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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) {
+        return Math.log(amplitude) * a2dScalar;
+    }
+
+    /**
+     * Convert decibels to amplitude. Zero dB is 1.0 and -6.02 dB is 0.5.
+     */
+    public static double decibelsToAmplitude(double decibels) {
+        return Math.pow(10.0, decibels / 20.0);
+    }
+
+    /**
+     * 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);
+    }
+}