getRolloff: Control rolloff of harmonics

In tatters/soundgen: Sound Synthesis and Acoustic Analysis

Control rolloff of harmonics

Description

Harmonics are generated as separate sine waves. But we don't want each harmonic to be equally strong, so we normally specify some rolloff function that describes the loss of energy in upper harmonics relative to the fundamental frequency (f0). getRolloff provides flexible control over this rolloff function, going beyond simple exponential decay (rolloff). Use quadratic terms to modify the behavior of a few lower harmonics, rolloffOct to adjust the rate of decay per octave, and rolloffKHz for rolloff correction depending on f0. Plot the output with different parameter values and see examples below and the vignette to get a feel for how to use getRolloff effectively.

Usage

getRolloff(
  pitch_per_gc = c(440),
  nHarmonics = NULL,
  rolloff = -6,
  rolloffOct = 0,
  rolloffParab = 0,
  rolloffParabHarm = 3,
  rolloffParabCeiling = NULL,
  rolloffKHz = 0,
  baseline = 200,
  dynamicRange = 80,
  samplingRate = 16000,
  plot = FALSE
)

Arguments

pitch_per_gc	a vector of f0 per glottal cycle, Hz
nHarmonics	maximum number of harmonics to generate (very weak harmonics with amplitude < -dynamicRange will be discarded)
rolloff	basic rolloff from lower to upper harmonics, db/octave (exponential decay). All rolloff parameters are in anchor format. See getRolloff for more details
rolloffOct	basic rolloff changes from lower to upper harmonics (regardless of f0) by rolloffOct dB/oct. For example, we can get steeper rolloff in the upper part of the spectrum
rolloffParab	an optional quadratic term affecting only the first rolloffParabHarm harmonics. The middle harmonic of the first rolloffParabHarm harmonics is amplified or dampened by rolloffParab dB relative to the basic exponential decay
rolloffParabHarm	the number of harmonics affected by rolloffParab
rolloffParabCeiling	quadratic adjustment is applied only up to rolloffParabCeiling, Hz. If not NULL, it overrides rolloffParabHarm
rolloffKHz	rolloff changes linearly with f0 by rolloffKHz dB/kHz. For ex., -6 dB/kHz gives a 6 dB steeper basic rolloff as f0 goes up by 1000 Hz
baseline	The "neutral" f0, at which no adjustment of rolloff takes place regardless of rolloffKHz
dynamicRange	dynamic range, dB. Harmonics and noise more than dynamicRange under maximum amplitude are discarded to save computational resources
samplingRate	sampling rate (needed to stop at Nyquist frequency and for plotting purposes)
plot	if TRUE, produces a plot

Value

Returns a matrix of amplitude multiplication factors for adjusting the amplitude of harmonics relative to f0 (1 = no adjustment, 0 = silent). Each row of output contains one harmonic, and each column contains one glottal cycle.

See Also

soundgen

Examples

# steady exponential rolloff of -12 dB per octave
rolloff = getRolloff(pitch_per_gc = 150, rolloff = -12,
  rolloffOct = 0, rolloffKHz = 0, plot = TRUE)
# the rate of rolloff slows down by 1 dB each octave
rolloff = getRolloff(pitch_per_gc = 150, rolloff = -12,
  rolloffOct = 1, rolloffKHz = 0, plot = TRUE)

# rolloff can be made to depend on f0 using rolloffKHz
rolloff = getRolloff(pitch_per_gc = c(150, 400, 800),
  rolloffOct = 0, rolloffKHz = -3, plot = TRUE)
# without the correction for f0 (rolloffKHz),
  # high-pitched sounds have the same rolloff as low-pitched sounds,
  # producing unnaturally strong high-frequency harmonics
rolloff = getRolloff(pitch_per_gc = c(150, 400, 800),
  rolloffOct = 0, rolloffKHz = 0, plot = TRUE)

# parabolic adjustment of lower harmonics
rolloff = getRolloff(pitch_per_gc = 350, rolloffParab = 0,
  rolloffParabHarm = 2, plot = TRUE)
# rolloffParabHarm = 1 affects only f0
rolloff = getRolloff(pitch_per_gc = 150, rolloffParab = 30,
  rolloffParabHarm = 1, plot = TRUE)
# rolloffParabHarm=2 or 3 affects only h1
rolloff = getRolloff(pitch_per_gc = 150, rolloffParab = 30,
  rolloffParabHarm = 2, plot = TRUE)
# rolloffParabHarm = 4 affects h1 and h2, etc
rolloff = getRolloff(pitch_per_gc = 150, rolloffParab = 30,
  rolloffParabHarm = 4, plot = TRUE)
# negative rolloffParab weakens lower harmonics
rolloff = getRolloff(pitch_per_gc = 150, rolloffParab = -20,
  rolloffParabHarm = 7, plot = TRUE)
# only harmonics below 2000 Hz are affected
rolloff = getRolloff(pitch_per_gc = c(150, 600),
  rolloffParab = -20, rolloffParabCeiling = 2000,
  plot = TRUE)

# dynamic rolloff (varies over time)
rolloff = getRolloff(pitch_per_gc = c(150, 250),
                     rolloff = c(-12, -18, -24), plot = TRUE)
rolloff = getRolloff(pitch_per_gc = c(150, 250), rolloffParab = 40,
                    rolloffParabHarm = 1:5, plot = TRUE)

## Not run: 
# Note: getRolloff() is called internally by soundgen()
# using the data.frame format for all vectorized parameters
# Compare:
s1 = soundgen(sylLen = 1000, pitch = 250,
              rolloff = c(-24, -2, -18), plot = TRUE)
s2 = soundgen(sylLen = 1000, pitch = 250,
              rolloff = data.frame(time = c(0, .2, 1),
                                   value = c(-24, -2, -18)),
              plot = TRUE)

# Also works for rolloffOct, rolloffParab, etc:
s3 = soundgen(sylLen = 1000, pitch = 250,
             rolloffParab = 20, rolloffParabHarm = 1:15, plot = TRUE)

## End(Not run)

tatters/soundgen documentation built on Aug. 22, 2023, 4:24 p.m.