phonTools (version 0.2-2.0)

makeFIR: Create a Digital Filter

Description

Design a Finite Impulse Response (FIR) Filter.

Usage

makeFIR (frequency, dB, order = 200, signal = NULL, window = 'hann', 
         verify = FALSE, interpolation = 'linear')

Arguments

frequency

The frequencies at which the frequency response of the filter will be specified. The first frequency specified must be equal to 0. The final frequency specified is assumed to be equal to fs/2.

dB

The power (in decibels) of the filter at each specified frequency.

order

The order of the signal.

signal

If a signal is provided, it is filtered and returned.

window

The type of window to be applied to the filter impulse response. Uses the windowfunc() function included in this package.

verify

If TRUE, a series of plots are created to allow the user to verify that the filter is appropriate.

interpolation

Determines 'linear' or 'cubic' interpolation between the specified points. Uses the interpolate() function included in this package.

Value

• If output = TRUE, the impulse response of the filter specified by the user is returned.

Details

Designs Type I FIR filters of odd length (even order). If an odd order is provided, 1 is added to the order. Filters are designed using the window-design method. The filter frequency response is defined at evenly-spaced locations determined by the filter order and the sampling frequency. If frequency specifications do not fall exactly on these points, the nearest appropriate location is used. This design method may lead to 'undesirable' behaviour between specified frequencies. This can be minimized by increasing the filter order and selecting an appropriate window function.

References

Lyons, R. G. (2004). Understanding Digital Signal Processing (2nd ed.). Prentice Hall.

Examples

## specify a filter with an arbitrary response
frequency = c(0, 500, 502, 5000, 5002, 7000, 7002, 11025)
dB = c(0, 0, -50,  -50, -10,  -10, -70, -70)

## create the filter and verify that the frequency response is as desired
testfilter = makeFIR (frequency, dB, verify = TRUE, order = 1500)
spectralslice (testfilter, padding = 1000)


## create the filter and verify that the frequency response is as desired
makeFIR (frequency, dB, verify = TRUE, order = 300, signal = rnorm (1400))