open plot to visualize magnitude response and compliance mask

button

A 2048-point FFT is used to calculate the magnitude response.

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.

Block Characteristics

Data Types	double | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	yes
Zero-Crossing Detection	no

More About

A-Weighting

The A-curve is a wide bandpass filter centered at 2.5 kHz, with approximately 20 dB attenuation at 100 Hz and 10 dB attenuation at 20 kHz. A-weighted SPL measurements of noise level are increasingly found in sales literature for domestic appliances. In most countries, the use of A-weighting is mandated for the protection of workers against noise-induced deafness. The ISO and ICOA standards mandate A-weighting for all civil aircraft noise measurements.

The ANSI S1.42.2001 [1] defines this weighting curve. The IEC 61672-1:2002 [2] standard defines the minimum and maximum attenuation limits for an A-weighting filter.

ANSI S1.42.2001 defines the weighting curve by specifying analog poles and zeros. Audio Toolbox™ converts the specified poles and zeros to the digital domain using a bilinear transform:

C-Weighting

The C-curve is "flat," but with limited bandwidth: It has –3 dB corners at 31.5 Hz and 8 kHz. C-curves are used in sound level meters for sounds that are louder than sounds intended for A-weighting filters.

The ANSI S1.42-2001 [1] defines the C-weighting curve. The IEC 61672-1:2002 [2] standard defines the minimum and maximum attenuation limits for C-weighting filters.

ANSI S1.42.2001 defines the weighting curve by specifying analog poles and zeros. Audio Toolbox converts the specified poles and zeros to the digital domain using a bilinear transform:

K-Weighting

The K-weighting filter is used for loudness normalization in broadcast. It is composed of two stages of filtering: a first stage shelving filter and a second stage highpass filter.

The ITU-R BS.1770-4 [3] standard defines this curve.

Assume a second-order filter.

The table shows the coefficients for the filters.

First Stage Shelving Coefficients	Second Stage Highpass Coefficients
$$a_1=-1.69065929318241$$	$$a_1=-1.99004745483398$$
$$a_2=0.73248077421585$$	$$a_2=0.99007225036621$$
$$b_0=1.53512485958697$$	$$b_0=1.0$$
$$b_1=-2.6916918940638$$	$$b_1=-2.0$$
$$b_2=1.19839281085285$$	$$b_2=1.0$$

The coefficients presented by ITU-R BS.1770-4 are defined for 48 kHz. These coefficients are recomputed for nonstandard sample rates using the algorithm described in [4].

References

[1] Acoustical Society of America. Design Response of Weighting Networks for Acoustical Measurements. ANSI S1.42-2001. New York, NY: American National Standards Institute, 2001.

[2] International Electrotechnical Commission. Electroacoustics Sound Level Meters Part 1: Specifications. First Edition. IEC 61672-1. 2002-2005.

[3] International Telecommunication Union. Algorithms to measure audio programme loudness and true-peak audio level. ITU-R BS.1770-4. 2015.

[4] Mansbridge, Stuart, Saoirse Finn, and Joshua D. Reiss. "Implementation and Evaluation of Autonomous Multi-track Fader Control." Paper presented at the 132nd Audio Engineering Society Convention, Budapest, Hungary, 2012.

Extended Capabilities

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

Version History

Introduced in R2016b