Topic: Is Roll-Off with Line In effective?

[Dede2002]

Well, zero knowledge on this matter. I've been reading old posts stating that if you're using Line In, the rolloff won't do a thing due to input impedance.
Is that right? Thanks in advance.

[Dede2002]

It depends.  A simple bass rolloff is usually done with a series capacitor.  That gives you 6dB/octave rolloff with the -3dB point ("corner frequency") defined by this formula:

frequency = 1/(2*pi*ohm*farad)

Thus the value of the capacitor (in farads, or likely microfarads, abbreviated uF--"u" is really Greek letter mu, but I digress . . .) has to be set in conjunction with the following input impedance, in ohms.  If a battery box is built expecting a given input impedance, say 2Kohms, then if a line input has 10Kohm input impedance, the corner frequency will be 5 times lower than intended.  That will not be much of a rolloff!

The battery box builder can either set the capacitor value for a particular input impedance, and knowing that it's a line input impedance, use a capacitor 1/5 the value.  The more sophisticated approach is to buffer the filter, such that the input impedance seen by the capacitor is fixed in the battery box, and the following device's input impedance is isolated from that filter.  But now we no longer have a simple battery box, but rather an amplifier.  And then we could get into more complicated filters once we have active components in the box . . .

Thanks for your reply. If I understood, everything depends on how a particular roll-off unit is designed/built. In my case (when I actually run a bb with roll-off it's a Microphone Madness model)  I feel and hear less bass. 

[adrianf74]

Yes, bass roll-off is device dependent.  My old Core Sound Battery Box did it via line-in as does my current Sound Professionals one.

Depending on the mics (and recorder) you're using you may want to be careful and limit your roll-off (or avoid it altogether).  I've got AT-943's and Chris Church suggested going flat. I've found the two shows I'd done (one a stadium and another an outdoor show) were way too boomy for my liking.  I've since done another outdoor show and an indoor club show with roll-off at 69Hz and fine this is a good compromise.  Lots of bass (maybe still a little too much) but I'd rather have too much than not enough as it can't be added back.

[Dede2002]

Yes, bass roll-off is device dependent.  My old Core Sound Battery Box did it via line-in as does my current Sound Professionals one.

Depending on the mics (and recorder) you're using you may want to be careful and limit your roll-off (or avoid it altogether).  I've got AT-943's and Chris Church suggested going flat. I've found the two shows I'd done (one a stadium and another an outdoor show) were way too boomy for my liking.  I've since done another outdoor show and an indoor club show with roll-off at 69Hz and fine this is a good compromise.  Lots of bass (maybe still a little too much) but I'd rather have too much than not enough as it can't be added back.

Hey, thanks a lot for your response, +T. I only use roll-off with my cards (MM-HLSO-Sennheiser MKE 2). Recorder is the Edirol R09HR. BB  with roll-off, of course, or CT-9100 pre. Any guess? Appreciate and thanks in advance 

[adrianf74]

Hey, thanks a lot for your response, +T. I only use roll-off with my cards (MM-HLSO-Sennheiser MKE 2). Recorder is the Edirol R09HR. BB  with roll-off, of course, or CT-9100 pre. Any guess? Appreciate and thanks in advance 

With the above, your roll off should work.  But Chris Church's advice rings true with Cards - use very little roll-off, if at all.  The Pre is no different than a "battery box"; it just allows you to ride the levels within as opposed to using the deck (and raising the noise floor to boot).

The only way to really know what your roll-off should be set to is through trial and error.  Chris had suggested not using any roll-off with my SP-CMC-8 (AT-943) mics as cards, in general, don't pick up as much bass.  However, the one stadium show and one outdoor show that I had recorded with my R-09 were a little boomy, so I raised the roll-off from FLAT (16Hz) to the first setting above (69Hz, in my case) and it makes a world of difference.

The thing Chris suggested is that it's always easier to remove excess bass in post; you can't ever ADD it back if its missing.  I prefer to muck around less in post and try to keep my masters sounding as "close" to the original recording if possible (i.e., no wav manipulation/eq'ing whenever possible). 

Hope I've helped.  I'd love to hear what your mics sound like, BTW.

[Dede2002]

Hey, thanks a lot for your response, +T. I only use roll-off with my cards (MM-HLSO-Sennheiser MKE 2). Recorder is the Edirol R09HR. BB  with roll-off, of course, or CT-9100 pre. Any guess? Appreciate and thanks in advance 

With the above, your roll off should work.  But Chris Church's advice rings true with Cards - use very little roll-off, if at all.  The Pre is no different than a "battery box"; it just allows you to ride the levels within as opposed to using the deck (and raising the noise floor to boot).

The only way to really know what your roll-off should be set to is through trial and error.  Chris had suggested not using any roll-off with my SP-CMC-8 (AT-943) mics as cards, in general, don't pick up as much bass.  However, the one stadium show and one outdoor show that I had recorded with my R-09 were a little boomy, so I raised the roll-off from FLAT (16Hz) to the first setting above (69Hz, in my case) and it makes a world of difference.

The thing Chris suggested is that it's always easier to remove excess bass in post; you can't ever ADD it back if its missing.  I prefer to muck around less in post and try to keep my masters sounding as "close" to the original recording if possible (i.e., no wav manipulation/eq'ing whenever possible). 

Hope I've helped.  I'd love to hear what your mics sound like, BTW.

Couldn't agree more with both you and Chris. I never use roll-off with my cards. HLSC-1 mics are great sounding mics, but not known for earth shaking bass, you know.
I also agree when you say that you are not a big fan of post production tricks. But in my experience, removing bass is not exactly an easy task. One has to really know what to do: which is the ressonant frequencies, at which particular frequency the filter has to be applied, the  filter curve( -6db, -12db or whatever) etc. Sometimes ( when I'm familiar with venue/band) I'd say: use roll-off. Doing so you can better capture the mids and highs, since your recorder is not handling massive lower frequency data.
Thanks a lot for your help. I'm going to send you a sample of my omnis.