Track short-term cepstral coefficients

Computes the short-term real cepstrum of audio signals via FFT using the libassp C library (Scheffers 2012; Oppenheim and Schafer 2004; Childers et al. 1977) . Output coefficients index quefrency from 0 to FFT_length/2 in steps of 0.5 ms (at the default 40 Hz resolution). Useful for pitch-period detection and spectral tilt estimation.

Usage

trk_cepstrum(listOfFiles, beginTime = 0, centerTime = FALSE, endTime = 0, resolution = 40, fftLength = 0, windowShift = 5, window = "BLACKMAN", toFile = TRUE, explicitExt = "cep", outputDirectory = NULL, assertLossless = NULL, logToFile = FALSE, keepConverted = FALSE, convertOverwrites = FALSE, verbose = TRUE)

Arguments

listOfFiles: Character vector of audio file paths. Any format supported by av is accepted; non-native inputs are transcoded automatically.
resolution: Numeric. Target FFT frequency resolution in Hz; the FFT length is set to the smallest power-of-2 meeting this target. Default 40.0.
fftLength: Integer. Explicit FFT length in points; overrides resolution. Default 0 (use resolution).
beginTime: Start time for the extracted portion in seconds. Default: NULL (beginning of signal). Note: uses beginTime/endTime (seconds) matching DSP function conventions, unlike read_audio() which uses begin/end.
centerTime: Numeric or logical. Single-frame analysis time point in seconds; overrides beginTime, endTime, and windowShift. Default FALSE.
endTime: The end time of the section of the sound files that should be analysed (in seconds). Use 0 for end of file.
windowShift: Numeric. Frame shift in milliseconds; sets output frame rate (1000 / windowShift Hz). Default 5.0 ms (200 Hz). Must be strictly less than 32 ms (the 512-sample analysis window at 16 kHz). Values other than the training default (5 ms) may slightly reduce accuracy.
window: Character. Analysis window function type. Default "BLACKMAN". See AsspWindowTypes for supported types.
toFile: Logical. If TRUE, write SSFF output files and return the count written. If FALSE, return an AsspDataObj (single file only). Default TRUE.
explicitExt: By default, a character "d" will be prepended to the file name suffix when writing the output to file. The user can also specify an explicit extension which will be used instead.
outputDirectory: The directory where the slice file should be stored. If not defiled (NULL), the sparse slice file will placed in the same folder as the media file.
assertLossless: Character vector of additional file extensions to treat as losslessly encoded.
logToFile: Logical. Write processing log to a file in outputDirectory rather than the console. Default FALSE.
keepConverted: Logical. Retain intermediate transcoded files. Default FALSE.
convertOverwrites: Logical. Allow transcoding to overwrite existing files. Default FALSE.
verbose: Logical. Show a progress bar (sequential path) or a progress-aware parallel apply (pbapply/pbmcapply, if installed).

Value

If toFile = FALSE: an AsspDataObj with track:

C[dB]: REAL32, dB amplitude, n_frames x (FFT_length/2 + 1) columns. Each column corresponds to a quefrency of col_index × 0.5 ms.

Frame rate: 1000 / windowShift Hz (default 200 Hz). If toFile = TRUE: integer count of files written, returned invisibly.

Details

The number of coefficients per frame equals FFT_length / 2 + 1 (one-sided, not mirrored). Use fftLength to fix the transform size; otherwise resolution governs it. Pre-emphasis is not applied by this function; apply trk_afdiff first if needed.

References

Childers DG, Skinner DP, Kemerait RC (1977). “The cepstrum: A guide to processing.” Proceedings of the IEEE, 65(10), 1428–1443. ISSN 0018-9219. doi:10.1109/proc.1977.10747 .

Oppenheim AV, Schafer RW (2004). “From frequency to quefrency: a history of the cepstrum.” IEEE Signal Processing Magazine, 21(5), 95–106. ISSN 1053-5888. doi:10.1109/msp.2004.1328092 .

Scheffers M (2012). “Advanced Speech Signal Processor.” https://sourceforge.net/projects/libassp/files/libassp/.

Author

Raphael Winkelmann

Lasse Bombien

Fredrik Nylén

Examples

# get path to audio file
path2wav <- list.files(system.file("samples","sustained", package = "superassp"), pattern = glob2rx("a1.wav"), full.names = TRUE)

# calulate cepstrum
res <- trk_cepstrum(path2wav, toFile=FALSE)
#> Applying `method(trk_cepstrum, class_character)()` to 1 recording

# plot cepstral values at midpoint of signal
plot(y=res[["C[dB]"]][400,],
    x=seq(1,ncol(res[["C[dB]"]])),
    type='l',
    xlab='Quefrency (ms)',
    ylab='Amplitude (dB)')