Package: dsp
Reconstruct signals from subbands
The DyadicSynthesisFilterBank
object reconstructs
signals from subbands with smaller bandwidths and lower sample rates.
The filter bank uses a series of highpass and lowpass FIR filters
to repeatedly reconstruct the signal.
To reconstruct signals from subbands with smaller bandwidths and lower sample rates:
Define and set up your synthesis filter bank. See Construction.
Call step
to reconstruct
the signal according to the properties of dsp.DyadicSynthesisFilterBank
.
The behavior of step
is specific to each object in
the toolbox.
H = dsp.DyadicSynthesisFilterBank
returns
a synthesis filter bank, H
, that reconstructs a
signal from its subbands with smaller bandwidths and smaller sample
rates.
H = dsp.DyadicSynthesisFilterBank('
returns
a synthesis filter bank, Propertyname
',PropertyValue
,...)H
, with each specified
property set to the specified value.

Type of filter used in filter bank Specify the type of filter used to determine the highpass and
lowpass FIR filters in the filter bank as one of
In order to automatically design waveletbased filters, install
the Wavelet Toolbox product. Otherwise, use the  

Lowpass FIR filter coefficients Specify a vector of lowpass FIR filter coefficients, in descending
powers of z. Use a halfband filter that passes
the frequency band stopped by the filter specified in the  

Highpass FIR filter coefficients Specify a vector of highpass FIR filter coefficients, in descending
powers of z. Use a halfband filter that passes
the frequency band stopped by the filter specified in the  

Wavelet order Specify the order of the wavelet selected in the  

Wavelet order for synthesis filter stage Specify the order of the wavelet for the synthesis filter stage as:
This property applies only when you set the  

Number of filter bank levels Specify the number of filter bank levels as a scalar integer.
An Nlevel asymmetric structure has N + 1 input subbands, and an Nlevel
symmetric structure has 2^{N} input
subbands. The default is rg  

Structure of filter bank Specify the structure of the filter bank as 
clone  Create synthesis filter bank object with same property values 
getNumInputs  Number of expected inputs to step method 
getNumOutputs  Number of outputs of the step method 
isLocked  Locked status for input attributes and nontunable properties 
release  Allow property value and input characteristics changes 
step  Reconstruct signal from high and lowfrequency subbands 
Remove noise from a signal using filter banks:
t = 0:.0001:.0511; x= square(2*pi*30*t); xn = x' + 0.08*randn(length(x),1); hdydanl = dsp.DyadicAnalysisFilterBank; % The filter coefficients correspond to a 'haar' wavelet. hdydanl.CustomLowpassFilter = [1/sqrt(2) 1/sqrt(2)]; hdydanl.CustomHighpassFilter = [1/sqrt(2) 1/sqrt(2)]; hdydsyn = dsp.DyadicSynthesisFilterBank; hdydsyn.CustomLowpassFilter = [1/sqrt(2) 1/sqrt(2)]; hdydsyn.CustomHighpassFilter = [1/sqrt(2) 1/sqrt(2)]; C = step(hdydanl, xn); % Subband outputs C1 = C(1:256); C2 = C(257:384); C3 = C(385:512); % Set highfrequency coefficients to zero to remove noise. x_den = step(hdydsyn, ... [zeros(length(C1),1); ... zeros(length(C2),1); ... C3]); subplot(2,1,1), plot(xn); title('Original Noisy Signal'); subplot(2,1,2), plot(x_den); title('Denoised Signal');
This object implements the algorithm, inputs, and outputs described on the Dyadic Synthesis Filter Bank block reference page. The object properties correspond to the block parameters, except:
The object only receives data as a vector or matrix of concatenated
subbands, as specified using the step method. 