soundgen (version 1.3.0)

addFormants: Add formants

Description

A spectral filter that either adds or removes formants from a sound - that is, amplifies or dampens certain frequency bands, as in human vowels. See soundgen and getSpectralEnvelope for more information. With action = 'remove' this function can perform inverse filtering to remove formants and obtain raw glottal output, provided that you can specify the correct formant structure.

Usage

addFormants(sound, formants, action = c("add", "remove")[1],
  vocalTract = NA, formantDep = 1, formantDepStoch = 20,
  formantWidth = 1, lipRad = 6, noseRad = 4, mouthOpenThres = 0,
  mouthAnchors = NA, interpol = c("approx", "spline", "loess")[3],
  temperature = 0.025, formDrift = 0.3, formDisp = 0.2,
  samplingRate = 16000, windowLength_points = 800, overlap = 75,
  normalize = TRUE)

Arguments

sound

numeric vector with samplingRate

formants

either a character string like "aaui" referring to default presets for speaker "M1" or a list of formant times, frequencies, amplitudes, and bandwidths (see ex. below). formants = NA defaults to schwa. Time stamps for formants and mouthOpening can be specified in ms or an any other arbitrary scale. See getSpectralEnvelope for more details

action

'add' = add formants to the sound, 'remove' = remove formants (inverse filtering)

vocalTract

the length of vocal tract, cm. Used for calculating formant dispersion (for adding extra formants) and formant transitions as the mouth opens and closes. If NULL or NA, the length is estimated based on specified formant frequencies (if any)

formantDep

scale factor of formant amplitude (1 = no change relative to amplitudes in formants)

formantDepStoch

the amplitude of additional stochastic formants added above the highest specified formant, dB (only if temperature > 0)

formantWidth

= scale factor of formant bandwidth (1 = no change)

lipRad

the effect of lip radiation on source spectrum, dB/oct (the default of +6 dB/oct produces a high-frequency boost when the mouth is open)

noseRad

the effect of radiation through the nose on source spectrum, dB/oct (the alternative to lipRad when the mouth is closed)

mouthOpenThres

open the lips (switch from nose radiation to lip radiation) when the mouth is open >mouthOpenThres, 0 to 1

mouthAnchors

mouth opening (0 to 1, 0.5 = neutral, i.e. no modification) (anchor format)

interpol

the method of smoothing envelopes based on provided mouth anchors: 'approx' = linear interpolation, 'spline' = cubic spline, 'loess' (default) = polynomial local smoothing function. NB: this does NOT affect the smoothing of formant anchors

temperature

hyperparameter for regulating the amount of stochasticity in sound generation

formDrift, formDisp

scaling factors for the effect of temperature on formant drift and dispersal, respectively

samplingRate

sampling frequency, Hz

windowLength_points

length of FFT window, points

overlap

FFT window overlap, %. For allowed values, see istft

normalize

if TRUE, normalizes the output to range from -1 to +1

Details

Algorithm: converts input from a time series (time domain) to a spectrogram (frequency domain) through short-term Fourier transform (STFT), multiples by the spectral filter containing the specified formants, and transforms back to a time series via inverse STFT. This is a subroutine in soundgen, but it can also be used on any existing sound.

Examples

# NOT RUN {
sound = c(rep(0, 1000), runif(16000), rep(0, 1000))  # white noise
# NB: pad with silence to avoid artefacts if removing formants
# playme(sound)
# spectrogram(sound, samplingRate = 16000)

# add F1 = 900, F2 = 1300 Hz
sound_filtered = addFormants(sound, formants = c(900, 1300))
# playme(sound_filtered)
# spectrogram(sound_filtered, samplingRate = 16000)

# ...and remove them again (assuming we know what the formants are)
sound_inverse_filt = addFormants(sound_filtered,
                                 formants = c(900, 1300),
                                 action = 'remove')
# playme(sound_inverse_filt)
# spectrogram(sound_inverse_filt, samplingRate = 16000)
# }