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 to distribute are either uncorrelated
9 (i.e. totally independent), or that they contain a stereo image which is
10 <dfn>mono-compatible</dfn>, such as a co-incident microphone recording, or a
11 sound stage that has been created with pan pots.<sup><a href="#caveat">*</a></sup>
14 With the default values it is not possible to alter the position,
15 since the width is already spread entirely across both outputs. To
16 alter the position, the width must first be reduced.
19 <h2>Stereo Panner User Interface</h2>
22 <img src="/images/stereo-panner.png" alt="The Stereo Panner">
29 The <dfn>panner user interface</dfn> consists of three elements, divided between
30 the top and bottom half. Clicking and/or dragging in the top half
31 controls position; clicking and/or dragging in the bottom half controls
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 <kbd class="menu">L</kbd> and the
43 other <kbd class="menu">R</kbd>. 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 <kbd class="menu">M</kbd> (for mono), whose color will
46 change to indicate this 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
60 a pair of numbers that 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>
67 <tr><td>-1</td><td>L=100% R=0%</td><td>signal image is entirely
68 at the left speaker</td></tr>
69 <tr><td>1</td><td>L=0% R=100%</td><td>signal image is entirely
70 at the right speaker</td></tr>
74 One way to remember this sort of convention is that the middle of the
75 USA is not Kansas, but "Los Angeles: 50% New York: 50%".
78 <h3>Examples In Use</h3>
81 <tr><th>Appearance</th><th>Settings</th></tr>
82 <tr><td><img src="/images/stereo-panner.png"></td><td>Width=100%,
84 <tr><td><img src="/images/stereo-panner-zero.png"></td><td>Width=0%,
86 <tr><td><img src="/images/stereo-panner-inverted.png"></td><td>Width=-100%, Position = 0 (center)</td></tr>
87 <tr><td><img src="/images/stereo-panner-right.png"></td><td>Width=36%,
89 <tr><td><img src="/images/stereo-panner-hard-right.png"></td><td>Width=0%,
93 <h4>Using the mouse</h4>
96 Mouse operations in the upper half of the panner adjust the position
97 parameter, constrained by the current width setting.
100 Mouse operations in the lower half of the panner adjust the width
101 parameter, constrained by the current position setting.
104 The position can be changed smoothly, by pressing the right button and dragging
105 within the top half of the panner, then releasing. The position will
106 be limited by the current width setting. <em>Note: it is not necessary
107 to grab the position indicator in order to drag.</em>
110 The width can also be changed smoothly, by pressing the right button and dragging
111 within the lower half of the panner, then releasing. The width will be
112 limited by the current position setting. <em>Note: it is not necessary
113 to grab the L/R indicators in order to drag.</em>
118 <tr><th>Reset to defaults</th>
119 <td>Click <kbd class="mod3 mouse">right</kbd></td></tr>
121 <tr><th>Change to hard left</th>
122 <td>Double click <kbd class="mod2 mouse">right</kbd> in the upper left half
123 of the panner</td></tr>
125 <tr><th>Change to a hard right</th>
126 <td>Double click <kbd class="mod2 mouse">right</kbd> in the upper right half
127 of the panner</td></tr>
129 <tr><th>Move position as far left as possible, given width</th>
130 <td>Double click <kbd class="mouse">right</kbd> in the upper left half of the
133 <tr><th>Move position as far right as possible, given width</th>
134 <td>Double click <kbd class="mouse">right</kbd> in the upper right half of the
137 <tr><th>Set the position to center</th>
138 <td>Click <kbd class="mouse">right</kbd> in the upper middle of the panner</td></tr>
140 <tr><th>Reset to maximum possible width</th>
141 <td>Double click <kbd class="mouse">right</kbd> on the lower left side</td></tr>
143 <tr><th>Invert (flip channel assignments)</th>
144 <td>Double click <kbd class="mouse">right</kbd> on the lower right side</td></tr>
146 <tr><th>Set width to 0°</th>
147 <td>Double click <kbd class="mouse">right</kbd> in the lower middle</td></tr>
150 <h4>Keyboard bindings</h4>
153 When the pointer is within a stereo panner user interface, the following
154 keybindings are available to operate on that panner:
158 <tr><th><kbd>↑</kbd> / <kbd class="mod1">↑</kbd></th>
159 <td>increase width by 1° / 5°</td></tr>
160 <tr><th><kbd>↓</kbd> / <kbd class="mod1">↓</kbd></th>
161 <td>decrease width by 1° / 5°</td></tr>
162 <tr><th><kbd>←</kbd> / <kbd class="mod1">←</kbd></th>
163 <td>move position 1° / 5° to the left</td></tr>
164 <tr><th><kbd>→</kbd> / <kbd class="mod1">→</kbd></th>
165 <td>move position 1° / 5° to the right</td></tr>
166 <tr><th><kbd>0</kbd></th>
167 <td>reset position to center</td></tr>
168 <tr><th><kbd class="mod2">↑</kbd></th>
169 <td>reset width to full (100%)</td></tr>
172 <h4>Using the scroll wheel/touch scroll</h4>
175 When the pointer is within a stereo panner user interface, the scroll
176 wheel may be used as follows:
180 <tr><th><kbd class="mouse">⇐</kbd> / <kbd class="mod1 mouse">⇐</kbd></th>
181 <td>increase width by 1° / 5°</td></tr>
182 <tr><th><kbd class="mouse">⇒</kbd> / <kbd class="mod1 mouse">⇒</kbd></th>
183 <td>decrease width by 1° / 5°</td></tr>
184 <tr><th><kbd class="mouse">⇑</kbd> / <kbd class="mod1 mouse">⇑</kbd></th>
185 <td>move position 1° / 5° to the left</td></tr>
186 <tr><th><kbd class="mouse">⇓</kbd> / <kbd class="mod1 mouse">⇓</kbd></th>
187 <td>move position 1° / 5°to the right</td></tr>
190 <h2><a name="caveat"></a>Stereo panning caveats</h2>
193 The stereo panner will introduce unwanted side effects on
194 material that includes a time difference between the channels, such
195 as A/B, ORTF or NOS microphone recordings, or delay-panned mixes.<br>
196 When the width is reduced, two highly correlated signals with a delay are
197 effectively summed, which will cause <dfn>comb filtering</dfn>.
200 Let's take a closer look at what happens when a source is recorded at 45° to the
201 right side with an ORTF stereo microphone array and then the width manipulated.
204 For testing, we apply a <dfn>pink noise</dfn> signal to both inputs of an Ardour stereo
205 bus with the stereo panner, and feed the bus output to a two-channel analyser.
206 Since pink noise contains equal energy per octave, the expected readout is a
207 straight line, which would indicate that our signal chain does not color the
211 <figure class="center">
212 <img src="/images/stereo-panner-with-ORTF-fullwidth.png" alt="Stereo panner
213 with ORTF fullwidth">
214 <figcaption>Stereo panner with ORTF full width</figcaption>
218 An ORTF is simulated using Robin Gareus' stereo balance control LV2 to set the
219 level difference and time delay. The Trim/Gain can be ignored—its purpose
220 is just to align the test signal with the 0dB line of the analyser.
224 An <dfn>ORTF</dfn> microphone pair consists of two cardioids spaced 17 cm
225 apart, with an opening angle of 110°. For a far source at 45° to the
226 right, the time difference between the capsules is 350 μs or
227 approximately 15 samples at 44.1 kHz. The level difference due to the
228 directivity of the microphones is about 7.5 dB (indicated by the distance
229 between the blue and red lines in the analyser).
232 Now for the interesting part: if the width of the signal is reduced to 50%,
233 the time-delayed signals will be combined in the panner. What happens to the
234 frequency response of the left and right outputs is shown in the following
238 <figure class="center">
239 <img src="/images/stereo-panner-with-ORTF-halfwidth.png" alt="Stereo panner
240 with ORTF halfwidth">
241 <figcaption>Stereo panner with ORTF half width</figcaption>
245 It can be argued that all spaced microphone recordings will undergo comb
246 filtering later, when the two channels recombine in the air between the
247 speakers. Perceptually however, there is a huge difference: our hearing
248 system is very good at eliminating comb filters in the real world, where their
249 component signals are spatially separated. But once they are combined inside
250 a signal chain, this spatial separation is lost and the brain will no
251 longer be able to sort out the timbral mess.
254 Depending on the material and on how much the width needs to be manipulated,
255 some degree of comb filtering may be acceptable. Then again, it may not.
256 It is advised to listen carefully for artefacts when manipulating unknown stereo
257 signals—many orchestra sample libraries for example do contain
258 time-delay components.