SoundFilters.cs

using System;
 
namespace Barotrauma.Sounds
{
    /* This code is adapted from CSCore (.NET Audio Library) which is under a Microsoft Public License (Ms-PL) license.*/
 
    /*
    Microsoft Public License (Ms-PL)
 
    This license governs use of the accompanying software. If you use the software, you accept this license. If you do not accept the license, do not use the software.
 
    1. Definitions
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    A "contribution" is the original software, or any additions or changes to the software.
 
    A "contributor" is any person that distributes its contribution under this license.
 
    "Licensed patents" are a contributor's patent claims that read directly on its contribution.
 
    2. Grant of Rights
    (A) Copyright Grant- Subject to the terms of this license, including the license conditions and limitations in section 3, each contributor grants you a non-exclusive, worldwide, royalty-free copyright license to reproduce its contribution, prepare derivative works of its contribution, and distribute its contribution or any derivative works that you create.
 
    (B) Patent Grant- Subject to the terms of this license, including the license conditions and limitations in section 3, each contributor grants you a non-exclusive, worldwide, royalty-free license under its licensed patents to make, have made, use, sell, offer for sale, import, and/or otherwise dispose of its contribution in the software or derivative works of the contribution in the software.
 
    3. Conditions and Limitations
    (A) No Trademark License- This license does not grant you rights to use any contributors' name, logo, or trademarks.
 
    (B) If you bring a patent claim against any contributor over patents that you claim are infringed by the software, your patent license from such contributor to the software ends automatically.
 
    (C) If you distribute any portion of the software, you must retain all copyright, patent, trademark, and attribution notices that are present in the software.
 
    (D) If you distribute any portion of the software in source code form, you may do so only under this license by including a complete copy of this license with your distribution. If you distribute any portion of the software in compiled or object code form, you may only do so under a license that complies with this license.
 
    (E) The software is licensed "as-is." You bear the risk of using it. The contributors give no express warranties, guarantees or conditions. You may have additional consumer rights under your local laws which this license cannot change. To the extent permitted under your local laws, the contributors exclude the implied warranties of merchantability, fitness for a particular purpose and non-infringement. 
    */
 
    /*
    * These implementations are based on http://www.earlevel.com/main/2011/01/02/biquad-formulas/
    */
 
    public abstract class BiQuad
    {
        protected double A0;
        protected double A1;
        protected double A2;
        protected double B1;
        protected double B2;
 
        protected readonly double _q;
        protected readonly double _gainDB;
        protected double Z1;
        protected double Z2;
 
        protected readonly double _frequency;
 
        protected readonly int _sampleRate;
 
        protected static readonly double DefaultQ = 1.0 / Math.Sqrt(2);
        protected const double DefaultGainDb = 6.0;
 
        protected BiQuad(int sampleRate, double frequency, double q, double gainDb)
        {
            if (sampleRate <= 0)
            {
                throw new ArgumentOutOfRangeException("sampleRate");
            }
            if (frequency <= 0)
            {
                throw new ArgumentOutOfRangeException("frequency");
            }
            if (q <= 0)
            {
                throw new ArgumentOutOfRangeException("q");
            }
            if (sampleRate < frequency * 2)
            {
                throw new ArgumentOutOfRangeException("sampleRate", "The sample rate has to be greater than or equal to 2 * frequency.");
            }
            _sampleRate = sampleRate;
            _frequency = frequency;
            _q = q;
            _gainDB = gainDb;
            CalculateBiQuadCoefficients();
        }
 
        public float Process(float input)
        {
            double o = input * A0 + Z1;
            Z1 = input * A1 + Z2 - B1 * o;
            Z2 = input * A2 - B2 * o;
            return (float)o;
        }
 
        public void Process(float[] input)
        {
            for (int i = 0; i < input.Length; i++)
            {
                input[i] = Process(input[i]);
            }
        }
 
        protected abstract void CalculateBiQuadCoefficients();
    }
 
    public sealed class LowpassFilter : BiQuad
    {
        public LowpassFilter(int sampleRate, double frequency)
            : base(sampleRate, frequency, DefaultQ, DefaultGainDb)
        {
        }
 
        protected override void CalculateBiQuadCoefficients()
        {
            double k = Math.Tan(Math.PI * _frequency / _sampleRate);
            var norm = 1 / (1 + k / _q + k * k);
            A0 = k * k * norm;
            A1 = 2 * A0;
            A2 = A0;
            B1 = 2 * (k * k - 1) * norm;
            B2 = (1 - k / _q + k * k) * norm;
        }
    }
 
    public sealed class HighpassFilter : BiQuad
    {
        public HighpassFilter(int sampleRate, double frequency)
            : base(sampleRate, frequency, DefaultQ, DefaultGainDb)
        {
        }
 
        protected override void CalculateBiQuadCoefficients()
        {
            double k = Math.Tan(Math.PI * _frequency / _sampleRate);
            var norm = 1 / (1 + k / _q + k * k);
            A0 = 1 * norm;
            A1 = -2 * A0;
            A2 = A0;
            B1 = 2 * (k * k - 1) * norm;
            B2 = (1 - k / _q + k * k) * norm;
        }
    }
 
    public sealed class BandpassFilter : BiQuad
    {
        public BandpassFilter(int sampleRate, double frequency)
            : base(sampleRate, frequency, DefaultQ, DefaultGainDb)
        {
        }
 
        protected override void CalculateBiQuadCoefficients()
        {
            double k = Math.Tan(Math.PI * _frequency / _sampleRate);
            double norm = 1 / (1 + k / _q + k * k);
            A0 = k / _q * norm;
            A1 = 0;
            A2 = -A0;
            B1 = 2 * (k * k - 1) * norm;
            B2 = (1 - k / _q + k * k) * norm;
        }
    }
 
    public sealed class NotchFilter : BiQuad
    {
        public NotchFilter(int sampleRate, double frequency)
            : base(sampleRate, frequency, DefaultQ, DefaultGainDb)
        {
        }
 
        protected override void CalculateBiQuadCoefficients()
        {
            double k = Math.Tan(Math.PI * _frequency / _sampleRate);
            double norm = 1 / (1 + k / _q + k * k);
            A0 = (1 + k * k) * norm;
            A1 = 2 * (k * k - 1) * norm;
            A2 = A0;
            B1 = A1;
            B2 = (1 - k / _q + k * k) * norm;
        }
    }
 
    public sealed class LowShelfFilter : BiQuad
    {
        public LowShelfFilter(int sampleRate, double frequency, double gainDB)
            : base(sampleRate, frequency, DefaultQ, gainDB)
        { }
 
        protected override void CalculateBiQuadCoefficients()
        {
            const double sqrt2 = 1.4142135623730951;
            double k = Math.Tan(Math.PI * _frequency / _sampleRate);
            double v = Math.Pow(10, Math.Abs(_gainDB) / 20.0);
            double norm;
            if (_gainDB >= 0)
            {    // boost
                norm = 1 / (1 + sqrt2 * k + k * k);
                A0 = (1 + Math.Sqrt(2 * v) * k + v * k * k) * norm;
                A1 = 2 * (v * k * k - 1) * norm;
                A2 = (1 - Math.Sqrt(2 * v) * k + v * k * k) * norm;
                B1 = 2 * (k * k - 1) * norm;
                B2 = (1 - sqrt2 * k + k * k) * norm;
            }
            else
            {    // cut
                norm = 1 / (1 + Math.Sqrt(2 * v) * k + v * k * k);
                A0 = (1 + sqrt2 * k + k * k) * norm;
                A1 = 2 * (k * k - 1) * norm;
                A2 = (1 - sqrt2 * k + k * k) * norm;
                B1 = 2 * (v * k * k - 1) * norm;
                B2 = (1 - Math.Sqrt(2 * v) * k + v * k * k) * norm;
            }
        }
    }
 
    public sealed class HighShelfFilter : BiQuad
    {
        public HighShelfFilter(int sampleRate, double frequency, double gainDB)
            : base(sampleRate, frequency, DefaultQ, gainDB)
        { }
 
        protected override void CalculateBiQuadCoefficients()
        {
            const double sqrt2 = 1.4142135623730951;
            double k = Math.Tan(Math.PI * _frequency / _sampleRate);
            double v = Math.Pow(10, Math.Abs(_gainDB) / 20.0);
            double norm;
            if (_gainDB >= 0)
            {    // boost
                norm = 1 / (1 + sqrt2 * k + k * k);
                A0 = (v + Math.Sqrt(2 * v) * k + k * k) * norm;
                A1 = 2 * (k * k - v) * norm;
                A2 = (v - Math.Sqrt(2 * v) * k + k * k) * norm;
                B1 = 2 * (k * k - 1) * norm;
                B2 = (1 - sqrt2 * k + k * k) * norm;
            }
            else
            {    // cut
                norm = 1 / (v + Math.Sqrt(2 * v) * k + k * k);
                A0 = (1 + sqrt2 * k + k * k) * norm;
                A1 = 2 * (k * k - 1) * norm;
                A2 = (1 - sqrt2 * k + k * k) * norm;
                B1 = 2 * (k * k - v) * norm;
                B2 = (v - Math.Sqrt(2 * v) * k + k * k) * norm;
            }
        }
    }
 
    public sealed class PeakFilter : BiQuad
    {
        public PeakFilter(int sampleRate, double frequency, double bandWidth, double peakGainDB)
            : base(sampleRate, frequency, bandWidth, peakGainDB)
        { }
 
        protected override void CalculateBiQuadCoefficients()
        {
            double norm;
            double v = Math.Pow(10, Math.Abs(_gainDB) / 20.0);
            double k = Math.Tan(Math.PI * _frequency / _sampleRate);
            double q = _q;
 
            if (_gainDB >= 0) //boost
            {
                norm = 1 / (1 + 1 / q * k + k * k);
                A0 = (1 + v / q * k + k * k) * norm;
                A1 = 2 * (k * k - 1) * norm;
                A2 = (1 - v / q * k + k * k) * norm;
                B1 = A1;
                B2 = (1 - 1 / q * k + k * k) * norm;
            }
            else //cut
            {
                norm = 1 / (1 + v / q * k + k * k);
                A0 = (1 + 1 / q * k + k * k) * norm;
                A1 = 2 * (k * k - 1) * norm;
                A2 = (1 - 1 / q * k + k * k) * norm;
                B1 = A1;
                B2 = (1 - v / q * k + k * k) * norm;
            }
        }
    }
 
}