resample: Resample a vector

In soundgen: Sound Synthesis and Acoustic Analysis

Resample a vector

Description

Changes the sampling rate of a sound or another time series without aliasing. Similar in spirit and speed to resample in the signal package, but also works for short vectors and preserves NAs approximately after resampling. Use resample() for interpolation when the points are evenly spaced, when there are missing values, or when we care about aliasing. When the points are unevenly spaced, use interpolate instead, but then there should not be any missing values.

Usage

resample(
  x,
  samplingRate = NULL,
  samplingRate_new = NULL,
  mult = NULL,
  len = NULL,
  lowPass = TRUE,
  interpol = "splineFC",
  na.rm = FALSE,
  reportEvery = NULL,
  cores = 1,
  saveAudio = FALSE,
  plot = FALSE,
  savePlots = FALSE,
  embed = FALSE,
  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 known (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
interpol	the method of interpolation (only used for upsampling, not downsampling); see interpolate for details
na.rm	if TRUE, NAs are linearly interpolated before resampling; if FALSE they are preserved in the interpolated output in (approximately) the same position
reportEvery	when processing multiple inputs, report estimated time left every reportEvery iterations (NULL = default, NA = don't report); see reportTime
cores	number of cores for parallel processing
saveAudio	if TRUE, saves the processed audio in a subdirectory named after the function and created in the input directory (if input is a file or folder) or in the working directory
plot	if TRUE, produces a plot of the results
savePlots	if TRUE, creates a subdirectory in the input directory (if input is a file or folder) or in the working directory (if input is a vector etc), named after the function (eg "spectrogram/"). All plots and audio files (if any) are saved in this new directory. If there are multiple inputs, an html notebook is also created for easy viewing and listening
embed	if TRUE and savePlots is set and there are multiple inputs, all saved images and audio (if any) are embedded in the exported html notebook for easy sharing; if FALSE, the html file links to separate images and audio files (but separate files are still saved). NB: for this to work, package "base64enc" must be installed
width, height, units, res	graphical parameters for saving plots passed to png

Details

Algorithm: to downsample, applies a low-pass filter, then decimates with spline; to upsample, performs a specified type of interpolation (defaults to monotone Fritsch‑Carlson splines, see interpolate), 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 when na.rm = FALSE (see examples).

Value

A numeric vector.

See Also

interpolate interpolateNA

Examples

## Example 1: a short vector with NAs
x = c(NA, 1, 2, 3, NA, NA, 6, 9, 8, NA)

# downsample
print(resample(x, len = 5))  # NAs are propagated
print(resample(x, len = 5, na.rm = TRUE))  # NAs are interpolated
print(resample(x, mult = 1/2, na.rm = TRUE, plot = TRUE)) # same

# 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)

# change the method of interpolation
resample(x, mult = 15, lowPass = FALSE, interpol = 'pchip', plot = TRUE)
resample(x, mult = 15, lowPass = FALSE,
  interpol = interpol_loess(span = .6), plot = TRUE)

## 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 artifacts

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

## End(Not run)

soundgen documentation built on Sept. 20, 2026, 5:07 p.m.