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NOOP - LTC generator: bit-alignment add comments and made permanent

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git-svn-id: svn://localhost/ardour2/branches/3.0@13388 d708f5d6-7413-0410-9779-e7cbd77b26cf
This commit is contained in:
Robin Gareus 2012-11-05 22:55:13 +00:00
parent 6035b92036
commit b75a348e3a
1 changed files with 14 additions and 12 deletions
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26
libs/ardour/session_ltc.cc
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@ -479,24 +479,26 @@ 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 =
/* reduce (low freq) jitter.
* The granularity of the LTC encoder speed is 1 byte =
* (frames-per-timecode-frame / 10) audio-samples.
* Thus, tiny speed changes [as produced by the slave]
* may not have any effect in the cycle when they occur,
* but they will add up over time.
*
* 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.
* This is a linear approx to compensate for this drift
* and prempt re-sync when the drift builds up.
*
* However, for very fast speeds - when 1 LTC bit is
* <= 3 audio-sample - adjusting speed may lead to
* invalid frames.
*
* To do better than this, 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