getRolloff: Rolloff of harmonics in source spectrum

In soundgen: Sound Synthesis and Acoustic Analysis

Rolloff of harmonics in source spectrum

Description

A periodic sound often contains many harmonics of the fundamental frequency (f0). For instance, soundgen generates voice source as a combination of pure tones - one for each partial in the source spectrum. Harmonics typically become weaker at higher frequencies, and the rolloff (roll-off) function describes the loss of energy in upper harmonics relative to f0. getRolloff provides flexible control over this rolloff function: simple exponential (rolloff), rolloffOct that varies per octave, and rolloffKHz for rolloff correction depending on f0. It calculates the rolloff function based on these parameters and returns the amplitude of each harmonic.

Usage

getRolloff(
  pitch_per_gc = c(440),
  nHarmonics = 1000,
  rolloff = -6,
  rolloffOct = 0,
  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 or partials to generate, including f0 (all harmonics above Nyquist frequency or with amplitude < -dynamicRange are discarded)
rolloff	the rate at which f0 harmonics in the spectrum become weaker, dB/oct (anchor format for all rolloff-related parameters). More negative rolloff = weaker upper harmonics
rolloffOct, rolloffKHz	rolloff may be constant throughout the spectrum, or it may vary with each octave above f0 (rolloffOct) or per kHz increase in f0 above the baseline of 200 Hz (rolloffKHz); for both parameters, positive values mean the rate of rolloff increases toward upper frequencies)
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

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
rolloff1 = getRolloff(pitch_per_gc = 150, rolloff = -12,
  rolloffOct = 0, rolloffKHz = 0, plot = TRUE)
# the rate of rolloff slows down by 1 dB each octave
r = getRolloff(pitch_per_gc = 100, rolloff = -6, rolloffOct = 0)
r1 = getRolloff(pitch_per_gc = 100, rolloff = -6, rolloffOct = -1)
round(20*log10(r[c(1, 2, 4, 8, 16)]), 1)
round(20*log10(r1[c(1, 2, 4, 8, 16)]), 1)

# 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)

# dynamic rolloff (varies over time)
rolloff = getRolloff(pitch_per_gc = c(150, 250),
                     rolloff = c(-12, -18, -24), plot = TRUE)

soundgen documentation built on Sept. 20, 2026, 5:07 p.m.