Thursday, September 13, 2007

First Question, Surround Mixing

The first question comes from Miles:

I would like to post a question regarding surround-sound mixing.

It seems one of the biggest mistakes or miscalculations surround sound mixers make is how to handle the low end; proper bass management.

I hear a lot of mixes with the bass rolled off heavily, or accentuated extensively. The mixer doesn't intend on those drastic differences but the mix reads so violently different from system to system (speaking of the low end only here!).

"Surround-Sound" systems are so common now amongst consumers that I wondered how mixers are achieving proper bass management in their mixes and what are some of the techniques used to check yourself?

Leave your comments below.


seriousfun said...

Great question.

Bass Management is a term that refers to integrating a subwoofer with main speakers in a speaker system. It was coined in the last century by Tony Grimani and Tomlinson Holman at Lucasfilm in the THX division, as a way to describe the process to allow consumers with average systems and rooms to play all channels of film sound full-range.

Properly mixing and mastering bass content in a surround music mix is a different subject. Since the advent of CD, mixes have been done from one or more channels of acquired audio to two channels which can deliver full-range sound - 20 to 20k Hz, wide dynamic range, low noise, etc. Now (well, for about 15 years now) we have not two but five full-range channels to deliver music, and an additional limited-range channel for low-frequency effects, included to extend the headroom of cinema systems.

How is bass content treated for a 5.1 Stereo mix? The same as in a 2.0 Stereo mix (stereo does not mean two, it means solid). But, we now have five full-range channels to deliver bass instruments, giving us an opportunity for a tremendous increase in headroom.

Bass instruments traditionally, especially for delivery on LP records, were mixed equally in both speakers, in-part to take advantage of two channels of record grooves, cabling, pre-amplification, power amplification, etc. We have gotten used to an un-natural representation of acoustic events, for example a jazz quartet where the acoustic bass player is positioned on the left but the 2.0 Stereo mix of this presents him from the center. 5.1 Stereo gives us the opportunity to position him properly without losing headroom, without the needle jumping from the groove, etc.

In no situation should bass content be mixed to the LFE channel. "Because it is there" is no reason to misuse this feature. There is more than enough headroom for our delivery systems, rooms, and ear/brain mechanisms to perceive any low-frequency occurance properly delivered by one or more of the main channels without using the LFE channel. Using the LFE channel is a guarantee of phase and time problems that will lead to inconsistent translation of that mix from the mixing and mastering studio to the consumer.

The monitoring system should be full-range. Either use five truly full-range speakers plus a subwoofer dedicated to the LFE (if needed for film work), or five limited-range speakers properly integrated with a subwoofer with Bass Management.

Surround music mixing is liberating!

Anonymous said...

I think some of Seriousfun's comments contradicted each other. With a 2 channel mix, I try to check my mix on as many different systems as possible. One of his comments really got to me: "In no situation should bass content be mixed to the LFE channel". That seems a bit closed minded, don't ya think? If you have ever used a subwoofer in your mixes, it is essentially an LFE channel, controlled by the sub's settings instead of the mixing engineer's. I prefer to take the guess work away from the sub, and make it proper to begin with.

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