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In Reply to: Re: Bass management or LFE low-pass filtering is required if using a sub posted by Robert C. Lang on December 2, 2005 at 18:26:34:
well, you have probably touched on a very complex and thorny topic where these is a lot of divergent opinion. I don't claim to have the last word, or even the correct word, so take my comments with a grain of salt.first of all, low frequencies are more susceptible to phase cancellation simply due to the length of the waves.
For example, if you have two speakers generating exactly the same low frequency but they happen to be spaced exactly one half of the wave length apart (from the perspective of the listener) then you may get complete wave cancellation.
For this reason, some engineers recommend avoiding low frequencies on all channels. However, there are many examples of recordings with strong bass information on all channels (eg. the SFS Mahlers seem to contain strong bass in the surround channels, but also many pop/rock recordings).
"Consolidating" the low frequencies into a .1 channel have the benefit of avoiding destructive phase cancellation, particularly if you also manipulate the phase of the signals being consolidated to avoid any gross instances of phase cancellation in the mixing itself.
However, the counter argument is that the subwoofer then becomes a "single point of failure". You may get impaired bass response depending on listener or subwoofer position due to phase cancellation from room reflections. Arguably having more than one low frequency driver averages out room interaction issues.
I don't think there is a clear answer. My advice is get a subwoofer (ideally, two, placed opposite each other) for any recordings with a discrete .1, but use it solely for that purpose and avoid bass management. That way, if there is bass information in the main channels, they will be reproduced by the main channels, but if there is a discrete .1 channel, that gets reproduced by the subwoofer. Presumably, this replicates what the engineer was hearing, so if there was any bass issues they would have been fixed in the mix.
But, as always, your specific situation may demand a different solution. I highly recommend buying a measurement mic (like a Behringer ECM8000) and do room measurements. I've been using RoomEQWizard (a freeware program) and the results have been very surprising (to me).
I'm also considering digital room correction - I've been monitoring the progress of a open source plugin to Windows Media Player called Convolver. It's capable of doing real time high resolution room correction for multiple channels (but you need a very powerful PC - I'm using a dual core 3GHz processor). Of course, this only works for CDs and DVD-As, not for SA-CD (unless I digitize the output of my SA-CD player into PCM which I'm reluctant to do).
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Follow Ups
- Re: Bass management or LFE low-pass filtering is required if using a sub - Christine Tham 21:12:08 12/02/05 (3)
- Re: Bass management or LFE low-pass filtering is required if using a sub - Dave Kingsland 10:59:26 12/03/05 (1)
- That's not as bad as you think - Christine Tham 15:08:42 12/03/05 (0)
- Some examples of "surprising" results I found for my room ... - Christine Tham 22:16:11 12/02/05 (0)
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