@@ -191,40 +191,57 @@ title: Stereo Panner
Panning caveats
+Panning caveats
-+
With such signals, when you reduce the with, you are summing two signals with different delays, which will introduce comb filtering. - +
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°):
-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.
+
+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:
-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.
+
+Recall that an ORTF microphone pair consists of two cardioids spaced 17 cm
+apart, with an opening angle of 110°.
+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.
+
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:
-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 -orchestra sample libraries for example do contain time-delay components. +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.
+