crossFade: Join two waveforms by cross-fading
In tatters/soundgen_beta: Parametric Voice Synthesis

Description Usage Arguments Value Examples

crossFade joins two input vectors (waveforms) by cross-fading. 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.

1	crossFade(ampl1, ampl2, samplingRate, crossLen = 15, crossLenPoints = NULL)

`ampl1, ampl2`	two numeric vectors (waveforms) to be joined
`samplingRate`	the sampling rate of input vectors, Hz
`crossLen`	the length of overlap, in ms (doesn't need to be specified if crossLenPoints is not NULL)
`crossLenPoints`	(optional) the length of overlap, in points (defaults to NULL)

Returns a numeric vector.

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