+++ /dev/null
----
-layout: default
-title: Stereo Panner
----
-
-<p>
- The default <dfn>stereo panner</dfn> distributes two inputs to two outputs. Its
- behaviour is controlled by two parameters, <dfn>width</dfn> and
- <dfn>position</dfn>. By default, the panner is centered at full width.
-</p>
-<p>
- The stereo panner assumes that the signals
- you wish to distribute are either uncorrelated (i.e. totally
- independent), or that they contain a stereo image which is
- <dfn>mono-compatible</dfn>, such as a co-incident microphone recording, or a
- sound stage that has been created with pan pots.<sup><a href="#caveat">*</a></sup>
-</p>
-<p class="note">
- With the default values it is not possible to alter the position,
- since the width is already spread entirely across both outputs. To
- alter the position, you must first reduce the width.
-</p>
-
-<h2>Stereo Panner User Interface</h2>
-
-<img src="/images/stereo-panner-annotated.png" alt=""/>
-<p>
- The <dfn>panner user interface</dfn> consists of three elements, divided between
- the top and bottom half. Click and/or drag in the top half to
- control position; click and/or drag in the bottom half to control
- width (see below for details).
-</p>
-<p>
- In the top half is the position indicator, which shows where the
- center of the stereo image is relative to the left and right
- edges. When this is the middle of the panner, the stereo image is
- centered between the left and right outputs. When it all the way to
- the left, the stereo image collapses to just the left speaker.
-</p>
-<p>
- In the bottom half are two signal indicators, one marked "L" and the
- other "R". The distance between these two shows the width of the
- stereo image. If the width is reduced to zero, there will only be a
- single signal indicator marked "M" (for mono), whose color will
- change to indicate the special state.
-</p>
-<p>
- It is possible to invert the outputs (see below) so that whatever
- would have gone to the right channel goes to the left and vice
- versa. When this happens, the entire movable part of the panner
- changes color to indicate clearly that this is the case.
-</p>
-
-<h3>Position vs. L/R</h3>
-
-<p>
- Although the implementation of the panner uses the "position"
- parameter, when the user interface displays it numerically, it shows
- a pair of numbers that will be familiar to most audio engineers.
-</p>
-
-<table>
-<tr><th>Position</th><th>L/R</th><th>English</th></tr>
-<tr><td>0</td><td>L=50% R=50%</td><td>signal image is midway between
- left and right speakers</td></tr>
-
-<tr><td>-1</td><td>L=100% R=0%</td><td>signal image is entirely
- at the left speaker</td></tr>
-
-<tr><td>1</td><td>L=0% R=100%</td><td>signal image is entirely
- at the right speaker</td></tr>
-</table>
-
-<p>
- One way to remember this sort of convention is that the middle of the
- USA is not Kansas, but "Los Angeles: 50% New York: 50%".
-</p>
-
-<h3>Examples In Use</h3>
-
-<table>
-<tr><th>Appearance</th><th>Settings</th></tr>
-<tr><td><img src="/images/stereo-panner.png"></td><td>Width=100%,
- L=50 R=50</td></tr>
-<tr><td><img src="/images/stereo-panner-zero.png"></td><td>Width=0%,
- L=50 R=50</td></tr>
-<tr><td><img src="/images/stereo-panner-inverted.png"></td><td>Width=-100%, Position = 0 (center)</td></tr>
-<tr><td><img src="/images/stereo-panner-right.png"></td><td>Width=36%,
- L=44 R=56</td></tr>
-<tr><td><img src="/images/stereo-panner-hard-right.png"></td><td>Width=0%,
- L=0 R=100</td></tr>
-</table>
-
-<h4>Using the mouse</h4>
-
-<p>
- Mouse operations in the upper half of the panner adjust the position
- parameter, constrained by the current width setting.
-</p>
-<p>
- Mouse operations in the lower half of the panner adjust the width
- parameter, constrained by the current position setting.
-</p>
-<p>
- To change the position smoothly, press the right button and drag
- within the top half of the panner, then release. The position will
- be limited by the current width setting. <em>Note: you do not need
- to grab the position indicator in order to drag.</em>
-</p>
-<p>
- To change the width smoothly, press the right button and drag
- within the lower half of the panner, then release. The width will be
- limited by the current position setting. <em>Note: you do not need to
- grab the L/R indicators in order to drag.</em>
-</p>
-
-<dl class="faq">
-
-<dt>Reset to defaults</dt>
-<dd>Click <kbd class="mod3 mouse">right</kbd></dd>
-
-<dt>Change to hard left</dt>
-<dd>Double click <kbd class="mod2 mouse">right</kbd> in the upper left half
- of the panner</dd>
-
-<dt>Change to a hard right</dt>
-<dd>Double click <kbd class="mod2 mouse">right</kbd> in the upper right half
- of the panner</dd>
-
-<dt>Move position as far left as possible, given width</dt>
-<dd>Double click <kbd class="mouse">right</kbd> in the upper left half of the
- panner</dd>
-
-<dt>Move position as far right as possible, given width</dt>
-<dd>Double click <kbd class="mouse">right</kbd> in the upper right half of the
- panner</dd>
-
-<dt>Set the position to center</dt>
-<dd>Click <kbd class="mouse">right</kbd> in the upper middle of the panner</dd>
-
-<dt>Reset to maximum possible width</dt>
-<dd>Double click <kbd class="mouse">right</kbd> on the lower left side</dd>
-
-<dt>Invert (flip channel assignments)</dt>
-<dd>Double click <kbd class="mouse">right</kbd> on the lower right side</dd>
-
-<dt>Set width to 0°</dt>
-<dd>Double click <kbd class="mouse">right</kbd> in the lower middle</dd>
-</dl>
-
-<h4>Keyboard bindings</h4>
-
-<p>
- When the pointer is within a stereo panner user interface, the following
- keybindings are available to operate on that panner:
-</p>
-
-<dl>
- <dt><kbd>↑</kbd> / <kbd class="mod1">↑</kbd></dt>
- <dd>increase width by 1° / 5°</dd>
- <dt><kbd>↓</kbd> / <kbd class="mod1">↓</kbd></dt>
- <dd>decrease width by 1° / 5°</dd>
- <dt><kbd>←</kbd> / <kbd class="mod1">←</kbd></dt>
- <dd>move position 1° / 5° to the left</dd>
- <dt><kbd>→</kbd> / <kbd class="mod1">→</kbd></dt>
- <dd>move position 1° / 5° to the right</dd>
- <dt><kbd>0</kbd></dt>
- <dd>reset position to center</dd>
- <dt><kbd class="mod2">↑</kbd></dt>
- <dd>reset width to full (100%)</dd>
-</dl>
-
-<h4>Using the scroll wheel/touch scroll</h4>
-
-<p>
- When the pointer is within a stereo panner user interface, the scroll
- wheel may be used as follows:
-</p>
-
-<dl>
- <dt><kbd class="mouse">⇐</kbd> / <kbd class="mod1 mouse">⇐</kbd></dt>
- <dd>increase width by 1° / 5°</dd>
- <dt><kbd class="mouse">⇒</kbd> / <kbd class="mod1 mouse">⇒</kbd></dt>
- <dd>decrease width by 1° / 5°</dd>
- <dt><kbd class="mouse">⇑</kbd> / <kbd class="mod1 mouse">⇑</kbd></dt>
- <dd>move position 1° / 5° to the left</dd>
- <dt><kbd class="mouse">⇓</kbd> / <kbd class="mod1 mouse">⇓</kbd></dt>
- <dd>move position 1° / 5°to the right</dd>
-</dl>
-
-<h2><a name="caveat"></a>Stereo panning caveats</h2>
-
-<p class="warning">
-The stereo panner will introduce unwanted side effects on
-material that includes a time difference between the channels, such
-as A/B, ORTF or NOS microphone recordings, or delay-panned mixes.<br />
-When you reduce the with, you are effectively summing two highly
-correlated signals with a delay, which will cause <dfn>comb filtering</dfn>.
-</p>
-<p>
-Let's take a closer look at what happens when you record a source at 45° to the
-right side with an ORTF stereo microphone array and then manipulate the width.
-</p>
-<p>
-For testing, we apply a <dfn>pink noise</dfn> signal to both inputs of an Ardour stereo
-bus with the stereo panner, and feed the bus output to a two-channel analyser.
-Since pink noise contains equal energy per octave, the expected readout is a
-straight line, which would indicate that our signal chain does not color the
-sound:
-</p>
-<img src="/images/stereo-panner-with-ORTF-fullwidth.png" />
-<p>
-To simulate an ORTF, we use Robin Gareus' stereo balance
-control LV2 to set the level difference and time delay. Ignore the Trim/Gain
-— its purpose is just to align the test signal with the 0dB line of the
-analyser.
-</p>
-<p>
-Recall that an <dfn>ORTF</dfn> microphone pair consists of two cardioids spaced 17 cm
-apart, with an opening angle of 110°.
-For a far source at 45° to the right, the time difference between the capsules
-is 350 μs or approximately 15 samples at 44.1 kHz. The level difference
-due to the directivity of the microphones is about 7.5 dB (indicated by the
-distance between the blue and red lines in the analyser).
-</p>
-<p>
-Now for the interesting part: if we reduce the width of the signal to 50%,
-the time-delayed signals will be combined in the panner. Observe what
-happens to the frequency response of the left and right outputs:
-</p>
-<img src="/images/stereo-panner-with-ORTF-halfwidth.png" />
-<p>
-You may argue that all spaced microphone recordings will undergo comb
-filtering later, when the two channels recombine in the air between the speakers.
-Perceptually however, there is a huge of difference: our hearing system is
-very good at eliminating comb filters in the real world, where their component
-signals are spatially separated. But once you combine them
-inside your signal chain, this spatial separation is lost and the brain will
-no longer be able to sort out the timbral mess. As usual, you
-get to keep the pieces.
-</p>
-<p class="note">
-Depending on your material and on how much you need to manipulate the width,
-some degree of comb filtering may be acceptable. Then again, it may not. Listen
-carefully for artefacts if you manipulate unknown stereo signals — many
-orchestra sample libraries for example do contain time-delay components.
-</p>
-
-
projects / ardour-manual-diverged / blobdiff