shiftFormants: Shift formants
In soundgen: Sound Synthesis and Acoustic Analysis

shiftFormants

R Documentation

Shift formants

Description

Raises or lowers formants (resonance frequencies), changing the voice quality or timbre of the sound without changing its pitch, statically or dynamically. Note that this is only possible when the fundamental frequency f0 is lower than the formant frequencies. For best results, freqWindow should be no lower than f0 and no higher than formant bandwidths. Obviously, this is impossible for many signals, so just try a few reasonable values, like ~200 Hz for speech. If freqWindow is not specified, soundgen sets it to the average detected f0, which is slow.

Usage

shiftFormants(
  x,
  multFormants,
  samplingRate = NULL,
  freqWindow = NULL,
  dynamicRange = 80,
  windowLength = 50,
  step = NULL,
  overlap = 75,
  wn = "gaussian",
  interpol = c("approx", "spline")[1],
  normalize = c("max", "orig", "none")[2],
  play = FALSE,
  saveAudio = NULL,
  reportEvery = NULL,
  cores = 1,
  ...
)

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
`multFormants`	1 = no change, >1 = raise formants (eg 1.1 = 10% up, 2 = one octave up), <1 = lower formants. Anchor format accepted (see `soundgen`)
`samplingRate`	sampling rate of `x` (only needed if `x` is a numeric vector)
`freqWindow`	the width of spectral smoothing window, Hz. Defaults to detected f0
`dynamicRange`	dynamic range, dB. All values more than one dynamicRange under maximum are treated as zero
`windowLength`	length of FFT window, ms
`step`	you can override `overlap` by specifying FFT step, ms (NB: because digital audio is sampled at discrete time intervals of 1/samplingRate, the actual step and thus the time stamps of STFT frames may be slightly different, eg 24.98866 instead of 25.0 ms)
`overlap`	overlap between successive FFT frames, %
`wn`	window type accepted by `ftwindow`, currently gaussian, hanning, hamming, bartlett, blackman, flattop, rectangle
`interpol`	the method for interpolating scaled spectra
`normalize`	"orig" = same as input (default), "max" = maximum possible peak amplitude, "none" = no normalization
`play`	if TRUE, plays the synthesized sound using the default player on your system. If character, passed to `play` as the name of player to use, eg "aplay", "play", "vlc", etc. In case of errors, try setting another default player for `play`
`saveAudio`	full path to the folder in which to save audio files (one per detected syllable)
`reportEvery`	when processing multiple inputs, report estimated time left every ... iterations (NULL = default, NA = don't report)
`cores`	number of cores for parallel processing
`...`	other graphical parameters

Details

Algorithm: phase vocoder. In the frequency domain, we separate the complex spectrum of each STFT frame into two parts. The "receiver" is the flattened or smoothed complex spectrum, where smoothing is achieved by obtaining a smoothed magnitude envelope (the amount of smoothing is controlled by freqWindow) and then dividing the complex spectrum by this envelope. This basically removes the formants from the signal. The second component, "donor", is a scaled and interpolated version of the same smoothed magnitude envelope as above - these are the formants shifted up or down. Warping can be easily implemented instead of simple scaling if nonlinear spectral transformations are required. We then multiply the "receiver" and "donor" spectrograms and reconstruct the audio with iSTFT.

Examples

s = soundgen(sylLen = 200, ampl = c(0,-10),
             pitch = c(250, 350), rolloff = c(-9, -15),
             noise = -40,
             formants = 'aii', addSilence = 50)
# playme(s)
s1 = shiftFormants(s, samplingRate = 16000, multFormants = 1.25,
                   freqWindow = 200)
# playme(s1)

## Not run: 
data(sheep, package = 'seewave')  # import a recording from seewave
playme(sheep)
spectrogram(sheep)

# Lower formants by 4 semitones or ~20% = 2 ^ (-4 / 12)
sheep1 = shiftFormants(sheep, multFormants = 2 ^ (-4 / 12), freqWindow = 150)
playme(sheep1, sheep@samp.rate)
spectrogram(sheep1, sheep@samp.rate)

orig = seewave::meanspec(sheep, wl = 128, plot = FALSE)
shifted = seewave::meanspec(sheep1, wl = 128, f = sheep@samp.rate, plot = FALSE)
plot(orig[, 1], log(orig[, 2]), type = 'l')
points(shifted[, 1], log(shifted[, 2]), type = 'l', col = 'blue')

# dynamic change: raise formants at the beginning, lower at the end
sheep2 = shiftFormants(sheep, multFormants = c(1.3, .7), freqWindow = 150)
playme(sheep2, sheep@samp.rate)
spectrogram(sheep2, sheep@samp.rate)

## End(Not run)

soundgen documentation built on Sept. 12, 2024, 6:29 a.m.