Digital Filtering in Matlab

Digital filtering is a widely used technique that is common in many fields of science and engineering.  Filters remove unwanted signals and noise from a desired signal.  There are many different kinds of filters, including low pass, high pass, band pass and band stop filters.  There is a large collection of filters that famous engineers and mathematicians have invented, including Hanning, Hamming, Blackman, Kaiser and Tukey windows.


y = filter(b,a,x) filters the input data, x, using a rational transfer function defined by the numerator and denominator coefficients b and a, respectively.
If a(1) is not equal to 1, then filter normalizes the filter coefficients by a(1). Therefore, a(1) must be nonzero.

y - Filtered data, returned as a vector, matrix, or multidimensional array of the same size as the input data, x.

• If x is a vector, then filter returns the filtered data as a vector of the same size as x.
• If x is a matrix, then filter acts along the first dimension and returns the filtered data for each column.
• If x is a multidimensional array, then filter acts along the first array dimension whose size does not equal 1. 

* 'low' : Low-pass filters, which remove frequencies greater than some specified value.
* 'high' : High-pass filters, which remove frequencies lower than some specified value.
* 'stop' : Stop-band filters, which remove frequencies in a given range of values.