Two-Channel Synthesis Subband Filter

Reconstruct signal from high-frequency and low-frequency subbands

Libraries:
DSP System Toolbox / Filtering / Multirate Filters

Description

The Two-Channel Synthesis Subband Filter block reconstructs a signal from its high-frequency and low-frequency subbands, each with half the bandwidth and half the sample rate of the original signal. Use this block to reconstruct signals decomposed by the Two-Channel Analysis Subband Filter block.

The block upsamples the high- and low-frequency subbands by 2, and then filters the results with a pair of highpass and lowpass FIR filters, as shown in this figure.

The block implements the FIR filtering and downsampling steps together using a polyphase filter structure, which is more efficient than the interpolate-then-filter algorithm shown in the preceding figure. You can implement a multilevel dyadic synthesis filter bank by connecting multiple copies of this block or by using the Dyadic Synthesis Filter Bank block. For more information, see Creating Multilevel Dyadic Synthesis Filter Banks.

You must provide a vector of filter coefficients for the lowpass and highpass FIR filters. Each filter should be a half-band filter that passes the frequency band that the other filter stops. You can use this block to reconstruct the output of a Two-Channel Analysis Subband Filter block. To do so, you must design the filters in this block such that they perfectly reconstruct the outputs of the analysis filters.

Ports

Input

expand all

Specify the high-frequency subband as a vector or a matrix. Both the high-frequency subband and the low-frequency subbands must have the same size and data type.

When the input is fixed-point, it must be signed only.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `fixed point`
Complex Number Support: Yes

Specify the low-frequency subband as a vector or a matrix. Both the high-frequency subband and the low-frequency subbands must have the same size and data type.

When the input is fixed-point, it must be signed only.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `fixed point`
Complex Number Support: Yes

Output

expand all

The block returns the synthesized output as a vector or a matrix. The number of rows in the output is the sum of the number of rows of the input signals.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `fixed point`
Complex Number Support: Yes

Parameters

expand all

Main Tab

A vector of lowpass FIR filter coefficients, in descending powers of z. The lowpass filter should be a half-band filter that passes the frequency band stopped by the filter specified in the Highpass FIR filter coefficients parameter. To use this block to reconstruct the output of a Two-Channel Analysis Subband Filter block, you must design the filters in this block to perfectly reconstruct the outputs of the analysis filters. For more information, see Specify FIR Filters.

A vector of highpass FIR filter coefficients, in descending powers of z. The highpass filter should be a half-band filter that passes the frequency band stopped by the filter specified in the Lowpass FIR filter coefficients parameter. To use this block to reconstruct the output of a Two-Channel Analysis Subband Filter block, you must design the filters in this block to perfectly reconstruct the outputs of the analysis filters. For more information, see Specify FIR Filters.

Specify how the block should process the input. You can set this parameter to one of the following options:

• `Columns as channels (frame based)` (default) — When you select this option, the block treats each column of the input as a separate channel.

• `Elements as channels (sample based)` — When you select this option, the block treats each element of the input as a separate channel.

Specify the rate processing rule for the block. You can set this parameter to one of the following options:

• `Enforce single-rate processing` — When you select this option, the block treats each column of the input as an independent channel and reconstructs each channel over time. The output has the same sample rate as the input, but the output frame size is twice that of the input frame size. To select this option, you must set the Input processing parameter to ```Columns as channels (frame based)```.

• `Allow multirate processing` — When you select this option, the input and output of the block are the same size, but the sample rate of the output is twice that of the input.

Some settings of this parameter cause the block to have nonzero latency. See Latency for more information.

Data Types Tab

Select the rounding mode for fixed-point operations. The filter coefficients do not obey this parameter; they always round to `Nearest`.

Note

The Rounding mode and Saturate on integer overflow settings have no effect on numerical results when all the following conditions exist:

• Product output is ```Inherit: Inherit via internal rule```

• Accumulator is ```Inherit: Inherit via internal rule```

• Output is ```Inherit: Same as accumulator```

With these data type settings, the block effectively operates in full-precision mode.

When you select this parameter, the block saturates the result of its fixed-point operation. When you clear this parameter, the block wraps the result of its fixed-point operation. For details on `saturate` and `wrap`, see overflow mode for fixed-point operations.

Note

The Rounding mode and Saturate on integer overflow parameters have no effect on numeric results when all these conditions are met:

• Product output data type is ```Inherit: Inherit via internal rule```.

• Accumulator data type is ```Inherit: Inherit via internal rule```.

With these data type settings, the block operates in full-precision mode.

Specify the coefficients data type. See Fixed-Point Data Types and Multiplication Data Types for illustrations depicting the use of the coefficients data type in this block. You can set it to:

• A rule that inherits a data type, for example, ```Inherit: Same word length as input```

• An expression that evaluates to a valid data type, for example, `fixdt(1,16,0)`

Click the button to display the Data Type Assistant, which helps you set the Coefficients parameter.

Specify the minimum value of the filter coefficients. The default value is `[]` (unspecified). Simulink® software uses this value to perform automatic scaling of fixed-point data types.

Specify the maximum value of the filter coefficients. The default value is `[]` (unspecified). Simulink software uses this value to perform automatic scaling of fixed-point data types.

Specify the product output data type. See Fixed-Point Data Types and Multiplication Data Types for illustrations depicting the use of the product output data type in this block. You can set it to:

• A rule that inherits a data type, for example, ```Inherit: Inherit via internal rule```. For more information on this rule, see Inherit via Internal Rule.

Note

The actual product output word length can be equal to or greater than the calculated ideal product output word length, depending on the settings on the Hardware Implementation pane of the Configuration Parameters dialog box.

• An expression that evaluates to a valid data type, for example, `fixdt(1,16,0)`

Click the button to display the Data Type Assistant, which helps you set the Product output parameter.

Specify the accumulator data type. See Fixed-Point Data Types for illustrations depicting the use of the accumulator data type in this block. You can set this parameter to:

• A rule that inherits a data type, for example, ```Inherit: Inherit via internal rule```. For more information on this rule, see Inherit via Internal Rule.

• An expression that evaluates to a valid data type, for example, `fixdt(1,16,0)`

Click the button to display the Data Type Assistant, which helps you set the Accumulator parameter.

Specify the output data type. See Fixed-Point Data Types for illustrations depicting the use of the output data type in this block. You can set it to:

• A rule that inherits a data type, for example, ```Inherit: Same as accumulator```

• An expression that evaluates to a valid data type, for example, `fixdt(1,16,0)`

Click the button to display the Data Type Assistant, which helps you set the Output parameter.

Specify the minimum value that the block should output. The default value is `[]` (unspecified). Simulink software uses this value to perform:

• Simulation range checking (see Specify Signal Ranges (Simulink))

• Automatic scaling of fixed-point data types

Specify the maximum value that the block should output. The default value is `[]` (unspecified). Simulink software uses this value to perform:

• Simulation range checking (see Specify Signal Ranges (Simulink))

• Automatic scaling of fixed-point data types

Select this parameter to prevent the fixed-point tools from overriding the data types you specify in the block dialog box.

Block Characteristics

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

expand all

References

[1] Fliege, N. J. Multirate Digital Signal Processing: Multirate Systems, Filter Banks, Wavelets . West Sussex, England: John Wiley & Sons, 1994.

[2] Strang, G. and T. Nguyen. Wavelets and Filter Banks . Wellesley, MA: Wellesley-Cambridge Press, 1996.

[3] Vaidyanathan, P. P. Multirate Systems and Filter Banks . Englewood Cliffs, NJ: Prentice Hall, 1993.

Version History

Introduced before R2006a