Design a digital filter

Provides 'FIR' and 'IIR' filter options; default is 'FIR', see also design_filter_fir; for 'IIR' filters, see design_filter_iir.

Usage

design_filter(
  sample_rate,
  data = NULL,
  method = c("fir_kaiser", "firls", "fir_remez", "butter", "cheby1", "cheby2", "ellip"),
  high_pass_freq = NA,
  high_pass_trans_freq = NA,
  low_pass_freq = NA,
  low_pass_trans_freq = NA,
  passband_ripple = 0.1,
  stopband_attenuation = 40,
  filter_order = NA,
  ...,
  data_size = length(data)
)

Arguments

sample_rate

data sample rate

data

data to be filtered, can be optional (NULL)

method

filter method, options are "fir" (default), "butter", "cheby1", "cheby2", and "ellip"

high_pass_freq, low_pass_freq

high-pass or low-pass frequency, see design_filter_fir or design_filter_iir

high_pass_trans_freq, low_pass_trans_freq

transition bandwidths, see design_filter_fir or design_filter_iir

passband_ripple

allowable pass-band ripple in decibel; default is 0.1

stopband_attenuation

minimum stop-band attenuation (in decibel) at transition frequency; default is 40 dB.

filter_order

suggested filter order; 'RAVE' may or may not adopt this suggestion depending on the data and numerical feasibility

...

passed to filter generator functions

data_size

used by 'FIR' filter design to determine maximum order, ignored in 'IIR' filters; automatically derived from data

Value

If data is specified and non-empty, this function returns filtered data via forward and backward filtfilt; if data is NULL, then returns the generator function.

Examples

sample_rate <- 200
t <- seq(0, 10, by = 1 / sample_rate)
x <- sin(t * 4 * pi) + sin(t * 20 * pi) +
  2 * sin(t * 120 * pi) + rnorm(length(t), sd = 0.4)

# ---- Using FIR ------------------------------------------------

# Low-pass filter
y1 <- design_filter(
  data = x,
  sample_rate = sample_rate,
  low_pass_freq = 3, low_pass_trans_freq = 0.5
)

# Band-pass cheby1 filter 8-12 Hz with custom transition
y2 <- design_filter(
  data = x,
  method = "cheby1",
  sample_rate = sample_rate,
  low_pass_freq = 12, low_pass_trans_freq = .25,
  high_pass_freq = 8, high_pass_trans_freq = .25
)

y3 <- design_filter(
  data = x,
  sample_rate = sample_rate,
  low_pass_freq = 80,
  high_pass_freq = 30
)

oldpar <- par(mfrow = c(2, 1),
              mar = c(3.1, 2.1, 3.1, 0.1))
plot(t, x, type = 'l', xlab = "Time", ylab = "",
     main = "Mixture of 2, 10, and 60Hz", xlim = c(0,1))
# lines(t, y, col = 'red')
lines(t, y3, col = 'green')
lines(t, y2, col = 'blue')
lines(t, y1, col = 'red')
legend(
  "topleft", c("Input", "Low: 3Hz", "Pass 8-12Hz", "Pass 30-80Hz"),
  col = c(par("fg"), "red", "blue", "green"), lty = 1,
  cex = 0.6
)

# plot pwelch
pwelch(x, fs = sample_rate, window = sample_rate * 2,
       noverlap = sample_rate, plot = 1, ylim = c(-100, 10))
pwelch(y1, fs = sample_rate, window = sample_rate * 2,
       noverlap = sample_rate, plot = 2, col = "red")
pwelch(y2, fs = sample_rate, window = sample_rate * 2,
       noverlap = sample_rate, plot = 2, col = "blue")
pwelch(y3, fs = sample_rate, window = sample_rate * 2,
       noverlap = sample_rate, plot = 2, col = "green")



# ---- Clean this demo --------------------------------------------------
par(oldpar)