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Author Topic: Compensating for cardioid bass roll off?  (Read 1280 times)

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Offline n3mmr

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Compensating for cardioid bass roll off?
« on: December 21, 2016, 04:19:50 AM »
I have been recording a small jazz band on and off for a few months now, and, comparing my recordings using line audio OM1 with those using the CM3, I realize that I should try to compensate for the bass rolloff in my CM3 mics.
Can anybody offer some practical advice or just share some experience of such processing?

I do realize this is venue- and setup dependent, since the proximity effect varies with incidence angle.


Offline Sloan Simpson

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Re: Compensating for cardioid bass roll off?
« Reply #1 on: December 21, 2016, 07:43:27 AM »
I use a Pultec-style EQ plugin for beefing up too-thin kick drums, specifically the Tube-Tech PE 1C



https://www.softube.com/index.php?id=pe1c
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Offline Gutbucket

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Re: Compensating for cardioid bass roll off?
« Reply #2 on: December 21, 2016, 10:12:22 AM »
Quote
I do realize this is venue- and setup dependent, since the proximity effect varies with incidence angle.

Proximity effect modifies low frequency response with respect to the distance of the microphone from the source, rather than angle of incidence.  Basically, it works in this way- at a specific distance, say 1 meter away as an example (realize that number will be different for other mics), the low frequency response curve will be essentially flat [edit- or rather, will match the manufacturer's published response curve].  Closer than that and the low frequencies are boosted, further away and they are attenuated.  It is true that the far off-axis response of a microphone is often different than the microphone's on-axis response, yet that difference remains more or less constant regardless of the distance of the microphone from the source.   So your EQ correction will vary depending on your recording setup- you'll end up with a different correction when recording on-stage with the microphones relatively close to the sources than you would with the microphones far back in the room.  And it will also vary from situation to situation and  from room to room.

Play around with EQ.  Try a simple low-frequency shelf filter to start, and adjust the corner frequency and boost values.  Compare recordings you've made of the same jazz band in the same room with the CM3s against the OM1s.  As an exercise, try to make the first sound as close to the second as possible, simply by listening and adjusting things, then once they are close, check out the values of the filter you've applied, or at least remember the shape of that curve.  That shape reflects the basic response difference between the two microphone pairs in that particular situation.  You can use a graphic EQ or peak filter parametric in the same way, which allows for further fine tuning of the curve, but start by approximating the shape of a shelf filter with them, and work from there.  Other recording situations may call for a different curve and different boost values, but the general shape will more or less be the same.  And once you've done that you have a handle a on a general baseline response difference between the two microphones. 

Next is to actually dial in an appropriate EQ correction for a specific recording.  The general response difference curve you figured out above may inform you somewhat as a starting point in dialing in a specific correction, but don't feel restricted by adhering strictly to it.  Each situation calls for a somewhat different correction and different variables come into play.  You may want more or less low-frequency information in general, or need to address a specific resonant frequency range or reduce HVAC rumble or whatever.  There is no single objectively correct EQ correction for each particular recording, only a subjectively correct correction for each listener, and hopefully that corresponds closely with what you like and what you hear through your playback system.

I will say this- I rarely, if ever, find that a low-cut filter is a "musically correct" choice.  Many seem to advocate chopping everything off below a certain frequency range, but I tend to hear problems with the "chop off the lowest stuff" approach even when the playback system is incapable of reproducing those lowest frequencies.  Sometimes it's necessary to salvage a recording, but I always find a shelf-filter if not a more complex curve made with parametric peak filters or a graphic eq corrects low-frequency problems in far better sounding ways which don't do as much or more harm than good. 

With that in mind, consider the response of your monitoring equipment when making these kinds of decisions.  Since that is what you are listening through when making EQ decisions, the tendency will be to compensate for the deficiencies of the playback system as well as those of the recording.  You end up adjusting things to make the recording sound great (to you) through your system.  But when you listen on another system, the corrections may not sound right, and it's the part of the correction which was fixing the specifics of your playback system and not the part of it correcting the microphone and overall recording responses which doesn't "travel well".  You can learn to "hear around that problem" by listening to recordings you've worked on through a number of different systems, through a few different headphones, in the car, etc. until you sort of figure out what works more or less everywhere, learn what that sounds like through the system you use to edit, and begin to use that as an internal objective reference.
« Last Edit: December 22, 2016, 03:13:13 PM by Gutbucket »
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Offline morst

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Re: Compensating for cardioid bass roll off?
« Reply #3 on: December 22, 2016, 02:27:01 PM »
I realize that I should try to compensate for the bass rolloff in my CM3 mics.

If you are cutting low frequencies with a bass roll-off filter, try it without the filter. Those things are not for music, more for speech.
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Offline n3mmr

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Re: Compensating for cardioid bass roll off?
« Reply #4 on: December 28, 2016, 12:46:13 PM »
I realize I went at this from the wrong angle.

I will start a new thread where I discuss various aspects of using directional microphones, compensated for a particular point source distance, when used in realistic environments.
This is nowhere near as straightforward as some think, yet there are very straightforward strategies for dealing with the problems one may encounter.

Offline voltronic

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Re: Compensating for cardioid bass roll off?
« Reply #5 on: December 28, 2016, 02:52:57 PM »
How far away are you recording the band?  Two thoughts, though neither is a post-fix:

1. Why not combine your CM3s with OM1s in a Tony-Faulkner style 4-mic phased array?  The combination compensates nicely for distance, within reason.  I don't have OM1s, but have used my CM3s in this way when I can not record as close as I'd like, with great results.  If you're not familiar with this:
https://youtu.be/AchMeIIVxb4?t=1026
http://taperssection.com/index.php?topic=172679.0

2. Omnis won't lose the bass at distance obviously, but will lose treble.  So, use a pair of omnis that are diffuse-field equalized, such as DPA 406x with the short boost grids, DPA 4006 with diffuse grid, Schoeps MK 2H / 2S, etc.
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Offline if_then_else

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Re: Compensating for cardioid bass roll off?
« Reply #6 on: December 29, 2016, 11:26:34 AM »
How far away are you recording the band?  Two thoughts, though neither is a post-fix:

1. Why not combine your CM3s with OM1s in a Tony-Faulkner style 4-mic phased array?  The combination compensates nicely for distance, within reason.  I don't have OM1s, but have used my CM3s in this way when I can not record as close as I'd like, with great results.  If you're not familiar with this:
https://youtu.be/AchMeIIVxb4?t=1026
http://taperssection.com/index.php?topic=172679.0


If memory serves, the OM1 are free field omnis and they work best when mounted close to the source (also because of their **relatively** high self noise 18dB(A)). If you're going to run some Faulkner-style array from a distance, you might want to use proper diffuse field omnis.

I've only used them once in a 4-mic-array and that was very close to the stage.

Offline Gutbucket

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Re: Compensating for cardioid bass roll off?
« Reply #7 on: December 29, 2016, 12:31:39 PM »
No need to let the native response of your microphones dictate the microphone arrangement.  That's putting the cart before the horse.  Turn it the right way around by choosing an appropriate microphone arrangement to suit the situation, then tailoring frequency response as necessary.  Sure, choose the most appropriate mics you have available to you, but don't let not having a particular type stop you.  Run whatever omnis you have on hand, and EQ the output to sound the way you want it. 

Its simple to EQ a "free field" response omni to match the response of a "diffuse field" omni, or vice versa.  Doing so is more straightforward than EQing the low frequency response of a cardioid to compensate for roll-off or proximity boost, which was the original question posed in the thread.  But either way, just use whatever EQ adjustment sounds most appropriate, rather than trying to apply some sort of formulaic compensation curve.  You will probably develop a general idea of what correction you typically end up with, and can use that as a good starting point the next time around when the arrangement and conditions are similar, but I'd still suggest dialing in the most optimal correction by ear. 

As always when making these kinds of decisions, use monitoring you trust and know how it translates elsewhere, but the same applies to any decision you make based on "how it sounds", be that EQ decisions, switching microphones, configurations or whatever.

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