Signal Processing Blockset™

Vector Quantizer Decoder

Find vector quantizer codeword that corresponds to given, zero-based index value

Library

Quantizers

dspquant2

Description

The Vector Quantizer Decoder block associates each input index value with a codeword, a column vector of quantized output values defined in the Codebook values parameter. When you input multiple index values into this block, the block outputs a matrix of quantized output vectors. This matrix is created by horizontally concatenating the codeword vectors that correspond to each index value.

You can select how you want to enter the codebook values using the Source of codebook parameter. When you select Specify via dialog, you can type the codebook values into the block parameters dialog box. Select Input port and port C appears on the block. The block uses the input to port C as the Codebook values parameter.

The Codebook values parameter is a k-by-N matrix of values, where k ≥ 1 and N ≥ 1. Each column of this matrix is a codeword vector, and each codeword vector corresponds to an index value. The index values are zero based; therefore, the first codeword vector corresponds to an index value of 0, the second codeword vector corresponds to an index value of 1, and so on.

The input to this block is a vector of index values, where 0 ≤ index < N and N is the number of columns of the codebook matrix. Use the Action for out of range index value parameter to determine how the block behaves when an input index value is out of this range. When you want any index values less than 0 to be set to 0 and any index values greater than or equal to N to be set to N-1, select Clip. When you want to be warned when any index values less than 0 are set to 0 and any index values greater than or equal to N are set to N-1, select Clip and warn. When you want the simulation to stop and display an error when the index values are out of range, select Error.

Data Type Support

The input to the block can be the index values and the codebook values. The data type of the index input to the block at port I can be uint8, uint16, uint32, int8, int16, or int32. The data type of the codebook values can be double, single, or Fixed-point.

The output of the block is the quantized output values. These quantized output values always have the same data type as the codebook values. When the codebook values are specified via an input port, the block assigns the same data type to the Q(U) output port. When the codebook values are specified via the dialog, use the Codebook and output data type parameter to specify the data type of the Q(U) output port. The data type of the codebook and quantized output can be Same as input, double, single, Fixed-point, User-defined, or Inherit via back propagation.

Dialog Box

Source of codebook

Choose Specify via dialog to type the codebook values into the block parameters dialog box. Select Input port to specify the codebook values using the block's input port, C.

Action for out of range index value

Choose the behavior of the block when an input index value is out of range, where 0 ≤ index < N and N is the length of the codebook vector. Select Clip when you want any index values less than 0 to be set to 0 and any index values greater than or equal to N to be set to N-1. Select Clip and warn when you want to be warned when any index values less than 0 are set to 0 and any index values greater than or equal to N are set to N-1. Select Error when you want the simulation to stop and display an error when the index values are out of range.

Codebook values

Enter a k-by-N matrix of quantized output values, where 1 ≤ k and 1 ≤ N . Each column of your matrix corresponds to an index value. This parameter is visible if, from the Source of codebook list, you select Specify via dialog.

Codebook and output data type

Use this parameter to specify the data type of the codebook and quantized output values. The data type can be Same as input, double, single, Fixed-point, User-defined, orInherit via back propagation. This parameter becomes visible when you select Specify via dialog for the Source of codebook parameter.

Signed

Select to output a signed fixed-point signal. Otherwise, the signal is unsigned. This parameter is only visible if, from the Codebook and output data type list, you select Fixed-point.

Word length

Specify the word length, in bits, of the fixed-point output data type. This parameter is only visible if, from the Codebook and output data type list, you select Fixed-point.

Set fraction length in output to

Specify the scaling of the fixed-point output by either of the following two methods:

• Choose Best precision to have the output scaling automatically set such that the output signal has the best possible precision.

• Choose User-defined to specify the output scaling in the Fraction length parameter.

This parameter is only visible if, from the Codebook and output data type list, you select Fixed-point or when you select User-defined and the specified output data type is a fixed-point data type.

Fraction length

For fixed-point output data types, specify the number of fractional bits, or bits to the right of the binary point. This parameter is only visible when you select Fixed-point or User-defined for the Codebook and output data type parameter and User-defined for the Set fraction length in output to parameter.

User-defined data type

Specify any built-in or fixed-point data type. You can specify fixed-point data types using the following Simulink Fixed Point functions: sfix, ufix, sint, uint, sfrac, and ufrac. This parameter is only visible when you select User-defined for the Codebook and output data type parameter.

References

Gersho, A. and R. Gray. Vector Quantization and Signal Compression. Boston: Kluwer Academic Publishers, 1992.

Supported Data Types

See Also

Variance

Vector Quantizer Design