resample: Resample a vector

In soundgen: Sound Synthesis and Acoustic Analysis

Resample a vector

Description

Changes the sampling rate without introducing artefacts like aliasing. Best for relatively short vectors that require special care (eg pitch contours that contain NAs, which need to be dropped or preserved) as the algorithm is too slow for long sounds. Algorithm: to downsample, applies a low-pass filter, then decimates with approx; to upsample, performs linear interpolation with approx, then applies a low-pass filter. NAs can be interpolated or preserved in the output. The length of output is determined, in order of precedence, by len / mult / samplingRate_new. For simple vector operations, this is very similar to approx, but the leading and trailing NAs are also preserved (see examples).

Usage

resample(
  x,
  samplingRate = NULL,
  samplingRate_new = NULL,
  mult = NULL,
  len = NULL,
  lowPass = TRUE,
  na.rm = FALSE,
  reportEvery = NULL,
  cores = 1,
  saveAudio = NULL,
  plot = FALSE,
  savePlots = NULL,
  width = 900,
  height = 500,
  units = "px",
  res = NA,
  ...
)

Arguments

x	path to a folder, one or more wav or mp3 files c('file1.wav', 'file2.mp3'), Wave object, numeric vector, or a list of Wave objects or numeric vectors
samplingRate	sampling rate of x (only needed if x is a numeric vector)
samplingRate_new	an alternative to mult provided that the old samplingRate is know (NB: mult takes precedence)
mult	multiplier of sampling rate: new sampling rate = old sampling rate x mult, so 1 = no effect, >1 = upsample, <1 = downsample
len	if specified, overrides mult and samplingRate_new and simply returns a vector of length len
lowPass	if TRUE, applies a low-pass filter before decimating or after upsampling to avoid aliasing
na.rm	if TRUE, NAs are interpolated, otherwise they are preserved in the output
reportEvery	when processing multiple inputs, report estimated time left every ... iterations (NULL = default, NA = don't report)
cores	number of cores for parallel processing
saveAudio	full path to the folder in which to save audio files (one per detected syllable)
plot	should a spectrogram be plotted? TRUE / FALSE
savePlots	full path to the folder in which to save the plots (NULL = don't save, ” = same folder as audio)
width, height, units, res	graphical parameters for saving plots passed to png
...	other graphical parameters

Examples

## Example 1: a short vector with NAs
x = c(NA, 1, 2, 3, NA, NA, 6, 7, 8, NA)

# upsample
resample(x, mult = 3.5, lowPass = FALSE, plot = TRUE)  # just approx
resample(x, mult = 3.5, lowPass = TRUE, plot = TRUE) # low-pass + approx
resample(x, mult = 3.5, lowPass = FALSE, na.rm = TRUE, plot = TRUE)

# downsample
resample(x, mult = 0.5, lowPass = TRUE, plot = TRUE)
resample(x, mult = 0.5, na.rm = TRUE, plot = TRUE)
resample(x, len = 5, na.rm = TRUE, plot = TRUE) # same

# The most important TIP: use resample() for audio files and the internal
# soundgen:::.resample(list(sound = ...)) for simple vector operations because
# it's >1000 times faster. For example:
soundgen:::.resample(list(sound = x), mult = 3.5, lowPass = FALSE)

## Example 2: a sound
silence = rep(0, 10)
samplingRate = 1000
fr = seq(100, 300, length.out = 400)
x = c(silence, sin(cumsum(fr) * 2 * pi / samplingRate), silence)
spectrogram(x, samplingRate)

# downsample
x1 = resample(x, mult = 1 / 2.5)
spectrogram(x1, samplingRate / 2.5)  # no aliasing
# cf:
x1bad = resample(x, mult = 1 / 2.5, lowPass = FALSE)
spectrogram(x1bad, samplingRate / 2.5)  # aliasing

# upsample
x2 = resample(x, mult = 3)
spectrogram(x2, samplingRate * 3)  # nothing above the old Nyquist
# cf:
x2bad = resample(x, mult = 3, lowPass = FALSE)
spectrogram(x2bad, samplingRate * 3)  # high-frequency artefacts

## Not run: 
# Example 3: resample all audio files in a folder to 8000 Hz
resample('~/Downloads/temp', saveAudio = '~/Downloads/temp/sr8000/',
         samplingRate_new = 8000, savePlots = '~/Downloads/temp/sr8000/')

## End(Not run)

soundgen documentation built on April 4, 2025, 3:44 a.m.