Roger Dressler (formerly of Dolby Labs and the guy who helped them develop many of their technologies, including bass management) and
Mark Seaton (founder and owner of Seaton Sound, makers of the legendary Submersive subwoofers) have both recently put forward an alternative view. Mark explains it like this in
this post:
"I personally tend to set the low pass on the LFE channel at 80Hz in most systems by preference. I think many forget that the difference between a 120Hz low pass and an 80Hz low pass is nothing more than a shelving filter. If the low pass is 4th order, the 80Hz filter is about 7dB lower at 100Hz and about 4dB at 80Hz. A 100Hz low pass setting would have about 1/2 that difference. The adjustment has more effect on shaping the LFE track's response than it does on cutting off content. If you're running the subs with a rising response on the low end which blends with the main speakers, experimenting with 80, 100 vs. 120Hz is basically a means to taper the top end of the LFE channel. Setting this lower than 120Hz is not hacking off content any more than setting your sub a few dB hot would destroy a soundtrack."
What this means in effect is that you do NOT lose the content between 80Hz and 120Hz if you set the LPF of LFE to 80Hz - you simply alter the way it is presented, because the filter is not a brickwall but a shelving filter. Setting it to 80Hz simply allows you to 'shape' the LFE track's response.
Roger goes on to elaborate more in
a separate post (my bolding below):
"Back when DTS was making their name with Jurassic Park and Apollo 13 on 35mm film, the LFE bandwidth was 80 Hz. The Dolby Digital codec has a bandlimited LFE channel, and it has a brickwall filter at 120 Hz as a means to protect the LFE channel from higher frequencies (which can still be present even with a 4th-order LPF at 80 Hz). It seems that when films moved from optical to digital delivery, the LFE bandwidth crept up to 120 Hz or maybe even higher (the PCM LFE channel has no inherent response limitation). I suppose it helps less than magnificent subwoofers in "regular" cinemas provide more whomp. But I find that LFE in the 100-120 Hz region is just a lot of boominess that unfortunately too often clouds the deeper bass in the bottom 2 octaves. Setting the LFE filter to 80 Hz does a dandy job of dealing with that boominess IMHO.
In addition, I have found that 5.1 music recordings are not well disciplined in their use of LFE, leading to muddiness that is even more annoying. Again, the 80 Hz LFE filter setting really helps the bass knit together more cohesively." Background information also in
this post of Roger's.
