Apply gamma-tone filters to obtain auditory envelopes

Usage

gammatone_fast(
  x,
  sample_rate,
  center_frequencies,
  n_bands,
  use_hilbert = TRUE,
  downsample = NA,
  downsample_before_hilbert = FALSE
)

Arguments

x: a numeric vector or matrix; if x is a matrix, it should be column-major (each column is a sound track)
sample_rate: sampling frequency
center_frequencies: center frequencies at which the envelopes will be derived; can be either a length of two defining the lower and upper bound, and using n_bands to interpolate automatically, or a length of multiple, with the frequencies specified explicitly
n_bands: number of the center frequencies, can be missing if center_frequencies is explicit and no interpolation is needed; if specified, then the frequencies will be interpolated using equivalent rectangular bandwidth rate ('ERB')
use_hilbert: whether to apply 'Hilbert' transform; default is true, which calculates the magnitude; set to false when only the filter is needed
downsample: whether to down-sample the envelopes after the filters; default is NA (no down-sample).
downsample_before_hilbert: whether the down-sample happens before or after the 'Hilbert' transform so speed up the computation if the signal is too long; only used when downsample is greater than 1; default is FALSE. Use with caution, especially when the voice center frequency is close to the 'Nyquist' frequency. However, if used properly, there will be significant performance boost on large signals with high sampling rates

Value

A file-array object of filtered and potentially down-sampled data; see 'Examples' on how to use this function.

Examples



fs <- 4000
time <- seq_len(8000) / fs
x <- sin(160 * pi * time) +
  sin(1000 * pi * time) * dnorm(time, mean = 1, sd = 0.1) +
  0.5 * rnorm(length(time))

# envelope
result <- gammatone_fast(
  x,
  sample_rate = fs,
  center_frequencies = c(20, 1000),
  n_bands = 128,

  # default downsample happens after hilbert
  downsample = 40
)


oldpar <- par(mfrow = c(2, 1))

plot(
  time,
  x,
  type = "l",
  xlab = "Time",
  ylab = "",
  main = "Original mixed 80Hz and 500Hz"
)

# only one channel
envelope <- subset(result, Channel ~ Channel == 1, drop = TRUE)
dnames <-  dimnames(envelope)
image(
  x = as.numeric(dnames$Time),
  y = as.numeric(dnames$Frequency),
  z = envelope,
  xlab = "Time",
  ylab = "Frequency",
  main = "Envelope from 20Hz to 1000Hz"
)




par(oldpar) # reset graphics state