position=center (L=50%, R=50%). This panner assumes that the signals
you wish to distribute are either uncorrelated (that means totally
independent), or they contain a stereo image which is
- mono-compatible<sup><ahref="#caveat">*</a></sup>.
+ mono-compatible, such as a co-incident microphone recording, or a
+ stereo image that has been created with pan pots.<sup><a href="#caveat">*</a></sup>
</p>
<div class="well">
<p>
<dd>move position 1° / 5°to the right</dd>
</dl>
-<h2><a name="caveat" />Panning caveats</h2>
+<h2><a name="caveat"></a>Panning caveats</h2>
-<p>
+<div class="well">
Note that the stereo panner will introduce unwanted side effects on
material that includes a time difference between the channels, such
as AB, ORTF or NOS microphone recordings, or delay-panned mixes.<br />
With such signals, when you reduce the with, you are summing two signals
with different delays, which will introduce comb filtering.
-</p>
+</div>
<p>
Let's take a look at what happens when you record a source at 45° to the
-right side with an ORTF array (cardioids, spacing 17cm, opening angle
-110°):<br />
-The time difference is 350 usecs or approximately 15 samples at 44k1. The
-level difference due to the directivity of the microphones is about 7.5dB.
+right side with an ORTF array and then manipulate the width.
+</p>
+<p>
+For testing, we apply a pink noise signal to both inputs of an Ardour stereo
+bus with the stereo panner, and feed the bus output to a two-channel analyser.
+Since pink noise contains equal energy per octave, the readout is a straight line:
</p>
<img src="/images/stereo-panner-with-ORTF-fullwidth.png" />
<p>
-For testing, we apply a pink noise signal, which displays as a straight line
-in the analyser. To simulate an ORTF, we use Robin Gareus' stereo balance
+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
+— its purpose is just to align the test signal with the 0dB line of the
analyser.
</p>
+<p>
+Recall that an ORTF microphone pair consists of two cardioids spaced 17 cm
+apart, with an opening angle of 110°.<br />
+For a source at 45° to the right, the time difference between the capsules
+is 350 usecs or approximately 15 samples at 44.1 kHz. The level difference
+due to the directivity of the microphones is about 7.5dB.
+</p>
<p>
Now for the interesting part: if we reduce the width of the signal to 50%,
the time-delayed signals will be combined in the panner. Observe what
-happens to the frequency response:
+happens to the frequency response of the left and right outputs:
</p>
<img src="/images/stereo-panner-with-ORTF-halfwidth.png" />
<p>
+You may argue that all spaced microphone recordings will get comb filters
+later, when the two channels recombine in the air between the speakers. But
+perceptually, this is a world of difference, since our hearing system is
+very good at eliminating comb filters in the real world, if their component
+signals are spatially separated. But once you combine two delayed signals
+inside your signal chain, this spatial separation is lost. As usual, you
+get to keep the pieces.
+</p>
+<div class="well">
Depending on your material and on how much you need to manipulate the width,
-the comb filter may be acceptable. Then again, it may not be. Listen
-carefully for artefacts if you manipulate unknown stereo signals - many
+the comb filter may be acceptable. Then again, it may not. Listen
+carefully for artefacts if you manipulate unknown stereo signals — many
orchestra sample libraries for example do contain time-delay components.
-</p>
+</div>
projects / ardour-manual-diverged / blobdiff