7 The default <dfn>stereo panner</dfn> distributes two inputs to two outputs. Its
8 behaviour is controlled by two parameters, <dfn>width</dfn> and
9 <dfn>position</dfn>. By default, the panner is centered at full width.
13 The stereo panner assumes that the signals
14 you wish to distribute are either uncorrelated (i.e. totally
15 independent), or that they contain a stereo image which is
16 <dfn>mono-compatible</dfn>, such as a co-incident microphone recording, or a
17 sound stage that has been created with pan pots.<sup><a href="#caveat">*</a></sup>
21 With the default values it is not possible to alter the position,
22 since the width is already spread entirely across both outputs. To
23 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 <dfn>panner user interface</dfn> 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).
38 In the top half is the position indicator, which shows where the
39 center of the stereo image is relative to the left and right
40 edges. When this is the middle of the panner, the stereo image is
41 centered between the left and right outputs. When it all the way to
42 the left, the stereo image collapses to just the left speaker.
46 In the bottom half are two signal indicators, one marked "L" and the
47 other "R". The distance between these two shows the width of the
48 stereo image. If the width is reduced to zero, there will only be a
49 single signal indicator marked "M" (for mono), whose color will
50 change to indicate the special state.
54 It is possible to invert the outputs (see below) so that whatever
55 would have gone to the right channel goes to the left and vice
56 versa. When this happens, the entire movable part of the panner
57 changes color to indicate clearly that this is the case.
60 <h3>Position vs. L/R</h3>
63 Although the implementation of the panner uses the "position"
64 parameter, when the user interface displays it numerically, it shows
65 a pair of numbers that will be familiar to most audio engineers.
69 <tr><th>Position</th><th>L/R</th><th>English</th></tr>
70 <tr><td>0</td><td>L=50% R=50%</td><td>signal image is midway between
71 left and right speakers</td></tr>
73 <tr><td>-1</td><td>L=100% R=0%</td><td>signal image is entirely
74 at the left speaker</td></tr>
76 <tr><td>1</td><td>L=0% R=100%</td><td>signal image is entirely
77 at the right speaker</td></tr>
81 One way to remember this sort of convention is that the middle of the
82 USA is not Kansas, but "Los Angeles: 50% New York: 50%".
85 <h3>Examples In Use</h3>
88 <tr><th>Appearance</th><th>Settings</th></tr>
89 <tr><td><img src="/images/stereo-panner.png"></td><td>Width=100%,
91 <tr><td><img src="/images/stereo-panner-zero.png"></td><td>Width=0%,
93 <tr><td><img src="/images/stereo-panner-inverted.png"></td><td>Width=-100%, Position = 0 (center)</td></tr>
94 <tr><td><img src="/images/stereo-panner-right.png"></td><td>Width=36%,
96 <tr><td><img src="/images/stereo-panner-hard-right.png"></td><td>Width=0%,
100 <h4>Using the mouse</h4>
103 Mouse operations in the upper half of the panner adjust the position
104 parameter, constrained by the current width setting.
107 Mouse operations in the lower half of the panner adjust the width
108 parameter, constrained by the current position setting.
111 To change the position smoothly, press the right button and drag
112 within the top half of the panner, then release. The position will
113 be limited by the current width setting. <em>Note: you do not need
114 to grab the position indicator in order to drag.</em>
117 To change the width smoothly, press the right button and drag
118 within the lower half of the panner, then release. The width will be
119 limited by the current position setting. <em>Note: you do not need to
120 grab the L/R indicators in order to drag.</em>
125 <dt>Reset to defaults</dt>
126 <dd>Click <kbd class="mod3 mouse">right</kbd></dd>
128 <dt>Change to hard left</dt>
129 <dd>Double click <kbd class="mod2 mouse">right</kbd> in the upper left half
132 <dt>Change to a hard right</dt>
133 <dd>Double click <kbd class="mod2 mouse">right</kbd> in the upper right half
136 <dt>Move position as far left as possible, given width</dt>
137 <dd>Double click <kbd class="mouse">right</kbd> in the upper left half of the
140 <dt>Move position as far right as possible, given width</dt>
141 <dd>Double click <kbd class="mouse">right</kbd> in the upper right half of the
144 <dt>Set the position to center</dt>
145 <dd>Click <kbd class="mouse">right</kbd> in the upper middle of the panner</dd>
147 <dt>Reset to maximum possible width</dt>
148 <dd>Double click <kbd class="mouse">right</kbd> on the lower left side</dd>
150 <dt>Invert (flip channel assignments)</dt>
151 <dd>Double click <kbd class="mouse">right</kbd> on the lower right side</dd>
153 <dt>Set width to 0°</dt>
154 <dd>Double click <kbd class="mouse">right</kbd> in the lower middle</dd>
157 <h4>Keyboard bindings</h4>
160 When the pointer is within a stereo panner user interface, the following
161 keybindings are available to operate on that panner:
165 <dt><kbd>↑</kbd> / <kbd class="mod1">↑</kbd></dt>
166 <dd>increase width by 1° / 5°</dd>
167 <dt><kbd>↓</kbd> / <kbd class="mod1">↓</kbd></dt>
168 <dd>decrease width by 1° / 5°</dd>
169 <dt><kbd>←</kbd> / <kbd class="mod1">←</kbd></dt>
170 <dd>move position 1° / 5° to the left</dd>
171 <dt><kbd>→</kbd> / <kbd class="mod1">→</kbd></dt>
172 <dd>move position 1° / 5° to the right</dd>
173 <dt><kbd>0</kbd></dt>
174 <dd>reset position to center</dd>
175 <dt><kbd class="mod2">↑</kbd></dt>
176 <dd>reset width to full (100%)</dd>
179 <h4>Using the scroll wheel/touch scroll</h4>
182 When the pointer is within a stereo panner user interface, the scroll
183 wheel may be used as follows:
187 <dt><kbd class="mouse">⇐</kbd> / <kbd class="mod1 mouse">⇐</kbd></dt>
188 <dd>increase width by 1° / 5°</dd>
189 <dt><kbd class="mouse">⇒</kbd> / <kbd class="mod1 mouse">⇒</kbd></dt>
190 <dd>decrease width by 1° / 5°</dd>
191 <dt><kbd class="mouse">⇑</kbd> / <kbd class="mod1 mouse">⇑</kbd></dt>
192 <dd>move position 1° / 5° to the left</dd>
193 <dt><kbd class="mouse">⇓</kbd> / <kbd class="mod1 mouse">⇓</kbd></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 width, you are effectively summing two highly
204 correlated signals with a delay, which will cause <dfn>comb filtering</dfn>.
208 Let's take a closer look at what happens when you record a source at 45° to the
209 right side with an ORTF stereo microphone array and then manipulate the width.
213 For testing, we apply a <dfn>pink noise</dfn> signal to both inputs of an Ardour stereo
214 bus with the stereo panner, and feed the bus output to a two-channel analyser.
215 Since pink noise contains equal energy per octave, the expected readout is a
216 straight line, which would indicate that our signal chain does not color the
220 <img src="/images/stereo-panner-with-ORTF-fullwidth.png" />
223 To simulate an ORTF, we use Robin Gareus' stereo balance
224 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
229 Recall that an <dfn>ORTF</dfn> microphone pair consists of two cardioids
230 spaced 17 cm apart, with an opening angle of 110°. For a far source at
231 45° to the right, the time difference between the capsules is 350 μs
232 or approximately 15 samples at 44.1 kHz. The level difference due to the
233 directivity of the microphones is about 7.5 dB (indicated by the
234 distance between the blue and red lines in the analyser).
238 Now for the interesting part: if we reduce the width of the signal to 50%,
239 the time-delayed signals will be combined in the panner. Observe what
240 happens to the frequency response of the left and right outputs:
243 <img src="/images/stereo-panner-with-ORTF-halfwidth.png" />
246 You may argue that all spaced microphone recordings will undergo comb
247 filtering later, when the two channels recombine in the air between the speakers.
248 Perceptually however, there is a huge of difference: our hearing system is
249 very good at eliminating comb filters in the real world, where their component
250 signals are spatially separated. But once you combine them
251 inside your signal chain, this spatial separation is lost and the brain will
252 no longer be able to sort out the timbral mess. As usual, you
253 get to keep the pieces.
257 Depending on your material and on how much you need to manipulate the width,
258 some degree of comb filtering may be acceptable. Then again, it may not. Listen
259 carefully for artefacts if you manipulate unknown stereo signals—many
260 orchestra sample libraries for example do contain time-delay components.