7 The default stereo panner distributes two inputs to two outputs. Its
8 behaviour is controlled by two parameters, <em>width</em> and
10 default settings for the stereo panner are <em>width=100%</em> and
11 <em>position=center</em>.
12 This stereo panner assumes that the signals
13 you wish to distribute are either uncorrelated (i.e. totally
14 independent), or that they contain a stereo image which is
15 <em>mono-compatible</em>, such as a co-incident microphone recording, or a
16 sound stage that has been created with pan pots.<sup><a href="#caveat">*</a></sup>
20 With the default values it is not possible to alter the position,
21 since the width is already spread entirely across both outputs. To
22 alter the position, you must first reduce the width.
26 <h2>Stereo Panner User Interface</h2>
28 <img src="/images/stereo-panner-annotated.png" alt=""/>
31 The panner user interface consists of three elements, divided between
32 the top and bottom half. Click and/or drag in the top half to
33 control position; click and/or drag in the bottom half to control
34 width (see below for details).
37 In the top half is the position indicator, which shows where the
38 center of the stereo image is relative to the left and right
39 edges. When this is the middle of the panner, the stereo image is
40 centered between the left and right outputs. When it all the way to
41 the left, the stereo image collapses to just the left speaker.
44 In the bottom half are two signal indicators, one marked "L" and the
45 other "R". The distance between these two shows the width of the
46 stereo image. If the width is reduced to zero, there will only be a
47 single signal indicator marked "M" (for mono), whose color will
48 change to indicate the special state.
51 It is possible to invert the outputs (see below) so that whatever
52 would have gone to the right channel goes to the left and vice
53 versa. When this happens, the entire movable part of the panner
54 changes color to indicate clearly that this is the case.
57 <h3>Position vs. L/R</h3>
60 Although the implementation of the panner uses the "position"
61 parameter, when the user interface displays it numerically, it shows a pair of numbers that
62 will be familiar to most audio engineers.
66 <tr><th>Position</th><th>L/R</th><th>English</th></tr>
67 <tr><td>0</td><td>L=50% R=50%</td><td>signal image is midway between
68 left and right speakers</td></tr>
70 <tr><td>-1</td><td>L=100% R=0%</td><td>signal image is entirely
71 at the left speaker</td></tr>
73 <tr><td>1</td><td>L=0% R=100%</td><td>signal image is entirely
74 at the right speaker</td></tr>
78 One way to remember this sort of convention is that the middle of the
79 USA is not Kansas, but "Los Angeles: 50% New York: 50%".
82 <h2>Examples In Use</h2>
85 <tr><th>Appearance</th><th>Settings</th></tr>
86 <tr><td><img src="/images/stereo-panner.png"></td><td>Width=100%,
88 <tr><td><img src="/images/stereo-panner-zero.png"></td><td>Width=0%,
90 <tr><td><img src="/images/stereo-panner-inverted.png"></td><td>Width=-100%, Position = 0 (center)</td></tr>
91 <tr><td><img src="/images/stereo-panner-right.png"></td><td>Width=36%,
93 <tr><td><img src="/images/stereo-panner-hard-right.png"></td><td>Width=0%,
97 <h2>Using the mouse</h2>
100 Mouse operations in the upper half of the panner adjust the position
101 parameter, constrained by the current width setting.
104 Mouse operations in the lower half of the panner adjust the width
105 parameter, constrained by the current position setting.
108 To change the position smoothly, press the right button and drag
109 within the top half of the panner, then release. The position will
110 be limited by the current width setting. <em>Note: you do not need
111 to grab the position indicator in order to drag</em>
114 To change the width smoothly, press the right button and drag
115 within the lower half of the panner, then release. The width will be
116 limited by the current position setting.<em>Note: you do not need to
117 grab the L/R indicators in order to drag</em>
122 <dt>Reset to defaults</dt>
123 <dd>Click <key class="mod3">right button</key></dd>
125 <dt>Change to a "hard left"</dt>
126 <dd>Double click <key class="mod2">right button</key> in the upper left half
129 <dt>Change to a "hard right"</dt>
130 <dd>Double click <key class="mod2">right button</key> in the upper right half
133 <dt>Move position as far left as possible, given width</dt>
134 <dd>Double click <key>right button</key> in the upper left half of the
137 <dt>Move position as far right as possible, given width</dt>
138 <dd>Double click <key>right button</key> in the upper right half of the
141 <dt>Set the position to center</dt>
142 <dd>Click <key>right button</key> in the upper middle of the panner</dd>
144 <dt>Reset to maximum possible width</dt>
145 <dd>Double click <key>right button</key> on the lower left side</dd>
147 <dt>Invert (flip channel assignments)</dt>
148 <dd>Double click <key>right button</key> on the lower right side</dd>
150 <dt>Set width to 0°</dt>
151 <dd>Double click <key>right button</key> in the lower middle</dd>
154 <h4>Keyboard bindings</h4>
157 When the pointer is within a stereo panner user interface, the following
158 keybindings are available to operate on that panner:
162 <dt><key>↑</key> / <key class="mod1">↑</key></dt>
163 <dd>increase width by 1° / 5°</dd>
164 <dt><key>↓</key> / <key class="mod1">↓</key></dt>
165 <dd>decrease width by 1° / 5°</dd>
166 <dt><key>←</key> / <key class="mod1">←</key></dt>
167 <dd>move position 1° / 5° to the left</dd>
168 <dt><key>→</key> / <key class="mod1">→</key></dt>
169 <dd>move position 1° / 5° to the right</dd>
170 <dt><key>0</key></dt>
171 <dd>reset position to center</dd>
172 <dt><key class="mod2">↑</key></dt>
173 <dd>reset width to full (100%)</dd>
176 <h4>Using the scroll wheel/touch scroll</h4>
179 When the pointer is within a stereo panner user interface, the scroll
180 wheel may be used as follows:
184 <dt>left / <key class="mod1">left</key></dt>
185 <dd>increase width by 1° / 5°</dd>
187 <dt>right / <key class="mod1">right</key></dt>
188 <dd>decrease width by 1° / 5°</dd>
190 <dt>up / <key class="mod1">up</key></dt>
191 <dd>move position 1° / 5° to the left</dd>
193 <dt>down / <key class="mod1">down</key></dt>
194 <dd>move position 1° / 5°to the right</dd>
197 <h2><a name="caveat"></a>Stereo panning caveats</h2>
200 The stereo panner will introduce unwanted side effects on
201 material that includes a time difference between the channels, such
202 as A/B, ORTF or NOS microphone recordings, or delay-panned mixes.<br />
203 When you reduce the with, you are effectively summing two highly
204 correlated signals with a delay, which will cause comb filtering.
207 Let's take a closer look at what happens when you record a source at 45° to the
208 right side with an ORTF stereo microphone array and then manipulate the width.
211 For testing, we apply a pink noise signal to both inputs of an Ardour stereo
212 bus with the stereo panner, and feed the bus output to a two-channel analyser.
213 Since pink noise contains equal energy per octave, the expected readout is a
214 straight line, which would indicate that our signal chain does not color the
217 <img src="/images/stereo-panner-with-ORTF-fullwidth.png" />
219 To simulate an ORTF, we use Robin Gareus' stereo balance
220 control LV2 to set the level difference and time delay. Ignore the Trim/Gain
221 — its purpose is just to align the test signal with the 0dB line of the
225 Recall that an ORTF microphone pair consists of two cardioids spaced 17 cm
226 apart, with an opening angle of 110°.
227 For a far source at 45° to the right, the time difference between the capsules
228 is 350 μs or approximately 15 samples at 44.1 kHz. The level difference
229 due to the directivity of the microphones is about 7.5 dB (indicated by the
230 distance between the blue and red lines in the analyser).
233 Now for the interesting part: if we reduce the width of the signal to 50%,
234 the time-delayed signals will be combined in the panner. Observe what
235 happens to the frequency response of the left and right outputs:
237 <img src="/images/stereo-panner-with-ORTF-halfwidth.png" />
239 You may argue that all spaced microphone recordings will undergo comb
240 filtering later, when the two channels recombine in the air between the speakers.
241 Perceptually however, there is a huge of difference: our hearing system is
242 very good at eliminating comb filters in the real world, where their component
243 signals are spatially separated. But once you combine them
244 inside your signal chain, this spatial separation is lost and the brain will
245 no longer be able to sort out the timbral mess. As usual, you
246 get to keep the pieces.
249 Depending on your material and on how much you need to manipulate the width,
250 some degree of comb filtering may be acceptable. Then again, it may not. Listen
251 carefully for artefacts if you manipulate unknown stereo signals — many
252 orchestra sample libraries for example do contain time-delay components.