231 lines
8.0 KiB
HTML
231 lines
8.0 KiB
HTML
---
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layout: default
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title: Stereo Panner
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---
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<p>
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The default stereo panner distributes 2 inputs to 2 outputs. Its
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behaviour is controlled by two parameters, width and position. The
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default settings for the stereo panner are width=100%,
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position=center (L=50%, R=50%). This panner assumes that the signals
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you wish to distribute are either uncorrelated (that means totally
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independent), or they contain a stereo image which is
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mono-compatible<sup><ahref="#caveat">*</a></sup>.
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</p>
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<div class="well">
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<p>
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With the default values it is not possible to alter the position,
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since the width is already spread entirely across both outputs. To
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alter the position, you must first reduce the width.
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</p>
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</div>
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<h2>Stereo Panner User Interface</h2>
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<img src="/images/stereo-panner-annotated.png" alt=""/>
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<p>
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The panner user interface consists of 3 elements, divided between
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the top and bottom half. Click and/or drag in the top half to
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control position; click and/or drag in the bottom half to control
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width (see below for details).
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<p>
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<p>
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In the top half is the position indicator, which shows where the
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center of the stereo image is relative to the left and right
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edges. When this is the middle of the panner, the stereo image is
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centered between the left and right outputs. When it all the way to
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the left, the stereo image collapses to just the left speaker.
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</p>
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<p>
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In the bottom half are two signal indicators, one marked "L" and the
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other "R". The distance between these two shows the width of the
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stereo image. If the width is reduced to zero, there will only be a
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single signal indicator marked "M" (for mono), and whose color will
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change to indicate the special state.
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</p>
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<p>
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It is possible to invert the outputs (see below) so that whatever
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would have gone to the right channel goes to the left and vice
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versa. When this happens, the entire movable part of the panner
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changes color to indicate clearly that this is the case.
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</p>
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<h3>Position vs. L/R</h3>
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<p>
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Although the implementation of the panner uses the "position"
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parameter, when the user interface displays it numerically, it shows a pair of numbers that
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will be familiar to most audio engineers.
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</p>
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<table>
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<tr><th>Position</th><th>L/R</th><th>English</th></tr>
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<tr><td>0</td><td>L=50% R=50%</td><td>signal image is midway between
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left and right speakers</td></tr>
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<tr><td>-1</td><td>L=100% R=0%</td><td>signal image is entirely
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at the left speaker </td></tr>
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<tr><td>1</td><td>L=0% R=100%</td><td>signal image is entirely
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at the right speaker</td></tr>
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</table>
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<p>
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One way to remember this sort of convention is that the middle of the
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USA is not Kansas, but "Los Angeles: 50% New York: 50%".
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</p>
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<h2>Examples In Use</h2>
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<table>
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<tr><th>Appearance</th><th>Settings</th></tr>
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<tr><td><img src="/images/stereo-panner.png"></td><td>Width=100%,
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L=50 R=50</td></tr>
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<tr><td><img src="/images/stereo-panner-zero.png"></td><td>Width=0%,
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L=50 R=50</td></tr>
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<tr><td><img src="/images/stereo-panner-inverted.png"></td><td>Width=-100%, Position = 0 (center)</td></tr>
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<tr><td><img src="/images/stereo-panner-right.png"></td><td>Width=36%,
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L=44 R=56</td></tr>
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<tr><td><img src="/images/stereo-panner-hard-right.png"></td><td>Width=0%,
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L=0 R=100</td></tr>
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</table>
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<h2>Using the mouse</h2>
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<p>
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Mouse operations in the upper half of the panner adjust the position
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parameter, constrained by the current width setting.
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</p>
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<p>
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Mouse operations in the lower half of the panner adjust the width
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parameter, constrained by the current position setting.
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</p>
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<p>
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To change the position smoothly, press the right button and drag
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within the top half of the panner, then release. The position will
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be limited by the current width setting. <em>Note: you do not need
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to grab the position indicator in order to drag</em>
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</p>
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<p>
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To change the width smoothly, press the right button and drag
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within the lower half of the panner, then release. The width will be
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limited by the current position setting.<em>Note: you do not need to
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grab the L/R indicators in order to drag</em>
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</p>
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<dl class="faq">
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<dt>Reset to defaults</dt>
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<dd>Click <key class="mod3">right button</key></dd>
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<dt>Change to a "hard left"</dt>
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<dd>Double click <key class="mod2">right button</key> in the upper left half
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of the panner</dd>
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<dt>Change to a "hard right"</dt>
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<dd>Double click <key class="mod2">right button</key> in the upper right half
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of the panner</dd>
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<dt>Move position as far left as possible, given width</dt>
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<dd>Double click <key>right button</key> in the upper left half of the
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panner</dd>
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<dt>Move position as far right as possible, given width</dt>
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<dd>Double click <key>right button</key> in the upper right half of the
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panner</dd>
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<dt>Set the position to center</dt>
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<dd>Click <key>right button</key> in the upper middle of the panner</dd>
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<dt>Reset to maximum possible width</dt>
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<dd>Double click <key>right button</key> on the lower left side</dd>
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<dt>Invert (flip channel assignments)</dt>
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<dd>Double click <key>right button</key> on the lower right side</dd>
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<dt>Set width to 0°</dt>
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<dd>Double click <key>right button</key> in the lower middle</dd>
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</dl>
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<h4>Keyboard bindings</h4>
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<p>
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When the pointer is within a stereo panner user interface, the following
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keybindings are available to operate on that panner:
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</p>
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<dl>
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<dt><key>↑</key> / <key class="mod1">↑</key></dt>
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<dd>increase width by 1° / 5°</dd>
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<dt><key>↓</key> / <key class="mod1">↓</key></dt>
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<dd>decrease width by 1° / 5°</dd>
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<dt><key>←</key> / <key class="mod1">←</key></dt>
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<dd>move position 1° / 5° to the left</dd>
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<dt><key>→</key> / <key class="mod1">→</key></dt>
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<dd>move position 1° / 5° to the right</dd>
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<dt><key>0</key></dt>
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<dd>reset position to center</dd>
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<dt><key class="mod2">↑</key></dt>
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<dd>reset width to full (100%)</dd>
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</dl>
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<h4>Using the scroll wheel/touch scroll</h4>
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<p>
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When the pointer is within a stereo panner user interface, the scroll
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wheel may be used as follows:
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</p>
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<dl>
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<dt>left / <key class="mod1">left</key></dt>
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<dd>increase width by 1° / 5°</dd>
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<dt>right / <key class="mod1">right</key></dt>
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<dd>decrease width by 1° / 5°</dd>
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<dt>up / <key class="mod1">up</key></dt>
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<dd>move position 1° / 5° to the left</dd>
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<dt>down / <key class="mod1">down</key></dt>
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<dd>move position 1° / 5°to the right</dd>
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</dl>
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<h2><a name="caveat" />Panning caveats</h2>
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<p>
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Note that the stereo panner will introduce unwanted side effects on
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material that includes a time difference between the channels, such
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as AB, ORTF or NOS microphone recordings, or delay-panned mixes.<br />
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With such signals, when you reduce the with, you are summing two signals
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with different delays, which will introduce comb filtering.
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</p>
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<p>
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Let's take a look at what happens when you record a source at 45° to the
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right side with an ORTF array (cardioids, spacing 17cm, opening angle
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110°):<br />
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The time difference is 350 usecs or approximately 15 samples at 44k1. The
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level difference due to the directivity of the microphones is about 7.5dB.
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</p>
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<img src="/images/stereo-panner-with-ORTF-fullwidth.png" />
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<p>
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For testing, we apply a pink noise signal, which displays as a straight line
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in the analyser. To simulate an ORTF, we use Robin Gareus' stereo balance
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control LV2 to set the level difference and time delay. Ignore the Trim/Gain
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- its purpose is just to align the test signal with the 0dB line of the
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analyser.
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</p>
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<p>
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Now for the interesting part: if we reduce the width of the signal to 50%,
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the time-delayed signals will be combined in the panner. Observe what
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happens to the frequency response:
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</p>
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<img src="/images/stereo-panner-with-ORTF-halfwidth.png" />
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<p>
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Depending on your material and on how much you need to manipulate the width,
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the comb filter may be acceptable. Then again, it may not be. Listen
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carefully for artefacts if you manipulate unknown stereo signals - many
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orchestra sample libraries for example do contain time-delay components.
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</p>
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