computeWindow()

static void fl::audio::fft::Context::computeWindow ( fl::vector< alpha16 > & win, int N, Window type )

inlinestaticprivate

Definition at line 501 of file fft_impl.cpp.hpp.

                                                                                       {
        using FP = fl::fixed_point<16, 16>;
        win.resize(N);
 
        // NONE: rectangular window (all coefficients = 1.0)
        if (type == Window::NONE) {
            for (int n = 0; n < N; ++n) {
                win[n] = alpha16(65535);
            }
            return;
        }
 
        const FP two_pi(6.2831853f);   // 2π
        const FP invNm1 = FP(1) / FP(N - 1);
        const FP phase_step = two_pi * invNm1;
 
        // Blackman-Harris coefficients
        constexpr FP bh_a0(0.35875f);
        constexpr FP bh_a1(0.48829f);
        constexpr FP bh_a2(0.14128f);
        constexpr FP bh_a3(0.01168f);
        // Hanning coefficients
        constexpr FP half(0.5f);
        constexpr FP one(1.0f);
 
        FP phase(0.0f);
        for (int n = 0; n < N; ++n) {
            FP w;
            switch (type) {
            case Window::BLACKMAN_HARRIS: {
                // 4-term Blackman-Harris: -92 dB sidelobe rejection
                FP phase2 = phase + phase;
                FP phase3 = phase2 + phase;
                w = bh_a0 - bh_a1 * FP::cos(phase)
                    + bh_a2 * FP::cos(phase2)
                    - bh_a3 * FP::cos(phase3);
                break;
            }
            case Window::HANNING:
            default:
                w = half * (one - FP::cos(phase));
                break;
            }
            i32 raw = w.raw();
            if (raw < 0) raw = 0;          // guard against FP rounding
            if (raw > 65535) raw = 65535;   // 1.0 in s16x16 = 65536, clamp for u16
            win[n] = alpha16(static_cast<unsigned short>(raw));
            phase = phase + phase_step;
        }
    }

References fl::audio::fft::BLACKMAN_HARRIS, fl::FL_NO_EXCEPT, fl::audio::fft::HANNING, fl::audio::fft::NONE, and fl::s16x16::raw().

Referenced by initHybrid(), initLogRebin(), initOctaveWise(), and initWindow().

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