Live recording with selectable bass roll-off...

[cjd]

Hi all,

New to the forum, and have trolled long enough to learn a lot of excellent stuff. While I've been able to find a lot of good info on using battery-boxes to achieve bass roll-off in boomy halls or bass-heavy concerts, I haven't seen anyone post their experiences with microphone madness products (specifically the "Mint-Box" 7-position roll-off battery box which I ordered today (link))

I've tried building my own battery boxes with some success, but have been unable to achieve any dramatic reduction in bass. In particular, there is a comedy club that I like to tape in that has a lot of hall-boom. Even with my battery box that has 2.2 microfarad capacitors I'm unable to roll off as much bass as I'd like. I'm usually using a pair of Core Sound low-cost binaurals with my MZ-NH900, which are by far my most bass-heavy mics for some reason... But the capsules are better matched than I can do on my own, so I end up using them instead on one of my homemade cardioid pairs which tend to pick up a lot less of the low end.

I was skeptical of the Mint Box because I have always been under the impression that you are supposed to use capacitors made specifically for audio applications. Since these are usually old-fashioned mylar film or polypropylene (read: LARGE) capacitors, it's obvious that they aren't using 7 pairs of these in the tiny Mint Box. The person I e-mailed at Microphone madness (understandably) wouldn't tell me anything about the electronic components used in making the battery box.

So I took a chance, and hope that it works out. I'd feel better if there were someone who could tell me their experience with MM's products.

Thanks-

Chris

Edited August 10, 2005 by cjd

[greenmachine]

Using a filter before the signal reaches the recorder is some kind of a guesswork, you won't know how it will sound in the end. You can be lucky to find a well balanced setting for a particular location, but often you won't and desire to correct the low frequency amount afterwards a second time. That said, before filtering too much i'd rather filter nothing at all and do all the fine-tuning afterwards in an audio editor.

By the way, this is the formula for calculating the capacity value for a certain cutoff frequency: C = 1 / (2 * Pi * R * fc)

R being the recorder's input impedance. For a cutoff at 150 Hz and an input impedance of 10 kOhm, your cap would have to have about 0.1 µF. A value as large as 2.2 µF would cut below the audible range (subsonics).

A short overview why cardioids often ain't as bassy as omnis: Cardioids tend to suffer from the proximity effect: At a certain distance (about 1' usually) they pick up the low frequency region more or less linear, if you move closer to the source, the bass will be exaggerated - if you move farther, bass will be rolled off. Omnis don't show this effect, they're more or less linear at any distance.

[cjd]

Using a filter before the signal reaches the recorder is some kind of a guesswork, you won't know how it will sound in the end. You can be lucky to find a well balanced setting for a particular location, but often you won't and desire to correct the low frequency amount afterwards a second time. That said, before filtering too much i'd rather filter nothing at all and do all the fine-tuning afterwards in an audio editor.

←

Thanks for the info, especially the explanation of why cardioid-pattern microphones are less bass-heavy. I did not know that that was why, though it makes a lot of sense.

With just my home computer and Audacity, I have been unable to satisfactorily cut out enough bass from the recordings I make with my Core Sound Binaurals. Perhaps someone could steer me toward a program that incorporates a good equalizer that I could run the sound through post-recording. In my experience, cutting out the bass (what little was cut out by using my homemade battery-box through line-in) while making the live recording seemed a good idea. I should post a snippet of a recording so you can hear how rumbly and boomy it can be in one of the rooms that I record in. I had the good fortune to get the same seat twice (near a wall, even, for extra boom) and recorded first with no roll-off through mic-in, then with the battery box through line-in and the difference, while not profound, was noticeable. I am worried, as you mentioned, that I will cut out too much low-end, which cannot be repaired later, of course. I'm also worried that there's so much low-end without the roll-off that it will "muddy" the recording no mater what I do with it after it's recorded. It's a tough call.

Maybe there's a plug-in for Audacity that permits adjustment of levels? I'm new enough to this that I just don't know...

[greenmachine]

No need for additional software yet. You can use the embedded 'Equalization' effect to create your own rolloff curve in Audacity. It works well, is easy to use and looks like that:

[cjd]

Wow.

How did I miss that? Now that I've tried that out, I see that I've got a lot of work to do on a stack of old recordings. I does work well! Thanks for pointing that out to me.