+++ /dev/null
----
-layout: default
-title: Timecode Generators and Slaves
----
-
-<p>
- Ardour supports three common timecode formats:
- <abbr title="Linear/Longitudinal Time Code"><dfn>LTC</dfn></abbr>,
- <abbr title="MIDI Time Code"><dfn>MTC</dfn></abbr>, and
- <dfn>MIDI Clock</dfn>, as well as
- <dfn>JACK-transport</dfn>, a JACK-specific timecode implementation.
-</p>
-
-<p>
- Ardour can generate timecode and thus act as timecode <dfn>master</dfn>,
- providing timecode information to other applications. Ardour can also be
- <dfn>slaved</dfn> to some external source in which case the playhead
- follows the incoming timecode.
-</p>
-
-<p>
- Combining the timecode slave and generator modes, Ardour can also
- <dfn>translate</dfn> timecode. e.g create LTC timecode from incoming MTC.
-</p>
-
-<h2>Ardour Timecode Configuration</h2>
-
-<p>
- Each Ardour session has a specific timecode frames-per-second setting which
- is configured in <kbd class="menu">session > properties >
- timecode</kbd>. The selected timecode affects the timecoderuler in the main
- window as well as the clock itself.
-</p>
-
-<p>
- Note that some timecode formats do not support all of Ardour's available
- fps settings. MTC is limited to 24, 25, 29.97 and 30 fps.
-</p>
-
-<p>
- The video pull-up modes change the effective samplerate of Ardour to allow
- for changing a film soundtrack from one frame rate to another. The concept is
- beyond the scope of this manual, but Wikipedia's entry on
- <a href="http://en.wikipedia.org/wiki/Telecine">Telecine</a>
- may get you started.
-</p>
-
-<h2>Ardour Timecode Generator Configuration</h2>
-
-<p>
- This is pretty straightforward: simply turn it on. The MTC and MIDI-Clock
- generator do not have any options. The LTC generator has a configurable
- output level. JACK-transport cannot be <em>generated</em>. Jack itself is
- always synced to its own cycle and cannot do varispeed—it will
- always be synced to a hardware clock or another JACK master.
-</p>
-
-<p>
- The relevant settings for timecode generator can be found in
- <kbd class="menu">Edit > Preferences > MIDI Preferences</kbd> (for MTC,
- MC) and
- <kbd class="menu">Edit > Preferences > Transport Preferences</kbd>
- (for LTC).
-</p>
-
-<p>
- The timecode is sent to jack-ports <code>ardour:MTC out</code>,
- <code>ardour:MIDI clock out</code> and <code>ardour:LTC-out</code>. Multiple
- generators can be active simultaneously.
-</p>
-
-<p class="note">
- Note that, as of Jan 2014, only the LTC generator supports latency
- compensation. This is due to the fact the Ardour MIDI ports are not
- yet latency compensated.
-</p>
-
-<p>
- In <kbd class="menu">Session > Properties</kbd>, it is possible to
- define an offset between Ardour's internal time and the timecode sent.
- Currently only the LTC generator honors this offset.
-</p>
-
-<p>
- Both LTC and MTC are limited to 30 fps. Using frame rates larger
- than that will disable the generator. In both cases also only 24, 25,
- 29.97df (drop-frame) and 30 fps are well defined by specifications (such as
- SMPTE-12M, EU and the MIDI standard).
-</p>
-
-<h3>MTC Generator</h3>
-
-<p>
- The <dfn>MTC generator</dfn> has no options. Ardour sends full MTC
- frames whenever the transport is relocated or changes state (start/stop).
- MTC <dfn>quarter frames</dfn> are sent when the transport is rolling and
- the transport speed is within 93% and 107%.
-</p>
-
-<h3>LTC Generator</h3>
-
-<p>
- The level of the <dfn>LTC generator</dfn> output signal can be configured
- in in the <kbd class="menu">Preferences > Transport</kbd> dialog. By
- default it is set to -18 dBFS, which corresponds to 0dBu in an EBU
- calibrated system.
-</p>
-
-<p>
- The LTC generator has an additional option to keep sending timecode even
- when the transport is stopped. This mode is intended to drive analog tape
- machines which unspool the tape if no LTC timecode is received.
-</p>
-
-<p>
- LTC is send regardless of Ardour's transport speed. It is accurately
- generated even for very slow speeds (<5%) and only limited by the
- soundcard's sampling-rate and filter (see
- <a
- href="http://en.wikipedia.org/wiki/Gibbs_phenomenon#Signal_processing_explanation">Gibbs phenomenon</a>)
- for high speeds.
-</p>
-
-<h2>Ardour Slave Configuration</h2>
-
-<p>
- The timecode source can be switched with the button just right of
- Ardour's main clock. By default it is set to <kbd
- class="menu">Internal</kbd> in which case Ardour will ignore any external
- timecode. The button allows to toggle between Internal and the configured
- timecode source which is chosen in <kbd class="menu">Edit > Preferences
- > Transport</kbd>.
-</p>
-
-<p>
- When Ardour is <dfn>chasing</dfn> (synchronizing to) an external timecode
- source, the following cases need to be distinguished:
-</p>
-
-<ol>
- <li>the timecode source shares the clock</li>
- <li>the timecode source is independent (no wordclock sync)</li>
-</ol>
-
-<p>and</p>
-
-<ol>
- <li>the timecode source uses the same FPS setting as Ardour</li>
- <li>the timecode source runs at different frames-per-second</li>
-</ol>
-
-<p>
- In both cases the first option is preferred: clock sync + same FPS setting.
-</p>
-
-<h3>Frames-per-second</h3>
-
-<p>
- If the frames-per-second do not match, Ardour can either re-calculate
- and map the frames, or the configured FPS (<kbd class="menu">Session >
- Properties</kbd>) can be changed automatically while the slave is active.
- The behavior is configured with the checkbox <kbd class="option">Edit
- > Preferences > Transport > Match session video frame rate to
- external timecode</kbd>.
-</p>
-
-<p>
- When enabled, the session video frame rate will be changed to match that
- of the selected external timecode source. When disabled, the session video
- frame rate will not be changed to match that of the selected external
- timecode source. Instead the frame rate indication in the main clock will
- flash red, and Ardour will convert between the external timecode standard
- and the session standard.
-</p>
-
-<p class="warning">
- 29.97 drop-frame timecode is another corner case. While the SMPTE 12M-1999
- specifies 29.97df as 30000/1001 frames per second, not all hardware devices
- follow that standard. The checkbox
- <kbd class="option">Lock to 29.9700 fps instead of 30000/1001</kbd> allows
- to use a compatibility mode for those devices.
-</p>
-
-<p>
- When enabled, the external timecode source is assumed to use 29.970000 fps
- instead of 30000/1001. SMPTE 12M-1999 specifies 29.97df as 30000/1001. The
- <abbr title="specification">spec</abbr> further mentions that drop-frame
- timecode has an accumulated error of -86 ms over a 24-hour period.
- Drop-frame timecode would compensate exactly for a NTSC color frame rate
- of 30 * 0.9990 (ie 29.970000). That is <em>not</em> the actual rate. However,
- some vendors use that rate—despite it being against the specs—because the variant of using exactly 29.97 fps yields zero timecode
- drift.
-</p>
-
-<h3>Clock Sync Lock</h3>
-
-<p>
- As described in the
- <a href="http://manual.ardour.org/synchronization/on-clock-and-time/">On Clock and Time</a>
- chapter, timecode and clock are independent. If the external timecode
- source is not in sample-sync with the audio hardware (and JACK), Ardour
- needs to run at varispeed to adjust for the discrepancy.
-</p>
-
-<p>
- The checkbox <kbd class="option">External timecode is sync locked</kbd>
- allows to select the behavior according to your setup. When enabled, it
- indicates that the selected external timecode source shares sync (Black
- & Burst, Wordclock, etc) with the audio interface.
-</p>
-
-<p>
- In other words: if enabled, Ardour will only perform initial
- synchronization and keep playing at speed 1.0 instead of vari-speed
- adjusting to compensate for drift.
-</p>
-
-<p class="note">
- Note that vari-speed is unavailable when recording in Ardour, and all
- tracking happens at speed 1.0. So if you want to record in sync with
- external timecode it must be sample-locked or it will drift over time.
-</p>
-
-<h3>MIDI Clock</h3>
-
-<p>
- <dfn>MIDI Clock</dfn> is not a timecode format but tempo-based time. The
- absolute reference point is expressed as beats-per-minute and Bar, Beat
- and Tick. There is no concept of sample-locking for MIDI clock signals.
- Ardour will vari-speed if necessary to chase the incoming signal.
-</p>
-
-<p>
- Note that the MIDI Clock source must be connected to the
- <code>ardour:MIDI clock in</code> port.
-</p>
-
-<h3>LTC - Linear Timecode</h3>
-
-<p>
- The <dfn>LTC</dfn> slave decodes an incoming LTC signal on a JACK audio
- port. It will auto-detect the frame rate and start locking to the signal
- once two consecutive LTC frames have been received.
-</p>
-
-<p>
- The incoming timecode signal needs to arrive at the
- <code>ardour:LTC-in</code> port. Port-connections are restored for each
- session and the preference dialog offers an option to select it for all
- sessions.
-</p>
-
-<p>
- Ardour's transport is aligned to LTC-frame start/end positions according
- to the SMPTE 12M-1999 specification, which means that the first bit of an
- LTC-Frame is aligned to different Lines of a Video-Frame, depending on the
- TV standard used. Only for Film (24fps) does the LTC-Frame directly match
- the video Frame boundaries.
-</p>
-
-<img src="/images/ltc-transport-alignment.png" title="LTC frame alignment" alt="LTC frame alignment"/>
-<p><em>Figure: LTC frame alignment for the 525/60 TV standard</em></p>
-
-<p>
- Ardour supports vari-speed and backwards playback but will only follow
- speed changes if the <kbd class="optoff">sync locked</kbd> option is
- disabled.
-</p>
-
-<p>
- While Ardour is chasing LTC, the main transport clock will display the
- received Timecode as well as the delta between the incoming signal and
- Ardour's transport position.
-</p>
-
-<p>
- A global offset between incoming timecode and Ardour's transport can be
- configured in <kbd class="menu">Session > Properties</kbd>.
-</p>
-
-<p>
- The user-bits in the received LTC frame are ignored.
-</p>
-
-<h3>MTC - MIDI Timecode</h3>
-
-<p>
- Ardour's MTC slave parses <dfn>full timecode messages</dfn> as well as
- MTC <dfn>quarter-frame messages</dfn> arriving on the
- <code>ardour:MTC in</code> port. The transport will only start rolling
- once a complete sequence of 8 quarter frames has been received.
-</p>
-
-<p>
- Ardour supports vari-speed and backwards playback but will only follow
- MTC speed changes if the <kbd class="optoff">sync locked</kbd> option
- is disabled.
-</p>
-
-<p>
- When Ardour is chasing MTC, the main transport clock will display the
- received Timecode as well as the delta between the incoming signal and
- Ardour's transport position.
-</p>
-
-<h3>JACK Transport</h3>
-
-<p>
- When slaved to jack, Ardour's transport will be identical to
- JACK-transport. As opposed to other slaves, Ardour can be used to control
- the JACK transport states (stopped/rolling). No port connections need to
- be made for jack-transport to work.
-</p>
-
-<p>
- JACK-transport does not support vari-speed, nor offsets. Ardour does not
- chase the timecode but is always in perfect sample-sync with it.
-</p>
-
-<p>
- JACK-transport also includes temp-based-time information in Bar:Beats:Ticks
- and beats-per-minute. However, only one JACK application can provide this
- information at a given time. The checkbox
- <kbd class="option">Session > Properties > JACK Time Master</kbd>
- configures Ardour to act as translator from timecode to BBT information.
-</p>
-
projects / ardour-manual-diverged / blobdiff