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>
19 With the default values it is not possible to alter the position,
20 since the width is already spread entirely across both outputs. To
21 alter the position, you must first reduce the width.
24 <h2>Stereo Panner User Interface</h2>
26 <img src="/images/stereo-panner-annotated.png" alt=""/>
29 The panner user interface consists of three elements, divided between
30 the top and bottom half. Click and/or drag in the top half to
31 control position; click and/or drag in the bottom half to control
32 width (see below for details).
35 In the top half is the position indicator, which shows where the
36 center of the stereo image is relative to the left and right
37 edges. When this is the middle of the panner, the stereo image is
38 centered between the left and right outputs. When it all the way to
39 the left, the stereo image collapses to just the left speaker.
42 In the bottom half are two signal indicators, one marked "L" and the
43 other "R". The distance between these two shows the width of the
44 stereo image. If the width is reduced to zero, there will only be a
45 single signal indicator marked "M" (for mono), whose color will
46 change to indicate the special state.
49 It is possible to invert the outputs (see below) so that whatever
50 would have gone to the right channel goes to the left and vice
51 versa. When this happens, the entire movable part of the panner
52 changes color to indicate clearly that this is the case.
55 <h3>Position vs. L/R</h3>
58 Although the implementation of the panner uses the "position"
59 parameter, when the user interface displays it numerically, it shows a pair of numbers that
60 will be familiar to most audio engineers.
64 <tr><th>Position</th><th>L/R</th><th>English</th></tr>
65 <tr><td>0</td><td>L=50% R=50%</td><td>signal image is midway between
66 left and right speakers</td></tr>
68 <tr><td>-1</td><td>L=100% R=0%</td><td>signal image is entirely
69 at the left speaker</td></tr>
71 <tr><td>1</td><td>L=0% R=100%</td><td>signal image is entirely
72 at the right speaker</td></tr>
76 One way to remember this sort of convention is that the middle of the
77 USA is not Kansas, but "Los Angeles: 50% New York: 50%".
80 <h3>Examples In Use</h3>
83 <tr><th>Appearance</th><th>Settings</th></tr>
84 <tr><td><img src="/images/stereo-panner.png"></td><td>Width=100%,
86 <tr><td><img src="/images/stereo-panner-zero.png"></td><td>Width=0%,
88 <tr><td><img src="/images/stereo-panner-inverted.png"></td><td>Width=-100%, Position = 0 (center)</td></tr>
89 <tr><td><img src="/images/stereo-panner-right.png"></td><td>Width=36%,
91 <tr><td><img src="/images/stereo-panner-hard-right.png"></td><td>Width=0%,
95 <h4>Using the mouse</h4>
98 Mouse operations in the upper half of the panner adjust the position
99 parameter, constrained by the current width setting.
102 Mouse operations in the lower half of the panner adjust the width
103 parameter, constrained by the current position setting.
106 To change the position smoothly, press the right button and drag
107 within the top half of the panner, then release. The position will
108 be limited by the current width setting. <em>Note: you do not need
109 to grab the position indicator in order to drag</em>
112 To change the width smoothly, press the right button and drag
113 within the lower half of the panner, then release. The width will be
114 limited by the current position setting.<em>Note: you do not need to
115 grab the L/R indicators in order to drag</em>
120 <dt>Reset to defaults</dt>
121 <dd>Click <key class="mod3">right button</key></dd>
123 <dt>Change to a "hard left"</dt>
124 <dd>Double click <key class="mod2">right button</key> in the upper left half
127 <dt>Change to a "hard right"</dt>
128 <dd>Double click <key class="mod2">right button</key> in the upper right half
131 <dt>Move position as far left as possible, given width</dt>
132 <dd>Double click <key>right button</key> in the upper left half of the
135 <dt>Move position as far right as possible, given width</dt>
136 <dd>Double click <key>right button</key> in the upper right half of the
139 <dt>Set the position to center</dt>
140 <dd>Click <key>right button</key> in the upper middle of the panner</dd>
142 <dt>Reset to maximum possible width</dt>
143 <dd>Double click <key>right button</key> on the lower left side</dd>
145 <dt>Invert (flip channel assignments)</dt>
146 <dd>Double click <key>right button</key> on the lower right side</dd>
148 <dt>Set width to 0°</dt>
149 <dd>Double click <key>right button</key> in the lower middle</dd>
152 <h4>Keyboard bindings</h4>
155 When the pointer is within a stereo panner user interface, the following
156 keybindings are available to operate on that panner:
160 <dt><key>↑</key> / <key class="mod1">↑</key></dt>
161 <dd>increase width by 1° / 5°</dd>
162 <dt><key>↓</key> / <key class="mod1">↓</key></dt>
163 <dd>decrease width by 1° / 5°</dd>
164 <dt><key>←</key> / <key class="mod1">←</key></dt>
165 <dd>move position 1° / 5° to the left</dd>
166 <dt><key>→</key> / <key class="mod1">→</key></dt>
167 <dd>move position 1° / 5° to the right</dd>
168 <dt><key>0</key></dt>
169 <dd>reset position to center</dd>
170 <dt><key class="mod2">↑</key></dt>
171 <dd>reset width to full (100%)</dd>
174 <h4>Using the scroll wheel/touch scroll</h4>
177 When the pointer is within a stereo panner user interface, the scroll
178 wheel may be used as follows:
182 <dt>left / <key class="mod1">left</key></dt>
183 <dd>increase width by 1° / 5°</dd>
185 <dt>right / <key class="mod1">right</key></dt>
186 <dd>decrease width by 1° / 5°</dd>
188 <dt>up / <key class="mod1">up</key></dt>
189 <dd>move position 1° / 5° to the left</dd>
191 <dt>down / <key class="mod1">down</key></dt>
192 <dd>move position 1° / 5°to the right</dd>
195 <h2><a name="caveat"></a>Stereo panning caveats</h2>
198 The stereo panner will introduce unwanted side effects on
199 material that includes a time difference between the channels, such
200 as A/B, ORTF or NOS microphone recordings, or delay-panned mixes.<br />
201 When you reduce the with, you are effectively summing two highly
202 correlated signals with a delay, which will cause comb filtering.
205 Let's take a closer look at what happens when you record a source at 45° to the
206 right side with an ORTF stereo microphone array and then manipulate the width.
209 For testing, we apply a pink noise signal to both inputs of an Ardour stereo
210 bus with the stereo panner, and feed the bus output to a two-channel analyser.
211 Since pink noise contains equal energy per octave, the expected readout is a
212 straight line, which would indicate that our signal chain does not color the
215 <img src="/images/stereo-panner-with-ORTF-fullwidth.png" />
217 To simulate an ORTF, we use Robin Gareus' stereo balance
218 control LV2 to set the level difference and time delay. Ignore the Trim/Gain
219 — its purpose is just to align the test signal with the 0dB line of the
223 Recall that an ORTF microphone pair consists of two cardioids spaced 17 cm
224 apart, with an opening angle of 110°.
225 For a far source at 45° to the right, the time difference between the capsules
226 is 350 μs or approximately 15 samples at 44.1 kHz. The level difference
227 due to the directivity of the microphones is about 7.5 dB (indicated by the
228 distance between the blue and red lines in the analyser).
231 Now for the interesting part: if we reduce the width of the signal to 50%,
232 the time-delayed signals will be combined in the panner. Observe what
233 happens to the frequency response of the left and right outputs:
235 <img src="/images/stereo-panner-with-ORTF-halfwidth.png" />
237 You may argue that all spaced microphone recordings will undergo comb
238 filtering later, when the two channels recombine in the air between the speakers.
239 Perceptually however, there is a huge of difference: our hearing system is
240 very good at eliminating comb filters in the real world, where their component
241 signals are spatially separated. But once you combine them
242 inside your signal chain, this spatial separation is lost and the brain will
243 no longer be able to sort out the timbral mess. As usual, you
244 get to keep the pieces.
247 Depending on your material and on how much you need to manipulate the width,
248 some degree of comb filtering may be acceptable. Then again, it may not. Listen
249 carefully for artefacts if you manipulate unknown stereo signals — many
250 orchestra sample libraries for example do contain time-delay components.