108 lines
4.9 KiB
HTML
108 lines
4.9 KiB
HTML
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<p>
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The Stretch Mode tool can be switched to by selecting it in the
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<a href="@@toolbox">Toolbox</a>, or simply by hitting the <kbd class="menu">T</kbd>
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key.
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</p>
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<p>
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It allows to extend or reduce the duration of a region, optionnaly maintaining
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its pitch. This is one of the few operations in Ardour that affect the underlying
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audio data from a region, even if the original audio is kept safely—no data
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is lost in the process.
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</p>
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<p>
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This operation is usually used to fit an audio sequence with a different rhythm
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into a session, but can be used in a wide area of cases, due to its ability to
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maitain or alter the pitch.
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</p>
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<figure>
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<img src="/images/before-stretch.png" alt="region arrangement before the stretch" />
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<img src="/images/while-stretch.png" alt="region arrangement while stretching" />
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<img src="/images/after-stretch.png" alt="region arrangement after the stretch" />
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<figcaption>
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Using the Stretch Mode tool. Before stretching, while stretching, and after a stretch
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</figcaption>
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</figure>
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<p>
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The Stretch Mode tool is very similar in use to doing a trim in grab mode: the
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boundary (start or end) is <kbd class="mouse">left</kbd>-clicked and dragged to
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its wanted position. Notice a timer appearing, showing the new duration of the
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region using the same <a href="@@editing-clocks">clock mode</a> as in the
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<a href="@@transport-clocks">primary transport clock</a>.
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</p>
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<p>
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Stretching is a complex operation (phase vocoding), involving resampling,
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frequency analysis and synthesis. The parameters used to transform the audio
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data are user tweakable, and exposed to the user as the <kbd class="mouse">
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left</kbd> mouse button is released:
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</p>
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<figure>
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<img src="/images/time-stretch-audio.png" alt="The Time Stretch Audio window" />
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<figcaption>
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The Time Stretch Audio window
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</figcaption>
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</figure>
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<p>
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The Time Stretch Audio window is made of:
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</p>
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<dl>
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<dt><dfn>Duration</dfn></dt><dd>The target duration of the region, expressed using the
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primary transport clock's mode</dd>
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<dt><dfn>Percent</dfn></dt><dd>The target duration of the region, expressed as a percentage
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of the region's original lenght. Can be either higher than 100% (to
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expand the region) or lower (to shrink it)</dd>
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<dt><dfn>Contents</dfn></dt><dd>The type of audio the region is made of. Ardour will fine-tune
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its algorithm based on this content, see below</dd>
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<dt><dfn>Minimize time distortion</dfn></dt><dd>Tries to reduce the smearing
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of the audio created by the pahse vocoding process</dd>
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<dt>a <dfn>Progress</dfn> bar</dt><dd>showing the operation in progress.</dd>
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</dl>
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<p>
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The <em>Contents</em> should be selected to best fit the actual content of the region, amongst:
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</p>
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<table class="alternate" style="text-align:center;">
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<tbody>
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<tr> <td>Content</td>
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<td>Disable phase resynchronisation at transients</td>
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<td>Band-limit phase resync to extreme frequencies</td>
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<td>Disable phase locking to peak frequencies</td>
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<td>Use longer processing window (actual size may vary)</td>
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<td>Use shorter processing window</td> </tr>
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<tr><td><dfn>Mushy</dfn> </td><td>X</td><td></td><td>X</td><td>X</td><td></td></tr>
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<tr><td><dfn>Smooth</dfn> </td><td>X</td><td></td><td>X</td><td></td><td></td></tr>
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<tr><td><dfn>Balanced multitimbral mixture</dfn> </td><td>X</td><td></td><td></td><td></td><td></td></tr>
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<tr><td><dfn>Unpitched percussion with stable notes</dfn> </td><td></td><td>X</td><td></td><td></td><td></td></tr>
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<tr><td><dfn>Crisp monophonic instrumental</dfn> (<em>default</em>)</td><td></td><td></td><td></td><td></td><td></td></tr>
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<tr><td><dfn>Unpitched solo percussion</dfn> </td><td></td><td></td><td>X</td><td></td><td>X</td></tr>
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<tr><td><dfn>Resample without preserving pitch</dfn> </td><td colspan="5"><em>see below</em></td></tr>
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</tbody>
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</table>
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<p>
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While the table above details <em>how</em> the different kinds of audio material
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alter the fine-tuning of the DSP, from an user point of view, the operation often
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consists in trying different settings and listening to the result.
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</p>
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<p>
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The best way to start experimenting is to consider the material itself:
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</p>
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<ul>
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<li>If the material doesn't need its pitch to be preserved, the best choice is
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<em>Resample without preserving pitch</em></li>
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<li>For drum-type material, the best choice is (depending on the transients crispness,
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stretching factor...) one of the two <em>percussion</em> types</li>
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<li>For melodic mono-tonal material (bass, winds,…), the best (and default) choice is <em>Crisp
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monophonic instrumental</em></li>
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<li>For multi-tonal material (chords,…), either one of the three first choice, or the default
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<em>Crisp</em>.</li>
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</ul>
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