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experimental LTC sub-frame drift compensation for scope testing

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git-svn-id: svn://localhost/ardour2/branches/3.0@13384 d708f5d6-7413-0410-9779-e7cbd77b26cf
This commit is contained in:
Robin Gareus 2012-11-05 19:13:10 +00:00
parent fb630f622d
commit 0a4f4026a9
1 changed files with 30 additions and 2 deletions
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32
libs/ardour/session_ltc.cc
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@ -50,9 +50,13 @@ using namespace Timecode;
* yet with most sound-cards a square-wave of 1-2 sample
* introduces rather some ringing and small oscillations.
* so we low-pass filter the signal a bit, depending
* on the sample-rate
* on the sample-rate.
*
* TODO: this should become an adaptive value, when
* the playback speed is increases so that 1 bit < 3-4
* audio samples, we should fall back to 25 us.
*/
#define LTC_RISE_TIME MIN (150, MAX(25, (4000000 / engine().frame_rate())))
#define LTC_RISE_TIME MIN (100, MAX(25, (2000000 / engine().frame_rate())))
void
Session::ltc_tx_initialize()
@ -465,6 +469,24 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX5 restart @ %1 + %2 - %3 | byte %4\n",
ltc_enc_pos, ltc_enc_cnt, cyc_off, ltc_enc_byte));
}
#if 1 /* experimental sample bit alignment */
else if (ltc_speed != 0 && (fptcf / ltc_speed / 80) > 3 ) {
/* We may get away without a DLL if speed-changes are uniform enough and
* no oscillation takes place, the linear approx here should reduce the
* jitter sufficiently when generating LTC from another LTC source or
* JACK-transport or ardour internal clock.
*
* Note that the granularity of the LTC encoder speed is 1 byte =
* (frames-per-timecode-frame / 10) audio-samples.
*
* Thus, tiny speed changes won't have any effect and larger ones
* may lead to oscillations.
* To be better than that, resampling (or a rewrite of the encoder) is
* required.
*/
ltc_speed -= ((ltc_enc_pos + ltc_enc_cnt - poff) - cycle_start_frame) / engine().frame_rate();
}
#endif
// (6) encode and output
@ -529,6 +551,12 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
ltc_enc_byte = (ltc_enc_byte + 1)%10;
if (ltc_enc_byte == 0 && ltc_speed != 0) {
ltc_encoder_inc_timecode(ltc_encoder);
#if 0 /* force fixed parity -- scope debug */
LTCFrame f;
ltc_encoder_get_frame(ltc_encoder, &f);
f.biphase_mark_phase_correction=0;
ltc_encoder_set_frame(ltc_encoder, &f);
#endif
ltc_tx_recalculate_position();
ltc_enc_cnt = 0;
} else if (ltc_enc_byte == 0) {