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/*
* Copyright 1998 Phil Burk, Mobileer Inc
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.softsynth.math;
/**
* Miscellaneous math functions useful in Audio
*
* @author (C) 1998 Phil Burk
*/
public class AudioMath {
// use scalar to convert natural log to log_base_10
private final static double a2dScalar = 20.0 / Math.log(10.0);
public static final int CONCERT_A_PITCH = 69;
public static final double CONCERT_A_FREQUENCY = 440.0;
private static double mConcertAFrequency = CONCERT_A_FREQUENCY;
/**
* Convert amplitude to decibels. 1.0 is zero dB. 0.5 is -6.02 dB.
*/
public static double amplitudeToDecibels(double amplitude) {
double db = Math.log(amplitude) * a2dScalar;
return db;
}
/**
* Convert decibels to amplitude. Zero dB is 1.0 and -6.02 dB is 0.5.
*/
public static double decibelsToAmplitude(double decibels) {
double amp = Math.pow(10.0, decibels / 20.0);
return amp;
}
/**
* Calculate MIDI pitch based on frequency in Hertz. Middle C is 60.0.
*/
public static double frequencyToPitch(double frequency) {
return CONCERT_A_PITCH + 12 * Math.log(frequency / mConcertAFrequency) / Math.log(2.0);
}
/**
* Calculate frequency in Hertz based on MIDI pitch. Middle C is 60.0. You can use fractional
* pitches so 60.5 would give you a pitch half way between C and C#.
*/
public static double pitchToFrequency(double pitch) {
return mConcertAFrequency * Math.pow(2.0, ((pitch - CONCERT_A_PITCH) * (1.0 / 12.0)));
}
/**
* This can be used to globally adjust the tuning in JSyn from Concert A at 440.0 Hz to
* a slightly different frequency. Some orchestras use a higher frequency, eg. 441.0.
* This value will be used by pitchToFrequency() and frequencyToPitch().
*
* @param concertAFrequency
*/
public static void setConcertAFrequency(double concertAFrequency) {
mConcertAFrequency = concertAFrequency;
}
public static double getConcertAFrequency() {
return mConcertAFrequency;
}
/** Convert a delta value in semitones to a frequency multiplier.
* @param semitones
* @return scaler For example 2.0 for an input of 12.0 semitones.
*/
public static double semitonesToFrequencyScaler(double semitones) {
return Math.pow(2.0, semitones / 12.0);
}
}
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