soundgen (version 3.0.0)

timeStretch: Time stretch

Description

Dynamically time-stretches a sound without preserving its pitch or formants, as if gradually changing playback speed. Algorithm: the audio is resampled at time-varying steps. This is about 100 times faster than time-stretching with a phase vocoder in shiftPitch, but pitch and formants cannot be preserved, and compressing the sound (stretch < 1) may cause artifacts due to aliasing, since no anti-aliasing filter is applied (low-pass filter the input and/or output if needed). The stretch contour is interpreted over the output (stretched) duration, which is why the trajectory differs from shiftPitch with the same anchors.

Usage

timeStretch(
  x,
  stretch = 1,
  samplingRate = NULL,
  interpol = "splineFC",
  precision = 1000,
  play = FALSE,
  saveAudio = FALSE,
  reportEvery = NULL,
  cores = 1
)

Value

The processed waveform as a numeric vector for a single input or a list for multiple outputs. The duration is approximate: the output may end up a few samples shorter than intended if the resampling trajectory reaches the end of the input.

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

stretch

1 = no change, >1 = longer, <1 = shorter. Single value, vector, or anchor format (see soundgen). Must be positive

samplingRate

sampling rate of x (only needed if x is a numeric vector)

interpol

interpolation method supported by interpolate

precision

the number of points used for estimating the duration of output (more = better, but slower)

play

if TRUE, plays the output audio using the default player on your system. If a character string, it is passed to playme as the name of the player to use (e.g. 'aplay', 'play', 'vlc'). In case of errors, try setting another default player for playme

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

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

See Also

shiftPitch

Examples

data(speechEx, package = 'soundgen')  # import a recording
# playme(speechEx)
# spectrogram(speechEx)
s1 = timeStretch(speechEx, stretch = c(1, 3))
# playme(s1, [email protected])
# spectrogram(s1, [email protected])

# compare to a similar effect achieved with a phase vocoder in shiftPitch():
s2 = shiftPitch(
  speechEx,
  timeStretch = c(1, 3),  # from 1 (original) to mult
  multPitch = c(1, 1/3),  # also drop pitch
  multFormants = c(1, 1/3)  # also drop formants (by the same proportion)
)
# playme(s2, [email protected])
# spectrogram(s2, [email protected])
# NB: because the two algorithms calculate transitions between stretch
# factors in different ways, the duration is not identical, even though the
# range of pitch change is the same