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author | Hans Baier <hansfbaier@googlemail.com> | 2009-06-10 00:03:28 +0000 |
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committer | Hans Baier <hansfbaier@googlemail.com> | 2009-06-10 00:03:28 +0000 |
commit | f284d28d5306114e9badc9077835683e541420e0 (patch) | |
tree | 500bbe83900479c1a0780e780242187cd51bc9ef /libs/ardour/interpolation.cc | |
parent | d039e2e80ff2179aef7430c53ca41e43297d9065 (diff) |
libardour: * Add basic classes for later support of multiple interpolation algorithms for varispeed
* Add unit tests: Test which shows how the varispeed implementation in diskstream is broken.
git-svn-id: svn://localhost/ardour2/branches/3.0@5144 d708f5d6-7413-0410-9779-e7cbd77b26cf
Diffstat (limited to 'libs/ardour/interpolation.cc')
-rw-r--r-- | libs/ardour/interpolation.cc | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/libs/ardour/interpolation.cc b/libs/ardour/interpolation.cc new file mode 100644 index 0000000000..7aece6453c --- /dev/null +++ b/libs/ardour/interpolation.cc @@ -0,0 +1,43 @@ +#include <stdint.h> +#include "ardour/interpolation.h" + +nframes_t +LinearInterpolation::interpolate (nframes_t nframes, Sample *input, Sample *output) +{ + // the idea behind phase is that when the speed is not 1.0, we have to + // interpolate between samples and then we have to store where we thought we were. + // rather than being at sample N or N+1, we were at N+0.8792922 + // so the "phase" element, if you want to think about this way, + // varies from 0 to 1, representing the "offset" between samples + uint64_t phase = last_phase; + + // acceleration + int64_t phi_delta; + + // phi = fixed point speed + if (phi != target_phi) { + phi_delta = ((int64_t)(target_phi - phi)) / nframes; + } else { + phi_delta = 0; + } + + // index in the input buffers + nframes_t i = 0; + + for (nframes_t outsample = 0; outsample < nframes; ++outsample) { + i = phase >> 24; + Sample fractional_phase_part = (phase & fractional_part_mask) / binary_scaling_factor; + + // Linearly interpolate into the output buffer + // using fixed point math + output[outsample] = + input[i] * (1.0f - fractional_phase_part) + + input[i+1] * fractional_phase_part; + phase += phi + phi_delta; + } + + last_phase = (phase & fractional_part_mask); + + // playback distance + return i; +} |