crossFade: Join two waveforms by cross-fading

Description Usage Arguments Value Examples

View source: R/postprocessing.R

Description

crossFade joins two input vectors (waveforms) by cross-fading. First it truncates both input vectors, so that ampl1 ends with a zero crossing and ampl2 starts with a zero crossing, both on an upward portion of the soundwave. Then it cross-fades both vectors linearly with an overlap of crossLen or crossLenPoints. If the input vectors are too short for the specified length of cross-faded region, the two vectors are concatenated at zero crossings instead of cross-fading. Soundgen uses crossFade for gluing together epochs with different regimes of pitch effects (see the vignette on sound generation), but it can also be useful for joining two separately generated sounds without audible artifacts.

Usage

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crossFade(ampl1, ampl2, crossLenPoints = 240, crossLen = NULL,
  samplingRate = NULL, shape = c("lin", "exp", "log", "cos",
  "logistic")[1], steepness = 1)

Arguments

ampl1, ampl2

two numeric vectors (waveforms) to be joined

crossLenPoints

(optional) the length of overlap in points

crossLen

the length of overlap in ms (overrides crossLenPoints)

samplingRate

the sampling rate of input vectors, Hz (needed only if crossLen is given in ms rather than points)

shape

controls the type of fade function: 'lin' = linear, 'exp' = exponential, 'log' = logarithmic, 'cos' = cosine, 'logistic' = logistic S-curve

steepness

scaling factor regulating the steepness of fading curves if the shape is 'exp', 'log', or 'logistic' (0 = linear, >1 = steeper than default)

Value

Returns a numeric vector.

Examples

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sound1 = sin(1:100 / 9)
sound2 = sin(7:107 / 3)
plot(c(sound1, sound2), type = 'b')
# an ugly discontinuity at 100 that will make an audible click

sound = crossFade(sound1, sound2, crossLenPoints = 5)
plot(sound, type = 'b') # a nice, smooth transition
length(sound) # but note that cross-fading costs us ~60 points
#  because of trimming to zero crossings and then overlapping

## Not run: 
# Actual sounds, alternative shapes of fade-in/out
sound3 = soundgen(formants = 'a', pitch = 200,
                  addSilence = 0, attackLen = c(50, 0))
sound4 = soundgen(formants = 'u', pitch = 200,
                  addSilence = 0, attackLen = c(0, 50))

# simple concatenation (with a click)
playme(c(sound3, sound4), 16000)

# concatentation from zc to zc (no click, but a rough transition)
playme(crossFade(sound3, sound4, crossLen = 0), 16000)

# linear crossFade over 35 ms - brief, but smooth
playme(crossFade(sound3, sound4, crossLen = 35, samplingRate = 16000), 16000)

# s-shaped cross-fade over 300 ms (shortens the sound by ~300 ms)
playme(crossFade(sound3, sound4, samplingRate = 16000,
                 crossLen = 300, shape = 'cos'), 16000)

## End(Not run)

soundgen documentation built on Oct. 4, 2018, 9:04 a.m.