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Join Date: Oct 2001
Location: Monterey Park, CA
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Your subwoofer receives 2 types of low frequencies: derived bass, which is filtered from any speaker set to Small; and discrete bass, which is from the discrete LFE channel of any soundtrack that ends in ".1" (e.g., 5.1 or 6.1 soundtracks). Your receiver allows you to control each of those types of bass independently of each other. Consider yourself lucky.
When listening to 2-channel material, derived bass is sent to your subwoofer. There is no .1 channel. When listening to 5.1 material, derived bass and discrete bass are mixed and sent to your subwoofer. This can sometimes overwhelm the sub and make it bottom out, or even just be distracting when you're trying to follow important dialogue.
If you want to lower the overall level of the subwoofer, you can use sub level adjustment. But then you'll have deviated from calibrated levels and your subwoofer will be out of balance with the rest of your speakers.
However, if you feel that a particular soundtrack is sending too much bass to your subwoofer, then you can adjust the amount of LFE content being sent to your sub without changing the overall subwoofer level. That's what the LFE attenuator is for.
Unlike the subwoofer level adjustment, which lets you adjust the overall subwoofer volume level up or down, the LFE attenuator work in one direction: down. That's because you can't add more LFE than there is in the soundtrack, you can only attenuate (lower) it.
With less discrete LFE bass going to the sub, it will naturally become a little softer and keep your sub from bottoming out.
When you initially set up your subwoofer, I would leave the LFE attenuator at 0 (zero). IF you hear distortion, only then would I start to lessen the amount of LFE content being sent to the sub. Otherwise there no need to adjust this parameter.