compand

Source code mu-law or A-law compressor or expander

Syntax

`out = compand(in,param,v) out = compand(in,Mu,v,'mu/compressor') out = compand(in,Mu,v,'mu/expander') out = compand(in,A,v,'A/compressor') out = compand(in,A,v,'A/expander') `

Description

`out = compand(in,param,v) ` implements a µ-law compressor for the input vector `in`. `Mu` specifies µ, and `v` is the input signal's maximum magnitude. `out` has the same dimensions and maximum magnitude as `in`.

`out = compand(in,Mu,v,'mu/compressor') ` is the same as the syntax above.

`out = compand(in,Mu,v,'mu/expander') ` implements a µ-law expander for the input vector `in`. `Mu` specifies µ and `v` is the input signal's maximum magnitude. `out` has the same dimensions and maximum magnitude as `in`.

`out = compand(in,A,v,'A/compressor') ` implements an A-law compressor for the input vector `in`. The scalar `A` is the A-law parameter, and `v` is the input signal's maximum magnitude. `out` is a vector of the same length and maximum magnitude as `in`.

`out = compand(in,A,v,'A/expander') ` implements an A-law expander for the input vector `in`. The scalar `A` is the A-law parameter, and `v` is the input signal's maximum magnitude. `out` is a vector of the same length and maximum magnitude as `in`.

 Note:   The prevailing parameters used in practice are µ= 255 and A = 87.6.

Examples

The examples below illustrate the fact that compressors and expanders perform inverse operations.

```compressed = compand(1:5,87.6,5,'a/compressor') expanded = compand(compressed,87.6,5,'a/expander')```

The output is

```compressed = 3.5296 4.1629 4.5333 4.7961 5.0000 expanded = 1.0000 2.0000 3.0000 4.0000 5.0000 ```

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Algorithms

For a given signal x, the output of the µ-law compressor is

$y=\frac{V\mathrm{log}\left(1+\mu |x|/V\right)}{\mathrm{log}\left(1+\mu \right)}\mathrm{sgn}\left(x\right)$

where V is the maximum value of the signal x, µ is the µ-law parameter of the compander, log is the natural logarithm, and sgn is the signum function (`sign` in MATLAB).

The output of the A-law compressor is

where A is the A-law parameter of the compander and the other elements are as in the µ-law case.

References

[1] Sklar, Bernard, Digital Communications: Fundamentals and Applications, Englewood Cliffs, NJ, Prentice-Hall, 1988.