ardour/livetrax
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* add comments / improve readability of varispeed playback code

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git-svn-id: svn://localhost/ardour2/branches/3.0@4395 d708f5d6-7413-0410-9779-e7cbd77b26cf
This commit is contained in:
Hans Baier 2009-01-09 09:54:38 +00:00
parent 799b6ec97d
commit 3d2c1ba3e6
1 changed files with 10 additions and 2 deletions
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12
libs/ardour/audio_diskstream.cc
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@ -780,6 +780,11 @@ AudioDiskstream::process (nframes_t transport_frame, nframes_t nframes, nframes_
if (rec_nframes == 0 && _actual_speed != 1.0f && _actual_speed != -1.0f) {
// 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;
int64_t phi_delta;
nframes_t i = 0;
@ -794,6 +799,9 @@ AudioDiskstream::process (nframes_t transport_frame, nframes_t nframes, nframes_
// The advantage is that addition and modulus [like x = (x + y) % 2^40]
// has no rounding errors and no drift, and just requires a single integer add.
// (swh)
const int64_t fractional_part_mask = 0xFFFFFF;
const Sample binary_scaling_factor = 16777216.0f;
// phi = fixed point speed
if (phi != target_phi) {
@ -812,7 +820,7 @@ AudioDiskstream::process (nframes_t transport_frame, nframes_t nframes, nframes_
for (nframes_t outsample = 0; outsample < nframes; ++outsample) {
i = phase >> 24;
fractional_part = (phase & 0xFFFFFF) / 16777216.0f;
fractional_part = (phase & fractional_part_mask) / binary_scaling_factor;
chaninfo->speed_buffer[outsample] =
chaninfo->current_playback_buffer[i] * (1.0f - fractional_part) +
chaninfo->current_playback_buffer[i+1] * fractional_part;
@ -823,7 +831,7 @@ AudioDiskstream::process (nframes_t transport_frame, nframes_t nframes, nframes_
}
playback_distance = i; // + 1;
last_phase = (phase & 0xFFFFFF);
last_phase = (phase & fractional_part_mask);
} else {
playback_distance = nframes;