From b75a348e3a0f0d2493f675c4aa398cd8e6b9d1c2 Mon Sep 17 00:00:00 2001 From: Robin Gareus Date: Mon, 5 Nov 2012 22:55:13 +0000 Subject: NOOP - LTC generator: bit-alignment add comments and made permanent git-svn-id: svn://localhost/ardour2/branches/3.0@13388 d708f5d6-7413-0410-9779-e7cbd77b26cf --- libs/ardour/session_ltc.cc | 26 ++++++++++++++------------ 1 file changed, 14 insertions(+), 12 deletions(-) (limited to 'libs/ardour/session_ltc.cc') diff --git a/libs/ardour/session_ltc.cc b/libs/ardour/session_ltc.cc index 35b175e531..94d7d6de21 100644 --- a/libs/ardour/session_ltc.cc +++ b/libs/ardour/session_ltc.cc @@ -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. + * + * This is a linear approx to compensate for this drift + * and prempt re-sync when the drift builds up. * - * 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. + * 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 -- cgit v1.2.3