---
<p>
-The default stereo panner distributes 2 inputs to 2 outputs. Its
-behaviour is controlled by two parameters, width and position. The
-default settings for the stereo panner
-are width=100%>, position=center (L=50%,
-R=50%). This panner assumes that you have 2 uncorrelated,
-independent signals that you wish to distribute to two outputs.
+ The default stereo panner distributes 2 inputs to 2 outputs. Its
+ behaviour is controlled by two parameters, width and position. The
+ default settings for the stereo panner are width=100%,
+ position=center (L=50%, R=50%). This panner assumes that the signals
+ you wish to distribute are either uncorrelated (that means totally
+ independent), or they contain a stereo image which is
+ mono-compatible, such as a co-incident microphone recording, or a
+ stereo image that has been created with pan pots.<sup><a href="#caveat">*</a></sup>
</p>
<div class="well">
<p>
single signal indicator marked "M" (for mono), and 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
</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%".
+ 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>
<h2>Examples In Use</h2>
<h2>Using the mouse</h2>
-<p>Mouse operations in the upper half of the panner adjust the position
+<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
+<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
+<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
+<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>
<h4>Keyboard bindings</h4>
-When the pointer is within a stereo panner user interface, the following
-keybindings are available to operate on that panner:
+<p>
+ When the pointer is within a stereo panner user interface, the following
+ keybindings are available to operate on that panner:
+</p>
<dl>
<dt><key>↑</key> / <key class="mod1">↑</key></dt>
<dt><key>0</key></dt>
<dd>reset position to center</dd>
<dt><key class="mod2">↑</key></dt>
- <dd>reset width to 180° (100%)</dd>
+ <dd>reset width to full (100%)</dd>
</dl>
<h4>Using the scroll wheel/touch scroll</h4>
-When the pointer is within a stereo panner user interface, the scroll
-wheel may be used as follows:
+<p>
+ When the pointer is within a stereo panner user interface, the scroll
+ wheel may be used as follows:
+</p>
<dl>
<dt>left / <key class="mod1">left</key></dt>
<dt>down / <key class="mod1">down</key></dt>
<dd>move position 1° / 5°to the right</dd>
</dl>
+
+<h2><a name="caveat"></a>Panning caveats</h2>
+
+<div class="well">
+Note that the stereo panner will introduce unwanted side effects on
+material that includes a time difference between the channels, such
+as AB, ORTF or NOS microphone recordings, or delay-panned mixes.<br />
+With such signals, when you reduce the with, you are summing two signals
+with different delays, which will introduce comb filtering.
+</div>
+<p>
+Let's take a look at what happens when you record a source at 45° to the
+right side with an ORTF array and then manipulate the width.
+</p>
+<p>
+For testing, we apply a pink noise 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 readout is a straight line:
+</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 ORTF microphone pair consists of two cardioids spaced 17 cm
+apart, with an opening angle of 110°.<br />
+For a source at 45° to the right, the time difference between the capsules
+is 350 usecs or approximately 15 samples at 44.1 kHz. The level difference
+due to the directivity of the microphones is about 7.5dB.
+</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 get comb filters
+later, when the two channels recombine in the air between the speakers. But
+perceptually, this is a world of difference, since our hearing system is
+very good at eliminating comb filters in the real world, if their component
+signals are spatially separated. But once you combine two delayed signals
+inside your signal chain, this spatial separation is lost. As usual, you
+get to keep the pieces.
+</p>
+<div class="well">
+Depending on your material and on how much you need to manipulate the width,
+the comb filter 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.
+</div>
+
projects / ardour-manual-diverged / blobdiff