common/polyphase_resampler.h

   1 #ifndef POLYPHASE_RESAMPLER_H
   2 #define POLYPHASE_RESAMPLER_H
   3
   4 #include <vector>
   5
   6 #include "alspan.h"
   7
   8
   9 using uint = unsigned int;
  10
  11 /* This is a polyphase sinc-filtered resampler. It is built for very high
  12  * quality results, rather than real-time performance.
  13  *
  14  *              Upsample                      Downsample
  15  *
  16  *              p/q = 3/2                     p/q = 3/5
  17  *
  18  *          M-+-+-+->                     M-+-+-+->
  19  *         -------------------+          ---------------------+
  20  *   p  s * f f f f|f|        |    p  s * f f f f f           |
  21  *   |  0 *   0 0 0|0|0       |    |  0 *   0 0 0 0|0|        |
  22  *   v  0 *     0 0|0|0 0     |    v  0 *     0 0 0|0|0       |
  23  *      s *       f|f|f f f   |       s *       f f|f|f f     |
  24  *      0 *        |0|0 0 0 0 |       0 *         0|0|0 0 0   |
  25  *         --------+=+--------+       0 *          |0|0 0 0 0 |
  26  *          d . d .|d|. d . d            ----------+=+--------+
  27  *                                        d . . . .|d|. . . .
  28  *          q->
  29  *                                        q-+-+-+->
  30  *
  31  *   P_f(i,j) = q i mod p + pj
  32  *   P_s(i,j) = floor(q i / p) - j
  33  *   d[i=0..N-1] = sum_{j=0}^{floor((M - 1) / p)} {
  34  *                   { f[P_f(i,j)] s[P_s(i,j)],  P_f(i,j) < M
  35  *                   { 0,                        P_f(i,j) >= M. }
  36  */
  37
  38 struct PPhaseResampler {
  39     void init(const uint srcRate, const uint dstRate);
  40     void process(const al::span<const double> in, const al::span<double> out);
  41
  42     explicit operator bool() const noexcept { return !mF.empty(); }
  43
  44 private:
  45     uint mP{}, mQ{}, mM{}, mL{};
  46     std::vector<double> mF;
  47 };
  48
  49 #endif /* POLYPHASE_RESAMPLER_H */