diff options
Diffstat (limited to 'gr-fft/include/gnuradio/fft/window.h')
| -rw-r--r-- | gr-fft/include/gnuradio/fft/window.h | 56 |
1 files changed, 41 insertions, 15 deletions
diff --git a/gr-fft/include/gnuradio/fft/window.h b/gr-fft/include/gnuradio/fft/window.h index 6739f9a0bd..8ef85d7586 100644 --- a/gr-fft/include/gnuradio/fft/window.h +++ b/gr-fft/include/gnuradio/fft/window.h @@ -22,10 +22,14 @@ namespace fft { class FFT_API window { public: + // illegal value for any window that requires a parameter + static constexpr double INVALID_WIN_PARAM = -1; + enum win_type { WIN_NONE = -1, //!< don't use a window WIN_HAMMING = 0, //!< Hamming window; max attenuation 53 dB WIN_HANN = 1, //!< Hann window; max attenuation 44 dB + WIN_HANNING = 1, //!< alias to WIN_HANN WIN_BLACKMAN = 2, //!< Blackman window; max attenuation 74 dB WIN_RECTANGULAR = 3, //!< Basic rectangular window; max attenuation 21 dB WIN_KAISER = 4, //!< Kaiser window; max attenuation see window::max_attenuation @@ -34,30 +38,52 @@ public: 5, //!< alias to WIN_BLACKMAN_hARRIS for capitalization consistency WIN_BARTLETT = 6, //!< Barlett (triangular) window; max attenuation 26 dB WIN_FLATTOP = 7, //!< flat top window; useful in FFTs; max attenuation 93 dB + WIN_NUTTALL = 8, //!< Nuttall window; max attenuation 114 dB + WIN_BLACKMAN_NUTTALL = 8, //!< Nuttall window; max attenuation 114 dB + WIN_NUTTALL_CFD = + 9, //!< Nuttall continuous-first-derivative window; max attenuation 112 dB + WIN_WELCH = 10, //!< Welch window; max attenuation 31 dB + WIN_PARZEN = 11, //!< Parzen window; max attenuation 56 dB + WIN_EXPONENTIAL = + 12, //!< Exponential window; max attenuation see window::max_attenuation + WIN_RIEMANN = 13, //!< Riemann window; max attenuation 39 dB + WIN_GAUSSIAN = + 14, //!< Gaussian window; max attenuation see window::max_attenuation + WIN_TUKEY = 15, //!< Tukey window; max attenuation see window::max_attenuation }; /*! * \brief Given a window::win_type, this tells you the maximum - * attenuation you can expect. + * attenuation (really the maximum approximation error) you can expect. * * \details - * For most windows, this is a set value. For the Kaiser window, - * the attenuation is based on the value of beta. The actual - * relationship is a piece-wise exponential relationship to - * calculate beta from the desired attenuation and can be found - * on page 542 of Oppenheim and Schafer (Discrete-Time Signal - * Processing, 3rd edition). To simplify this function to solve - * for A given beta, we use a linear form that is exact for - * attenuation >= 50 dB. + * For most windows, this is a set value. For the Kaiser, Exponential, Gaussian, and + * Tukey windows, the attenuation is based on the value of a provided parameter. + * + * For the Kaiser window the actual relationship is a piece-wise exponential + * relationship to calculate beta from the desired attenuation and can be found on + * page 542 of Oppenheim and Schafer (Discrete-Time Signal Processing, 3rd edition). + * To simplify this function to solve for A given beta, we use a linear form that is + * exact for attenuation >= 50 dB. For an attenuation of 50 dB, beta = 4.55; for an + * attenuation of 70 dB, beta = 6.76. + * + * Exponential attenuation is complicated to measure due to the irregular error ripple + * structure, but it ranges between 23 and 26 dB depending on the decay factor; 26 dB + * is a good bound. * - * For an attenuation of 50 dB, beta = 4.55. + * The Gaussian window should not be used for window based filter construction; + * instead there is a dedicated gaussian filter construction fuction. There is no + * meaningful way to measure approximation error 'delta' as shown in Fig 7.23 of + * Oppenheim and Schafer (Discrete-Time Signal Processing, 3rd edition). * - * For an attenuation of 70 dB, beta = 6.76. + * Tukey windows provide attenuation that varies non-linearily between Rectangular (21 + * dB) and Hann (44 dB) windows. * * \param type The window::win_type enumeration of the window type. - * \param beta Beta value only used for the Kaiser window. + * \param param Parameter value used for Kaiser (beta), Exponential (d), Gaussian + * (sigma) and Tukey (alpha) window creation. */ - static double max_attenuation(win_type type, double beta = 6.76); + static double max_attenuation(win_type type, double param = INVALID_WIN_PARAM); /*! * \brief Helper function to build cosine-based windows. 3-coefficient version. @@ -330,11 +356,11 @@ public: * * \param type a gr::fft::win_type index for the type of window. * \param ntaps Number of coefficients in the window. - * \param beta Used only for building Kaiser windows. + * \param param Parameter value used for Kaiser (beta), Exponential (d), Gaussian (sigma) and Tukey (alpha) window creation. * \param normalize If true, return a window with unit power */ static std::vector<float> - build(win_type type, int ntaps, double beta = 6.76, const bool normalize = false); + build(win_type type, int ntaps, double param = INVALID_WIN_PARAM, const bool normalize = false); }; } /* namespace fft */ |