# Movie mixing and bass management



## JeffKnob (May 30, 2007)

I have been wondering about this for a while so hopefully someone can provide me with some insight. When the sound guy mixes the audio track for a movie, there will be 5-7 full range channels and the .1 LFE. The LFE will have items specifically intended only for that channel. In our receivers we use bass management to take some of the low end frequencies from the 5-7 full range channels and add them to the .1 LFE channel. My question is if we are supposed to do this due to the omni-directional nature of the .1 LFE channel then why does the audio engineer even mix the sound into the 5-7 channels instead of just putting it into the .1 LFE channel from the start? On that note, if the audio engineer wants the sound coming from the 5-7 channels then in theory wouldn't the best setup actually be to have 5-7 truly full range speakers and a subwoofer for only the sound originally mixed for the .1 LFE channel?

I understand the theory behind the omni-directional nature of sub 120hz sound so I am not debating that. I just was curious about why it isn't just mixed with that in mind.


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## AudiocRaver (Jun 6, 2012)

JeffKnob said:


> My question is if we are supposed to do this due to the omni-directional nature of the .1 LFE channel then why does the audio engineer even mix the sound into the 5-7 channels instead of just putting it into the .1 LFE channel from the start? On that note, if the audio engineer wants the sound coming from the 5-7 channels then in theory wouldn't the best setup actually be to have 5-7 truly full range speakers and a subwoofer for only the sound originally mixed for the .1 LFE channel?


Yes, to be "most like the engineer," you would use full-range speakers and have the sub carry only the .1 LFE signal.



> I understand the theory behind the omni-directional nature of sub 120hz sound so I am not debating that. I just was curious about why it isn't just mixed with that in mind.


Actually, it is more broadly accepted that above about 80 Hz the sound starts to become directional. But you have the right idea. In a larger theater or mixing room, there are more timing issues to deal with and it is better to let the full-range speakers carry their full-range signal. In a home theater, letting the sub handle all sound below 80 Hz is more practical.


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## AudioPost (Feb 26, 2013)

JeffKnob said:


> My question is if we are supposed to do this due to the omni-directional nature of the .1 LFE channel then why does the audio engineer even mix the sound into the 5-7 channels instead of just putting it into the .1 LFE channel from the start?


In a way, you are thinking about this backwards, the clue is in the name of the ".1" channel. The Low Frequency Effects channel is specifically for low frequency sound effects, not for general bass. The 3-5 main (front) speakers are perfectly capable of producing a balanced bass response. The LFE channel is generally used when one doesn't want a balanced bass response, for example, when one wants to move a great deal of air to give the audience an actual physical sensation of say a crash, an explosion or some other type of big impact.



JeffKnob said:


> On that note, if the audio engineer wants the sound coming from the 5-7 channels then in theory wouldn't the best setup actually be to have 5-7 truly full range speakers and a subwoofer for only the sound originally mixed for the .1 LFE channel?


In theory "yes", in practise "not necessarily"! You are incorrectly assuming that the audio mix on the film you are watching is the original theatrical mix. Unless you can get hold of an actual distribution DCP, there's a fairly high probability that the mix you're listening to on your BluRay, DVD or stream has been re-mixed and optimised for home use. IE. The theatrical mix has had it's dynamic range significantly reduced, plus various other tweaks may have been applied to compensate for the differences between a theatrical sound system and a home sound system. In other words, to get closer to the audio engineer (Re-recording Mixer) of the home distribution mix, the ideal system is most likely to be; a good quality, standard bass-managed home cinema system!

G


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