3 The Stretch Mode tool can be switched to by selecting it in the
4 <a href="@@toolbox">Toolbox</a>, or simply by hitting the <kbd class="menu">T</kbd>
8 It allows to extend or reduce the duration of a region, optionally maintaining
9 its pitch. This is one of the few operations in Ardour that affect the underlying
10 audio data from a region, even if the original audio is kept safely—no data
11 is lost in the process.
14 This operation is usually used to fit an audio sequence with a different rhythm
15 into a session, but can be used in a wide area of cases, due to its ability to
16 maintain or alter the pitch.
20 <img src="/images/before-stretch.png" alt="region arrangement before the stretch" />
21 <img src="/images/while-stretch.png" alt="region arrangement while stretching" />
22 <img src="/images/after-stretch.png" alt="region arrangement after the stretch" />
24 Using the Stretch Mode tool. Before stretching, while stretching, and after a stretch
29 The Stretch Mode tool is very similar in use to doing a trim in grab mode: the
30 boundary (start or end) is <kbd class="mouse">left</kbd>-clicked and dragged to
31 its wanted position. Notice a timer appearing, showing the new duration of the
32 region using the same <a href="@@editing-clocks">clock mode</a> as in the
33 <a href="@@transport-clocks">primary transport clock</a>.
36 Stretching is a complex operation (phase vocoding), involving resampling,
37 frequency analysis and synthesis. The parameters used to transform the audio
38 data are user tweakable, and exposed to the user as the <kbd class="mouse">
39 left</kbd> mouse button is released:
43 <img src="/images/time-stretch-audio.png" alt="The Time Stretch Audio window" />
45 The Time Stretch Audio window
50 The Time Stretch Audio window is made of:
54 <tr><th><dfn>Duration</dfn></th><td>The target duration of the region, expressed using the
55 primary transport clock's mode</td></tr>
56 <tr><th><dfn>Percent</dfn></th><td>The target duration of the region, expressed as a percentage
57 of the region's original length. Can be either higher than 100% (to
58 expand the region) or lower (to shrink it)</td></tr>
59 <tr><th><dfn>Contents</dfn></th><td>The type of audio the region is made of. Ardour will fine-tune
60 its algorithm based on this content, see below</td></tr>
61 <tr><th><dfn>Minimize time distortion</dfn></th><td>Tries to reduce the smearing
62 of the audio created by the phase vocoding process</td></tr>
63 <tr><th>a <dfn>Progress</dfn> bar</th><td>showing the operation in progress.</td></tr>
67 The <em>Contents</em> should be selected to best fit the actual content of the region, amongst:
70 <table style="text-align:center;">
73 <td>Disable phase resynchronisation at transients</td>
74 <td>Band-limit phase resync to extreme frequencies</td>
75 <td>Disable phase locking to peak frequencies</td>
76 <td>Use longer processing window (actual size may vary)</td>
77 <td>Use shorter processing window</td> </tr>
78 <tr><td><dfn>Mushy</dfn> </td><td>X</td><td></td><td>X</td><td>X</td><td></td></tr>
79 <tr><td><dfn>Smooth</dfn> </td><td>X</td><td></td><td>X</td><td></td><td></td></tr>
80 <tr><td><dfn>Balanced multitimbral mixture</dfn> </td><td>X</td><td></td><td></td><td></td><td></td></tr>
81 <tr><td><dfn>Unpitched percussion with stable notes</dfn> </td><td></td><td>X</td><td></td><td></td><td></td></tr>
82 <tr><td><dfn>Crisp monophonic instrumental</dfn> (<em>default</em>)</td><td></td><td></td><td></td><td></td><td></td></tr>
83 <tr><td><dfn>Unpitched solo percussion</dfn> </td><td></td><td></td><td>X</td><td></td><td>X</td></tr>
84 <tr><td><dfn>Resample without preserving pitch</dfn> </td><td colspan="5"><em>see below</em></td></tr>
89 While the table above details <em>how</em> the different kinds of audio material
90 alter the fine-tuning of the DSP, from an user point of view, the operation often
91 consists in trying different settings and listening to the result.
95 The best way to start experimenting is to consider the material itself:
99 <li>If the material doesn't need its pitch to be preserved, the best choice is
100 <em>Resample without preserving pitch</em></li>
101 <li>For drum-type material, the best choice is (depending on the transients crispness,
102 stretching factor...) one of the two <em>percussion</em> types</li>
103 <li>For melodic mono-tonal material (bass, winds,…), the best (and default) choice is <em>Crisp
104 monophonic instrumental</em></li>
105 <li>For multi-tonal material (chords,…), either one of the three first choice, or the default