generateNoise: Generate noise

Description

Generates noise of length len and with spectrum defined by rolloff parameters OR by a specified filter formantFilter. This function is called internally by soundgen, but it may be more convenient to call it directly when synthesizing non-biological noises defined by specific spectral and amplitude envelopes rather than formants: the wind, whistles, impact noises, etc. See beat for similarly simplified functions for tonal non-biological sounds.

Usage

generateNoise(
  len,
  rolloffNoise = -4,
  noiseFlatSpec = 1200,
  rolloffNoiseExp = 0,
  formantFilter = NULL,
  noise = NULL,
  attackLen = 10,
  samplingRate = 16000,
  windowLength = 50,
  step = NULL,
  overlap = 75,
  wn = "gaussian",
  smoothing = list(),
  play = FALSE
)

Value

The generated waveform as a numeric vector.

Arguments

len: length of output, samples
rolloffNoise, rolloffNoiseExp, noiseFlatSpec: linear (rolloffNoise, dB/kHz, anchor format) or exponential (rolloffNoiseExp, dB/oct, anchor format) rolloff of the excitation source for the noise component (anchor format) applied above noiseFlatSpec (Hz, scalar). More negative rolloff = less high-frequency noise
formantFilter: (optional): as an alternative to using rolloffNoise, we can provide the exact filter - a vector of non-negative numbers specifying the desired spectrum on a linear scale up to Nyquist frequency. The length doesn't matter as it can be interpolated internally. A matrix specifying time-varying filter for each STFT step is also accepted: frequencies in rows, STFT frames in columns. The easiest way to obtain formantFilter is to call getFormantFilter or to use (smoothed) spectrum / spectrogram of an existing sound
noise: intensity of turbulent noise (0 dB = same RMS as that of the periodic (voiced) component, negative values = less intense; anchor format). In soundgen 3.0, the noise component is always calibrated relative to the filtered harmonic component. When noise is present, the harmonic and noise components are filtered separately, their RMS amplitudes are normalized after filtering, and they are then mixed. Because noise can begin before the voiced part and continue after it, the time of noise anchors MUST be in ms, not [0, 1]; this is different from all other soundgen arguments that accept the anchor format with time either in ms or [0, 1]
attackLen: duration of fade-in / fade-out at each end of syllables and noise (ms): a vector of length 1 (symmetric) or 2 (separately for fade-in and fade-out)
samplingRate: sampling rate of the output (Hz)
windowLength: length of the FFT window (ms)
step: step between successive windows (ms); if provided, overrides overlap
overlap: overlap between successive windows (0–100%)
wn: wn window type accepted by winFun: character string or function
smoothing: a list of parameters passed to interpolate to control the interpolation and smoothing of contours drawn through anchors
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

Details

Algorithm: paints a spectrogram with desired characteristics, sets phase to zero, and generates a time sequence via inverse FFT.

Examples

Run this code

# .5 s of white noise
samplingRate = 16000
noise1 = soundgen:::generateNoise(len = samplingRate * .5,
  samplingRate = samplingRate)
meanSpectrum(noise1, samplingRate)
# playme(noise1, samplingRate)

# Percussion (run a few times to notice stochasticity due to temperature = .25)
noise2 = soundgen:::generateNoise(len = samplingRate * .15, noise = c(0, -80),
  rolloffNoise = c(4, -6), attackLen = 5)
noise3 = soundgen:::generateNoise(len = samplingRate * .25, noise = c(0, -40),
  rolloffNoise = c(4, -20), attackLen = 5)
# playme(c(noise2, noise3), samplingRate)

if (FALSE) {
playback = list(TRUE, FALSE, 'aplay', 'vlc')[[1]]
# 1.2 s of noise with rolloff changing from 0 to -12 dB above 2 kHz
noise = generateNoise(len = samplingRate * 1.2,
  rolloffNoise = c(0, -12), noiseFlatSpec = 2000,
  samplingRate = samplingRate, play = playback)
# spectrogram(noise, samplingRate)

# Similar, but using the dataframe format to specify a more complicated
# contour for rolloffNoise:
noise = generateNoise(len = samplingRate * 1.2,
  rolloffNoise = data.frame(time = c(0, .3, 1), value = c(-12, 0, -12)),
  noiseFlatSpec = 2000, samplingRate = samplingRate, play = playback)
# spectrogram(noise, samplingRate)

# To create a sibilant [s], specify a single strong, broad formant at ~7 kHz:
wl = 1024
formantFilter = getFormantFilter(
  nr = wl %/% 2 + 1, nc = 1, samplingRate = samplingRate,
 formants = list('f1' = data.frame(time = 0, freq = 7000,
                                   amp = 50, width = 2000)))
noise = fade(generateNoise(len = samplingRate,
  samplingRate = samplingRate, formantFilter = as.numeric(formantFilter),
  play = playback), samplingRate = samplingRate)
# plot(formantFilter, type = 'l')
meanSpectrum(noise, samplingRate)

# Low-frequency, wind-like noise
formantFilter = getFormantFilter(
  nr = 50, nc = 1, lipRad = 0,
  samplingRate = samplingRate, formants = list('f1' = list(
    freq = 250, amp = 30, width = 150)),
    formantDepStoch = 0, plot = TRUE)
noise = fade(generateNoise(len = samplingRate,
  samplingRate = samplingRate, formantFilter = as.numeric(formantFilter),
  play = playback))
spectrogram(noise, samplingRate, ylim = c(0, 2))

# Manual filter, e.g. for a kettle-like whistle (narrow-band noise)
formantFilter = c(rep(0, 100), 120, rep(0, 100))  # any length is fine
# plot(formantFilter, type = 'b')  # narrow-band filter at Nyquist / 2, here 4 kHz
noise = fade(generateNoise(len = samplingRate, formantFilter = formantFilter,
  samplingRate = samplingRate, play = playback))
spectrogram(noise, samplingRate)

# Compare to a similar sound created with soundgen()
# (aperiodic noise only, a single formant at 4 kHz)
noise_s = soundgen(pitch = NULL,
  noise = data.frame(time = c(0, 1000), value = c(0, 0)),
  formants = list(f1 = data.frame(freq = 4000, amp = 80, width = 20)),
  play = playback)
}