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46 lines
866 B
C++
46 lines
866 B
C++
/*
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Decibel calculation helpers
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Copyright 2018 Ahmet Inan <inan@aicodix.de>
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*/
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#pragma once
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#include "exp.hh"
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namespace DSP {
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template <typename TYPE>
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TYPE decibel(TYPE v)
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{
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#if 0
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return TYPE(10) * log10(v);
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#else
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static constexpr TYPE
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// 2*1024*10/l(10)
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scale = 8894.350989378597430295120259412072085389250678859091274024013479236L,
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inv1 = TYPE(1) / TYPE(1),
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inv3 = TYPE(1) / TYPE(3),
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inv5 = TYPE(1) / TYPE(5),
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inv7 = TYPE(1) / TYPE(7),
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inv9 = TYPE(1) / TYPE(9),
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inv11 = TYPE(1) / TYPE(11),
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inv13 = TYPE(1) / TYPE(13);
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TYPE x = v;
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for (int i = 0; i < 10; ++i)
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x = sqrt(x);
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x = (x - TYPE(1)) / (x + TYPE(1));
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TYPE xx = x * x;
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return scale * x * (xx * (xx * (xx * (xx * (xx * (xx *
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inv13 + inv11) + inv9) + inv7) + inv5) + inv3) + inv1);
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#endif
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}
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template <typename TYPE>
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TYPE idecibel(TYPE dB)
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{
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return exp10(dB / TYPE(10));
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}
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}
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