diff options
| author | Robin Gareus <robin@gareus.org> | 2012-11-05 22:55:04 +0000 |
|---|---|---|
| committer | Robin Gareus <robin@gareus.org> | 2012-11-05 22:55:04 +0000 |
| commit | 3f1b758491b59c3d06ef1b4c3577fb2eba8d16f0 (patch) | |
| tree | 76f1f6df1ae25368edc0c281e57240490951f766 /libs/ardour/session_ltc.cc | |
| parent | 0a4f4026a9e98ad2466d7f3e7de41dac8f22a136 (diff) | |
LTC generator: adaptive signal filter
git-svn-id: svn://localhost/ardour2/branches/3.0@13386 d708f5d6-7413-0410-9779-e7cbd77b26cf
Diffstat (limited to 'libs/ardour/session_ltc.cc')
| -rw-r--r-- | libs/ardour/session_ltc.cc | 21 |
1 files changed, 10 insertions, 11 deletions
diff --git a/libs/ardour/session_ltc.cc b/libs/ardour/session_ltc.cc index 8d976ea4da..516daea76d 100644 --- a/libs/ardour/session_ltc.cc +++ b/libs/ardour/session_ltc.cc @@ -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 ) { |