Crossover Filter

Audio crossover filter

• Library:

• Audio Toolbox / Filters

• 

Description

The Crossover Filter block implements an audio crossover filter, which is used to split an audio signal into two or more frequency bands. Crossover filters are multiband filters whose overall magnitude frequency response is flat.

Ports

Input

x — 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.

This port is unnamed unless you specify additional input ports.

Data Types: single | double

F1 — Crossover frequency (Hz)

real scalar in the range 20 to 20000

Dependencies

To enable this port, select Specify from input port for the Crossover frequency (Hz) parameter.

Data Types: single | double

O1 — Crossover order

integer in the range 0 to 8

Dependencies

To enable this port, select Specify from input port for the Crossover order parameter.

Data Types: single | double

F2 — Crossover frequency (Hz)

real scalar in the range 20 to 20000

Dependencies

To enable this port, you need to both:

• Select Specify from input port for the Crossover frequency (Hz) parameter.

• Set Number of crossovers to 2, 3 or 4.

Data Types: single | double

O2 — Crossover order

integer in the range 0 to 8

Dependencies

To enable this port, you need to both:

• Select Specify from input port for the Crossover order parameter.

• Set Number of crossovers to 2, 3 or 4.

Data Types: single | double

F3 — Crossover frequency (Hz)

real scalar in the range 20 to 20000

Dependencies

To enable this port, you need to both:

• Select Specify from input port for the Crossover frequency (Hz) parameter.

• Set Number of crossovers to 3 or 4.

Data Types: single | double

O3 — Crossover order

integer in the range 0 to 8

Dependencies

To enable this port, you need to both:

• Select Specify from input port for the Crossover order parameter.

• Set Number of crossovers to 3 or 4.

Data Types: single | double

F4 — Crossover frequency (Hz)

real scalar in the range 20 to 20000

Dependencies

To enable this port, you need to both:

• Select Specify from input port for the Crossover frequency (Hz) parameter.

• Set Number of crossovers to 4.

Data Types: single | double

O4 — Crossover order

integer in the range 0 to 8

Dependencies

To enable this port, you need to both:

• Select Specify from input port for the Crossover order parameter.

• Set Number of crossovers to 4.

Data Types: single | double

Output

Y1 — Output signal

matrix

Port Y1 always corresponds to a lowpass filter.

Dependencies

Available if Number of crossovers is set to 1, 2, 3, or 4.

Data Types: single | double

Y2 — Output signal

matrix

Depending on the number of crossovers specified, port Y2 outputs the original audio signal passed through a bandpass or highpass filter.

Dependencies

Available if Number of crossovers is set to 1, 2, 3, or 4.

Data Types: single | double

Y3 — Output signal

matrix

Depending on the number of crossovers specified, port Y3 corresponds to a bandpass or highpass filter of the original audio signal.

Dependencies

Available if Number of crossovers is set to 2, 3, or 4.

Data Types: single | double

Y4 — Output signal

matrix

Dependencies

Available if Number of crossovers is set to 3 or 4.

Data Types: single | double

Y5 — Output signal

matrix

Dependencies

Available if Number of crossovers is set to 4.

Data Types: single | double

Parameters

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

Number of crossovers — Number of magnitude response band crossings

1 (default) | 2 | 3 | 4

If you specify multiple crossovers, the corresponding Crossover frequency (Hz) and Crossover order parameters populate in the dialog box automatically.

The number of bands output by the Crossover Filter block is one more than the Number of crossovers.

Number of Crossovers	Number of Bands in Output
1	Two
2	Three
3	Four
4	Five

Crossover frequency (Hz) — Intersections of magnitude response bands

100 (default) | real scalar in the range 20 to 20000

Crossover frequencies are the intersections of magnitude response bands of the individual two-band crossover filters used in the multiband crossover filter.

Tunable: Yes

Crossover order — Order of individual crossover filters

2 (default) | integer in the range [0, 8]

The crossover filter order relates to the crossover filter slope in dB/octave: $$slope=N\times 6,$$ where N is the crossover order.

Tunable: Yes

View filter response — Open plot of magnitude response of each filter band

button

The plot is updated automatically when parameters of the Crossover Filter block change.

Tunable: Yes

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).

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

Interpreted execution (default) | Code generation

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

• Code generation – Simulate the 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 comparable to Interpreted execution.

Tunable: No

Model Examples

Two-Band Crossover Filtering for a Stereo Speaker System

Divide a mono signal into a stereo signal with distinct frequency bands. To hear the full effect of this simulation, use a stereo speaker system, such as headphones.

Block Characteristics

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

Algorithms

The Crossover Filter block is implemented as a binary tree of crossover pairs with additional phase-compensating sections [1]. Odd-order crossovers are implemented with Butterworth filters, while even-order crossovers are implemented with cascaded Butterworth filters (Linkwitz-Riley filters).

Odd-Order Crossover Pair

Odd-order two-band (one crossover) filters are implemented as parallel complementary highpass and lowpass filters.

LP and HP are Butterworth filters of order N, implemented as direct-form II transposed second-order sections. The shared cutoff frequency used in their design corresponds to the crossover of the resulting bands.

Even-Order Crossover Pair

Even-order two-band (one crossover) filters are implemented as parallel complementary highpass and lowpass filters.

LP and HP are Butterworth filters of order N/2, where N is the order of the overall filter. The filters are implemented as direct-form II transposed second-order sections.

For overall filters of orders 2 and 6, X_HI is multiplied by –1 internally so that the branches of your crossover pair are in-phase.

Even-Order Three-Band Filter

Even-order three-band (two crossovers) filters are implemented as parallel complementary highpass and lowpass filters organized in a tree structure.

The phase-compensating section is equivalent to an allpass filter.

The design of four-band and five-band filters (three and four crossovers) are extensions of the pattern developed for even-order and odd-order crossovers and the tree structure specified for three-band (two crossover) filters.

References

[1] D’Appolito, Joseph A. "Active Realization of Multiway All-Pass Crossover Systems." Journal of Audio Engineering Society. Vol. 35, Issue 4, 1987, pp. 239–245.

Extended Capabilities

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