-When you reduce the with, you are effectively summing two highly -correlated signals with a delay, which will cause comb filtering. +When the width is reduced, two highly correlated signals with a delay are +effectively summed, which will cause comb filtering.
-Let's take a closer look at what happens when you record a source at 45° to the -right side with an ORTF stereo microphone array and then manipulate the width. +Let's take a closer look at what happens when a source is recorded at 45° to the +right side with an ORTF stereo microphone array and then the width manipulated.
For testing, we apply a pink noise signal to both inputs of an Ardour stereo @@ -211,40 +208,52 @@ straight line, which would indicate that our signal chain does not color the sound:
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+ - 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. + An ORTF is simulated using Robin Gareus' stereo balance control LV2 to set the + level difference and time delay. The Trim/Gain can be ignored—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 far source at 45° to the right, the time difference between the capsules -is 350 μs or approximately 15 samples at 44.1 kHz. The level difference -due to the directivity of the microphones is about 7.5 dB (indicated by the -distance between the blue and red lines in the analyser). + An ORTF microphone pair consists of two cardioids spaced 17 cm + apart, with an opening angle of 110°. For a far source at 45° to the + right, the time difference between the capsules is 350 μs or + approximately 15 samples at 44.1 kHz. The level difference due to the + directivity of the microphones is about 7.5 dB (indicated by the distance + between the blue and red lines in the analyser).
-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 of the left and right outputs: + Now for the interesting part: if the width of the signal is reduced to 50%, + the time-delayed signals will be combined in the panner. What happens to the + frequency response of the left and right outputs is shown in the following + picture:
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+ -You may argue that all spaced microphone recordings will undergo comb -filtering later, when the two channels recombine in the air between the speakers. -Perceptually however, there is a huge of difference: our hearing system is -very good at eliminating comb filters in the real world, where their component -signals are spatially separated. But once you combine them -inside your signal chain, this spatial separation is lost and the brain will -no longer be able to sort out the timbral mess. As usual, you -get to keep the pieces. + It can be argued that all spaced microphone recordings will undergo comb + filtering later, when the two channels recombine in the air between the + speakers. Perceptually however, there is a huge difference: our hearing + system is very good at eliminating comb filters in the real world, where their + component signals are spatially separated. But once they are combined inside + a signal chain, this spatial separation is lost and the brain will no + longer be able to sort out the timbral mess.
-Depending on your material and on how much you need to manipulate the width, -some degree of comb filtering 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. + Depending on the material and on how much the width needs to be manipulated, + some degree of comb filtering may be acceptable. Then again, it may not. + It is advised to listen carefully for artefacts when manipulating unknown stereo + signals—many orchestra sample libraries for example do contain + time-delay components.
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