Topic: bass rolloff (mic, preamp, phantom power?)

[T.J.]

    After snooping around this site (and others) I have yet to find a clear explaination of what bass rolloff actually is. From what I've gathered bass rolloff is a setting found on a variety of equipment.  It helps to filter out noise, and other extremely loud levels to avoid distortion.  I've seen bass rolloff mentioned in discussions about mics, preamps, and phantom power. 
    Now, say as an example you were running a set of AKG 483 -> Lunatec V3 -> M1.  I know the V3 serves as phantom power to power the mics, but will it also have some type of bass rolloff to eliminate high levels?  Can this be adjusted using the GAIN and TRIM settings of the V3 (or is this something completely different). Is bass rolloff necessary? please help!! i'm confused

[mirth]

bass rolloff will trim the low levels, not high levels like you said in your question.

Basically, when you're at a super bassy show rolloff could help to get a clearer, less muddy sounding recording.

That being said, I tried the rolloff switch on my mics (AKG 393) at a STS9 show once and it made it utterly lifeless sounding. You could just tell from listening to it that something was missing. I'd rather record something unaltered and then clean it up in post... You can always EQ your tape after the fact, but if its removed before the sound hits tape or disk then its gone forever.

[AlphaQuam]

I agree with Mirth... if the mics can handle it, don't use any rolloff.  Basically it's a cut that starts at a certain frequency (such as 90Hz) and fades the levels down to zero (such as 12dB/octave).  Imagine the left half of something like -1/10x^2.

[Brian Skalinder]

    After snooping around this site (and others) I have yet to find a clear explaination of what bass rolloff actually is. From what I've gathered bass rolloff is a setting found on a variety of equipment.  It helps to filter out noise, and other extremely loud levels to avoid distortion.  I've seen bass rolloff mentioned in discussions about mics, preamps, and phantom power. 
    Now, say as an example you were running a set of AKG 483 -> Lunatec V3 -> M1.  I know the V3 serves as phantom power to power the mics, but will it also have some type of bass rolloff to eliminate high levels?  Can this be adjusted using the GAIN and TRIM settings of the V3 (or is this something completely different). Is bass rolloff necessary? please help!! i'm confused

Yes, many preamps have HPF options.  HPF = high pass filter, aka bass rolloff.  It's basically a way of attenuating, or reducing, the lower frequencies.  It doesn't directly relate to your amplitude levels and shouldn't be used as a utility for reducing your levels, though attenuating the bass will generally lower your levels some.

Very simplisticly, let's take a recording that is (for the sake of easy ASCII illustration) flat across all frequencies:

low                        high
_______________________________

Though flat, the recording may be overly bass-heavy, be too strong in the low frequencies, which can cause the recording to sound, for example, muddy.  Or just plain overly bass-heavy with the bass frequencies overwhelming the others to the point that the low end dominates the sound of the recording.  A HPF will reduce the bass frequencies.  For example, like this:

low                        high
    ___________________________
    /
  /
/

The general settings that impact the effect of rolloff are starting point and slope.  The starting point defines at what point in the frequency range (measured in Hz) to begin applying the rolloff slope. The slope determines how steep a slope to rolloff (measured in dB / octave).  The steeper the slope the more bass reduction you'll have below your defined starting point.

You can apply a HPF either in-line at the time of recording, for example with a preamp (or with a switch on some mics), or you can apply the HPF in post-production on your audio workstation.  In-line HPFs typicall have fixed starting points and slopes, sometimes 2 different options.  As you can imagine, not a lot of flexibility there.  The benefit of applying it in post-production is that you can tailor the HPF very specifically to the recording by selecting any starting point whatsoever, and definining the slope however you see fit.  Don't like the starting point or slope, undo the operation and try again until you find one you like.

To answer a couple specific questions, the V3 has a HPF option for each channel, the options being 0 (off), 1 (on), 2(on).  The difference between 1 and 2 lie in the starting point at which the HPF is configured to rolloff, and the slope of the rolloff.  The gain and trim levels are used to adjust amplitude only and do not affect frequency.

I don't think I've ever used a HPF in-line when recording, though others may have.  Is it necessary?  In the vast majority of situations, I'd say no.

[T.J.]

wow,
thanks brian. that has really set me on the right track by clearing up some basics...I may have a couple more questions, but I have sort through some of my other resources before posting.  but, just to recap what everyone has said on this thread (so i can get it straight in my head):

-bass rolloff =HPF (high pass filter)
-this primarily deals with low frequencies
-if when recording, you notice the sound being recorded is muddled (very bassy) this could be caused by low frequency sounds overpowering the higher frequencies.
-if this occurs, you can reduce the amount of low frequency sound by utilizing HPF (ex: the HPF switch on the V3 would roll off  bass (or low frequencies) if switched to 1, and roll off even more bass if switched to 2)
-HPF is normally not necessary except in extreme circumstances

[jhirte]

I run the rolloff on my v3 on occasion, mainly at a certain venue, since they usually have the low end CRANKED.
Running AKG 461 -> V3.
Normally I run it 75hz @ 6db octave. I'm gonna try it at 100Hz to see what it sounds like as 75hz isn't quite enough for this venue IMO.

Options on V3 for rolloff:

1 is high 2 low: 125hz/75hz or 100hz/50hz. so in position 1, rolloff starts at 125hz or 100hz depending on how you set the jumpers. 2 is 75hz or 50hz (again, depending on jumper settings). Then you can also adjust the amount of rolloff in DB per octave, choices are 6db or 12db (first order and second order? I cant recall). This is also a jumper setting, and cannot be done "on the fly". I've been leaving it on 6db/octave. I ran a few shows at 100hz 12db too much low end cut! boo! heh.

And I just realized I just gave info that can be found in the online manual. hehe I suck.

BUt Tenacious, hope this helps... more often than not, your gonna leave it all alone and it'll be fine. Mainly for REALLY boomy rooms or a room where the soundperson loves the bass drum thumping your chest.

-Jim

[dklein]

I run 50 Hz. 12dB/octave HPF almost every time.  Everything booms around here.

[leegeddy]

nice explanation, brian.

marc