121 lines
6.2 KiB
HTML
121 lines
6.2 KiB
HTML
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<figure class="right">
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<img src="/images/bus-mixer-strip.png" alt="A bus mixer strip">
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</figure>
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<p>
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An Ardour bus can be considered a virtual track, as in a track that doesn't
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have a playlist (so, no regions). Its use is to "group" some audio signals to
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be treated the same way. One simple use case is to group all the audio tracks
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containing the different drums of a drumkit. Routing all the drums tracks
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outputs to a bus allows, once the different levels amongst the drums have been
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set, to adjust the global level of the drumkit in the mix.
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</p>
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<p>
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Bus usage goes way beyond this simple example though: busses, as tracks, can
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receive plugins for common audio treatment, and be routed themselves as needed.
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This makes for a very useful tool that is very commonly used both for musical
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purposes and computing ones: instead of using e.g. ten discrete delay plugins on
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ten different tracks, busses are often used as receivers of <a
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href="@@aux-sends">sends</a>, and only one delay plugin is used on this bus,
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reducing the processing power needed.
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</p>
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<h2>Audio Busses vs MIDI Busses</h3>
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<p>
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Ardour supports two types of busses: Audio and MIDI. A MIDI bus differs from an
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audio bus just by:
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<p>
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<ul>
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<li>its input (which is midi, as shown by the red signal lines in the processor box) instead of <em>n</em> audio</li>
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<li>the fact that an instrument can be placed on it at creation time, whereas it can't easily be done for an audio bus</li>
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<li>as for tracks, the MIDI bus doesn't have a trim knob or invert phase button(s).</li>
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</ul>
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<p>
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MIDI busses provide a particularly efficient workflow for virtual drumkits where
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the arrangement uses different MIDI tracks. Moreover, busses with both Audio and
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MIDI inputs are well suited for vocoders and similar plugins, where a MIDI
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signal controls an audio one.
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</p>
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<p class="note">
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Adding any audio input to a MIDI bus transforms it into an audio bus.
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</p>
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<h2>Description</h2>
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<p>
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Busses look and behave exactly like tracks, so they share nearly <a href="@@audiomidi-mixer-strips">
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all of their controls</a>. The differences are:
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</p>
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<ul>
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<li>as the busses dont have a playlist (and cannot host any media), they can't be recorded on. The recording controls are not present</li>
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<li>an <kbd class="menu">Aux</kbd> button replaces these controls.</li>
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</ul>
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<p>
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Clicking the <kbd class="menu">Aux</kbd> button makes every track that sends a
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signal to this bus through <a href="@@aux-sends">Aux sends</a> blink in
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turquoise. Right clicking this button brings up a menu:
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</p>
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<table class="dl">
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<tr><th>Assign all tracks (prefader)</th><td>Creates an Aux Send in every track, to this bus. The send is placed just before the fader</td></tr>
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<tr><th>Assign all tracks and busses (prefader)</th><td>Creates an Aux Send in every track and every bus, to this bus. The send is placed just before the fader</td></tr>
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<tr><th>Assign all tracks (postfader)</th><td>Same as above, but the send is placed just after the fader</td></tr>
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<tr><th>Assign all tracks and busses (postfader)</th><td>Same as above, with tracks and busses</td></tr>
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<tr><th>Assign selected tracks (prefader)</th><td>Same as for all tracks, but only applies to the selected tracks</td></tr>
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<tr><th>Assign selected tracks and busses (prefader)</th><td>Same as for all tracks and busses, but only applies to the selected tracks and busses</td></tr>
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<tr><th>Assign selected tracks (postfader)</th><td>Same as above, but the send is placed just after the fader</td></tr>
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<tr><th>Assign selected tracks and busses (postfader)</th><td>Same as above, with tracks and busses</td></tr>
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<tr><th>Set sends gain to -inf</th><td>For all the sends to this bus, put the send fader to −∞ so no signal is sent</td></tr>
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<tr><th>Set sends gain to 0dB</th><td>For all the sends to this bus, put the send fader at the default position, 0dB (100% of th signal is sent)</td></tr>
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</table>
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<h2>Connecting a track to a bus</h2>
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<p>
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Depending on the user's workflow and the way busses are used, two possibilities exists:
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</p>
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<h3>Connecting a track to a bus via its outputs</h3>
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<img class="left" src="/images/connecting_bus_output.png" alt="Connecting a bus through a track's outputs">
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<p>
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Connecting the output(s) of a track to the input(s) of the bus sends
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<em>all</em> the audio/MIDI to the bus. In the mixer strip, select (at the
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bottom) the OUTPUT button (often, by default, "Master"), and in the list,
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choose the input of a bus. Note that only the bus able to receive this output
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will show up, e.g. a mono bus won't be able to be connected to the output of a
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stereo track).
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</p>
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<p>
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Obviously, doing so will (by default) disconnect the output from the Master's
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input, which means all the audio/MIDI will be routed to the bus. For more
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complex routing, the OUTPUT button allows to show the <kbd class="menu">Routing
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Grid</kbd> that allows to plug the output of the track to multiple outputs at
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once, be it busses, tracks, Master… The button will then reflect these
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multiple connections by showing a <em>*number*</em>, number being the number of
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connections made in the routing grid.
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</p>
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<h3>Connecting a track to a bus via Sends</h3>
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<img class="left" src="/images/connecting_bus_send.png" alt="Connecting a bus through a send">
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<p>
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This allows not to interrupt the natural flow of the signal, i.e. the track will
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still output to what its connected to (e.g. Master). The signal is "tapped" at
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the point of insertion of the send, to be sent to the bus, by <kbd class="mouse">right</kbd>
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clicking where in the signal flow the signal should be tapped, and selecting <kdb class="menu">
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New Aux Send… > name_of_the_bus</kbd>.
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</p>
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<p>
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By <kbd class="mouse">left-clicking</kbd> the send meter, it is possible to
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adjust the amount of signal sent to the bus. This is often the way tracks are
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connected to an effect bus, like a Delay bus.
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</p>
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<p class="note">
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Busses can be plugged to other busses, through outputs or sends. Both example
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workflows discussed previously, i.e. busses for grouping tracks and busses for
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effects, can both coexist, as e.g. a "grouping" drum bus can have a send to a
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reverb bus, and be connected to a compressor bus.
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</p>
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