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Compand a Signal

In certain applications, such as speech processing, it is common to use a logarithm computation, called a compressor, before quantizing a signal. The inverse operation of a compressor is called an expander. The combination of a compressor and expander is called a compander. You can use the compand function to implement a compander.

Compress and Expand Data Sequence Using Mu-Law

Open Live Script

This example implements a compander by using a mu-law compressor and expander.

Generate a data sequence.

data = 2:2:12
data = 1×6

     2     4     6     8    10    12

Compress the data sequence by using a mu-law compressor. Set the value for mu to 255. The compressed data sequence now ranges between 8.1 and 12.

compressed = compand(data,255,max(data),'mu/compressor')
compressed = 1×6

    8.1644    9.6394   10.5084   11.1268   11.6071   12.0000

Expand the compressed data sequence by using a mu-law expander. The expanded data sequence is nearly identical to the original data sequence.

expanded = compand(compressed,255,max(data),'mu/expander')
expanded = 1×6

    2.0000    4.0000    6.0000    8.0000   10.0000   12.0000

Calculate the difference between the original data sequence and the expanded sequence.

diffvalue = expanded - data
diffvalue = 1×6
10-14 ×

   -0.0444    0.1776    0.0888    0.1776    0.1776   -0.3553

Compress and Expand Data Sequence Using A-Law

Open Live Script

This example implements a compander by using an A-law compressor and expander.

Generate a data sequence.

data = 1:5;

Compress the data sequence by using an A-law compressor. Set the value for A to 87.6. The compressed data sequence now ranges between 3.5 and 5.

compressed = compand(data,87.6,max(data),'A/compressor')
compressed = 1×5

    3.5296    4.1629    4.5333    4.7961    5.0000

Expand the compressed data sequence by using an A-law expander. The expanded data sequence is nearly identical to the original data sequence.

expanded = compand(compressed,87.6,max(data),'A/expander')
expanded = 1×5

    1.0000    2.0000    3.0000    4.0000    5.0000

Calculate the difference between the original data sequence and the expanded sequence.

diffvalue = expanded - data
diffvalue = 1×5
10-14 ×

         0         0    0.1332    0.0888    0.0888

See Also

Functions

Related Topics