normalizeFolder: Normalize folder

In soundgen: Sound Synthesis and Acoustic Analysis

Normalize folder

Description

Normalizes the amplitude of all wav/mp3 files in a folder based on their peak or RMS amplitude or subjective loudness. This is good for playback experiments, which require that all sounds should have similar intensity or loudness. If preserveRelativeDif is set to TRUE, all recordings in the target folder get a boost in amplitude, so the loudest one reaches maxAmp, but the relative differences between the recordings are preserved (i.e., all files are boosted by the same amount - as much as possible to avoid clipping the loudest one).

Usage

normalizeFolder(
  myfolder,
  type = c("peak", "rms", "loudness"),
  maxAmp = 0,
  summaryFun = "mean",
  preserveRelativeDif = FALSE,
  windowLength = 50,
  step = NULL,
  overlap = 70,
  killDC = FALSE,
  windowDC = 200,
  cores = 1,
  savePath = NULL,
  reportEvery = NULL
)

Arguments

myfolder	full path to folder containing input audio files
type	normalize so the output files have the same peak amplitude ('peak'), root mean square amplitude ('rms'), or subjective loudness in sone ('loudness')
maxAmp	maximum amplitude in dB (0 = max possible, -10 = 10 dB below max possible, etc.)
summaryFun	should the output files have the same mean / median / max etc RMS amplitude or loudness? (summaryFun has no effect if type = 'peak')
preserveRelativeDif	(only for type = "peak") if FALSE (default), all files are normalized to the same level; if TRUE, the peak amplitude of the loudest file is set to maxAmp, while the remaining files are quieter so the original relative peak amplitude across files is preserved
windowLength	length of analysis window, ms (longer windows = more smoothing)
step	step between successive windows, ms; if provided, overrides overlap; 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 - e.g., 24.98866 instead of 25.0 ms
overlap	overlap between successive windows, %
killDC	if TRUE, removes DC offset (see also flatEnv)
windowDC	the window for calculating DC offset, ms
cores	number of cores for parallel processing
savePath	full path to where the normalized files should be saved; defaults to NULL = 'myfolder/normalized'; NA = do not save the processed files
reportEvery	when processing multiple inputs, report estimated time left every reportEvery iterations (NULL = default, NA = don't report); see reportTime

Details

Algorithm: first all files are rescaled to have the same peak amplitude of maxAmp dB. If type = 'peak', the process ends here. If type = 'rms', there are two additional steps. First the original RMS amplitude of all files is calculated per frame by getRMS. The "quietest" sound with the lowest summary RMS value is not modified, so its peak amplitude remains maxAmp dB. All the remaining sounds are rescaled linearly, so that their summary RMS values becomes the same as that of the "quietest" sound, and their peak amplitudes become smaller, <maxAmp. Finally, if type = 'loudness', the subjective loudness of each sound is estimated by getLoudness, which assumes frequency sensitivity typical of human hearing. The following normalization procedure is similar to that for type = 'rms'. NB: because loudness is not a simple linear function of SPL, loudness normalization is only approximate; reiterate the process several times to improve the precision of loudness normalization.

Value

Does not return anything, only saves the normalized audio files.

See Also

getRMS analyze getLoudness

Examples

## Not run: 
# put a few short audio files in a folder, eg '~/Downloads/temp'
target = '~/Downloads/temp'
save_in_folder = paste0(target, '/normalized')
getRMS(target, summaryFun = 'mean')$summary  # different
normalizeFolder(target, type = 'rms', summaryFun = 'mean',
  savePath = save_in_folder)
getRMS(save_in_folder, summaryFun = 'mean')$summary  # same
# If the saved audio files are treated as stereo with one channel missing,
# try reconverting with ffmpeg (saving is handled by tuneR::writeWave)

## End(Not run)

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