g=blfilter(winname,fsupp,fc); g=blfilter(winname,fsupp,fc,...);
| winname | Name of prototype |
| fsupp | Support length of the prototype |
blfilter(winname,fsupp) constructs a band-limited filter. The parameter winname specifies the shape of the frequency response. The name must be one of the shapes accepted by firwin. The support of the frequency response measured in normalized frequencies is specified by fsupp.
blfilter(winname,fsupp,fc) constructs a filter with a centre frequency of fc measured in normalized frequencies.
If one of the inputs is a vector, the output will be a cell array with one entry in the cell array for each element in the vector. If more input are vectors, they must have the same size and shape and the filters will be generated by stepping through the vectors. This is a quick way to create filters for filterbank and ufilterbank.
blfilter accepts the following optional parameters:
| 'fs',fs | If the sampling frequency fs is specified then the support fsupp and the centre frequency fc is specified in Hz. |
| 'complex' | Make the filter complex valued if the centre frequency is non-zero. This is the default. |
| 'real' | Make the filter real-valued if the centre frequency is non-zero. |
| 'delay',d | Set the delay of the filter. Default value is zero. |
| 'scal',s | Scale the filter by the constant s. This can be useful to equalize channels in a filter bank. |
| 'pedantic' | Force window frequency offset (g.foff) to a subsample precision by a subsample shift of the firwin output. |
It is possible to normalize the transfer function of the filter by passing any of the flags from the setnorm function. The default normalization is 'energy'.
The filter can be used in the pfilt routine to filter a signal, or in can be placed in a cell-array for use with filterbank or ufilterbank.
The output g from blfilter is a structure. This type of structure can be used to describe any bandlimited filter defined in terms of its transfer function. The structure contains the following fields:
| g.H | This is an anonymous function taking the transform length L as input and producing the bandlimited transfer function in the form of a vector. |
| g.foff | This is an anonymous function taking the transform length L as input and procing the frequency offset of H as an integer. The offset is the value of the lowest frequency of H measured in frequency samples. foff is used to position the bandlimited tranfer function stored in H correctly when multiplying in the frequency domain. |
| g.delay | This is the desired delay of the filter measured in samples. |
| g.realonly | This is an integer with value 1 if the filter defined a real-valued filter. In this case, the bandlimited transfer function H will be mirrored from the positive frequencies to the negative frequencies. If the filter is a natural lowpass filter correctly centered around 0, realonly does not need to be 1. |
| g.fs | The intended sampling frequency. This is an optional parameter that is only used for plotting and visualization. |