phonTools (version 0.1-5)

makeFIR: Create a Digital Filter

Description

Design a Finite Impulse Response (FIR) Filter.

Usage

makeFIR (frequency, power, output = TRUE, verify = FALSE)

Arguments

frequency

The frequencies at which the frequency response of the filter will be specified. These points must be specified only at multiples of 2.5 Hz. The first point in this vector must equal 0, and the last point is assumed to be equal to fs/2 (the Nyquist freque

power

The power (in decibels) of the filter at each specified frequency. The power range may not exceed 96 dB.

output

If TRUE, the filtered vector is returned.

verify

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

Value

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

Details

This function allows the user to create a FIR filter (specified by an impulse response) with an arbitrary frequency response using the frequency sampling method. If verify is TRUE, a figure is created which allows the user to inspect the performance of the function. The panels correspond to the following information: Left: The frequency response of the filter. This should resemble the frequency response specified by the user. Right: The phase response of the filter. This should be linear, save for a jump when at the top and bottom y-axis ranges of the figure.

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, 502.5, 5000, 5002.5, 7000, 7002.5, 11025)
power =     c(0, 0,     -50,  -50,    -10,  -10,    -70,   -70)

## create the filter and verify that the frequency response is as desired
testfilter = makeFIR (frequency, power, verify = TRUE)

## create a vector of random noise
noise = rnorm (2000, 0, 200)

## filter the sound using the verify parameter in order to 
## verify that the filtered sound has the desired spectral envelope
snd = FIRfilter (noise, testfilter, verify = TRUE)