83 lines
2.3 KiB
Rust
83 lines
2.3 KiB
Rust
// nih-plug: plugins, but rewritten in Rust
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// Copyright (C) 2022 Robbert van der Helm
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <https://www.gnu.org/licenses/>.
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pub const MINUS_INFINITY_DB: f32 = -100.0;
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/// Convert decibels to a voltage gain ratio, treating anything below -100 dB as minus infinity.
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pub fn db_to_gain(dbs: f32) -> f32 {
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if dbs > MINUS_INFINITY_DB {
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10.0f32.powf(dbs * 0.05)
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} else {
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0.0
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}
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}
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/// Convert a voltage gain ratio to decibels. Gain ratios that aren't positive will be treated as
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/// [MINUS_INFINITY_DB].
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pub fn gain_to_db(gain: f32) -> f32 {
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if gain > 0.0 {
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gain.log10() * 20.0
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} else {
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MINUS_INFINITY_DB
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}
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}
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/// Convert a MIDI note ID to a frequency at A4 = 440 Hz equal temperament and middle C = note 60 =
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/// C4.
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pub fn midi_note_to_freq(pitch: u8) -> f32 {
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2.0f32.powf((pitch as f32 - 69.0) / 12.0) * 440.0
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_db_to_gain_positive() {
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assert_eq!(db_to_gain(3.0), 1.4125376);
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}
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#[test]
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fn test_db_to_gain_negative() {
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assert_eq!(db_to_gain(-3.0), 1.4125376f32.recip());
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}
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#[test]
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fn test_db_to_gain_minus_infinity() {
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assert_eq!(db_to_gain(-100.0), 0.0);
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}
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#[test]
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fn test_gain_to_db_positive() {
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assert_eq!(gain_to_db(4.0), 12.041201);
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}
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#[test]
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fn test_gain_to_db_negative() {
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assert_eq!(gain_to_db(0.25), -12.041201);
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}
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#[test]
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fn test_gain_to_db_minus_infinity_zero() {
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assert_eq!(gain_to_db(0.0), MINUS_INFINITY_DB);
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}
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#[test]
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fn test_gain_to_db_minus_infinity_negative() {
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assert_eq!(gain_to_db(-2.0), MINUS_INFINITY_DB);
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}
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}
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