R/note2freq.R

In egenn/music: Learn and Experiment with Music Theory

# note2freq.R
# ::music::
# 2019 E.D. Gennatas lambdamd.org

rt_octave <- c("C", "Db", "D", "Eb", "E", "F", "Gb", "G", "Ab", "A", "Bb", "B")
rt_notes <- c(t(sapply(rt_octave, function(i) paste0(i, -2:8))))[-c(129:132)]
rt_pos <- seq(rt_notes)
names(rt_pos) <- rt_notes

#' Convert musical notes to frequencies
#'
#' Convert notes to frequencies
#'
#' @param note String: Note(s) to convert to frequencies
#' @param tuning String: "12ET": 12-note equal temperament, "custom": 
#' Intonation defined by \code{customRatios}
#' @param custom.ratios Numeric, vector, length 13: Custom ratios for a 12-note 
#' scale, starting with 1 (root) and ending in 2 (octave) to use when 
#' \code{tuning = "custom"}. The A4 note will be set to \code{A4} Hz and the
#' rest of the frequencies will be built based on these ratios and the 
#' \code{customRoot}
#' @param A4 Float: Frequency for A4 in Hz. Default = 440
#' @param custom.root String: Root note for just intonation 
#' (\code{tuning = "custom"}). Default = "C"
#' @param default.octave Integer: If \code{note} is provided without octave 
#' number (e.g. "C"), default to this octave. Default = 4
#'
#' @examples
#' note2freq(buildScale("B4", "minor"))
#' @author E.D. Gennatas
#' @export

note2freq <- function(note,
                      tuning = c("12ET", "custom"),
                      custom.ratios = c(1, 16 / 15, 9 / 8, 6 / 5, 5 / 4, 4 / 3, 45 / 32, 3 / 2, 8 / 5, 5 / 3, 9 / 5, 15 / 8, 2),
                      A4 = 440,
                      custom.root = "C",
                      default.octave = 4) {
    tuning <- match.arg(tuning)
    .notes <- formatNote(note, default.octave = default.octave)

    if (tuning == "12ET") {
        rt_semitones <- rt_pos - rt_pos["A4"]
        .frequencies <- A4 * 2^(rt_semitones / 12)
    } else if (tuning == "custom") {
        custom.root <- formatNote(custom.root)
        rt_semitones <- rt_pos - rt_pos[custom.root]
        .octaves <- 2^floor(rt_semitones / 12)
        .index <- rt_semitones %% 12 + 1
        A4.index <- noteDistance(c(custom.root, "A4"))[2] + 1
        .root.freq <- solve(custom.ratios[A4.index], A4)
        .frequencies <- .root.freq * .octaves * custom.ratios[.index]
    }

    .freqs <- .frequencies[.notes]
    names(.freqs) <- .notes
    .freqs
} # music::note2freq