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LTC generator: adaptive signal filter

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git-svn-id: svn://localhost/ardour2/branches/3.0@13386 d708f5d6-7413-0410-9779-e7cbd77b26cf
This commit is contained in:
Robin Gareus 2012-11-05 22:55:04 +00:00
parent 0a4f4026a9
commit 3f1b758491
1 changed files with 10 additions and 11 deletions
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21
libs/ardour/session_ltc.cc
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@ -48,15 +48,15 @@ using namespace Timecode;
/* LTC signal should have a rise time of 25 us +/- 5 us.
* 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.
* introduces ringing and small oscillations.
* https://en.wikipedia.org/wiki/Gibbs_phenomenon
* A low-pass filter in libltc can reduce this at
* the cost of being slightly out of spec WRT to rise-time.
*
* 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.
* This filter is adaptive so that fast vari-speed signals
* will not be affected by it.
*/
#define LTC_RISE_TIME MIN (100, MAX(25, (2000000 / engine().frame_rate())))
#define LTC_RISE_TIME(speed) MIN (100, MAX(25, (4000000 / ((speed==0)?1:speed) / engine().frame_rate())))
void
Session::ltc_tx_initialize()
@ -69,7 +69,7 @@ Session::ltc_tx_initialize()
0);
ltc_encoder_set_bufsize(ltc_encoder, nominal_frame_rate(), 23.0);
ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME);
ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(1.0));
/* buffersize for 1 LTC frame: (1 + sample-rate / fps) bytes
* usually returned by ltc_encoder_get_buffersize(encoder)
@ -198,9 +198,7 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
ltc_tx_cleanup();
return;
}
if (nominal_frame_rate() <= 48000) {
ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME);
}
ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(ltc_speed));
ltc_enc_tcformat = cur_timecode;
ltc_tx_reset();
}
@ -246,6 +244,7 @@ Session::ltc_tx_send_time_code_for_cycle (framepos_t start_frame, framepos_t end
*/
DEBUG_TRACE (DEBUG::LTC, string_compose("LTC TX2: speed change old: %1 cur: %2 tgt: %3 ctd: %4\n", ltc_speed, current_speed, target_speed, fabs(current_speed) - target_speed));
speed_changed = true;
ltc_encoder_set_filter(ltc_encoder, LTC_RISE_TIME(new_ltc_speed));
}
if (end_frame == start_frame || fabs(current_speed) < 0.1 ) {