common/polyphase_resampler.h

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