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