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Author Topic: theory: favoring high-boost caps on DPA (and similar) omnis  (Read 3824 times)

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Offline dabbler

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theory: favoring high-boost caps on DPA (and similar) omnis
« on: March 24, 2015, 03:46:43 AM »
If you do not like post-processing/EQ at all, I suggest you stop reading now :)

So the more I think about this, the more it makes sense to be recording with high boost grids with DPA 406x (and similar mics) instead of soft boost grids; then finally EQ away the excess in post after applying gain.

Like most folks, I prefer to set levels conservatively to avoid surprise overloads.  Most of my recordings peak around -12 to -5 dB, sometimes less.

However, my recording peaks are always in the low and mid regions:
excess bass due to room gain, audience clapping/screaming, or even a mic impact (mine or the performer)

The "air" regions are barely present at all and are likely to get lost in the noise floor.  So, there should be more than enough headroom to accomodate the 10dB boost centered at 12kHz (looks like 0.707 Q) from the DPA graphs.

If I want a flatter recording after post, I'd add gain to boost all frequencies first, then drop to counter the boost as much as I need.

So something like the following sox command:

   sox $IN.flac $OUT.flac gain $DB equalizer 12000 0.707q -10

For removing the soft-boost, it might be:

   sox $IN.flac $OUT.flac gain $DB equalizer 15000 0.707q -3

Of course, the exact levels and widths can be tweaked accordingly in case of obstructions and such, and recordings typically benefit from good EQ anyways IMHO.

SoX also has a nice --plot option to visualize equalizer adjustments (assuming you you're using a *nix system with gnuplot and sox installed):

   sox --plot=gnuplot >/tmp/plot -n -n equalizer $FREQ $WIDTH $GAIN
   gnuplot /tmp/plot

Anyways I'll test this theory at upcoming shows to see if things are acceptable after post with high boost grids.

Offline Gutbucket

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Re: theory: favoring high-boost caps on DPA (and similar) omnis
« Reply #1 on: March 24, 2015, 09:51:18 AM »
If you like, call it an acoustic "pre-emphasis" filter.

I use the DPA low-boost grids this way and adjust from that response as my baseline.  The high-boost grids have a more substantial peak and fall off, which requires more careful EQ tuning for transparent compensation.  It's just easier for me to dial in the appropriate correction and more likely to be acceptable without correction using the low-boost grids, even when I need to add considerable gain up top.  The low-boost grids just get me closer to the response I want than the high-boost grids do.

Yes, you can use this technique to effectively lower the noise floor of your recording chain in the "pre-emphasis" region.  But it will not lower the noise floor of the environment in which you are recording.  IME, the noise of the recording environment will almost certainly swamp the noise floor of your recording chain, so it isn't likely to provide appreciable improvement for concert recording.  But if it's easier to get the results you want with the long high-boost grids, then go ahead and use them instead of the low-boost grids.

A  GUI EQ makes visual feedback on adjustment easier, but regardless of the interface, listen closely while dialing in the EQ corrections.
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stevetoney

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Re: theory: favoring high-boost caps on DPA (and similar) omnis
« Reply #2 on: March 24, 2015, 12:23:58 PM »
However, my recording peaks are always in the low and mid regions:
excess bass due to room gain, audience clapping/screaming, or even a mic impact (mine or the performer)

The "air" regions are barely present at all and are likely to get lost in the noise floor.  So, there should be more than enough headroom to accomodate the 10dB boost centered at 12kHz (looks like 0.707 Q) from the DPA graphs.
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Of course, the exact levels and widths can be tweaked accordingly in case of obstructions and such, and recordings typically benefit from good EQ anyways IMHO.
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Anyways I'll test this theory at upcoming shows to see if things are acceptable after post with high boost grids.

I only EQ via GUI (Audition 3.0) and to achieve a balanced sound based on what sounds right to me while I'm mastering my recordings.  That said, the copied statements from your OP resonated with me in that, the vast majority of my EQ efforts are presence adjustments of my recordings in the ohhh 2k to 10k frequency range (vintage schoeps capsules).  The results often make a significant difference to the quality of my recordings (to my ears), so I don't understand why anyone using high end gear would limit themselves to never doing any EQ in post.

I haven't prioritized whether to apply gain or EQ first in my workflow, since I haven't perceived any sound differences when doing my adjustments in post, but I also haven't put any thought into whether it makes any diference either, so it's possible that I've been doing it wrong.
« Last Edit: March 24, 2015, 12:30:42 PM by tonedeaf »

Offline Gutbucket

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Re: theory: favoring high-boost caps on DPA (and similar) omnis
« Reply #3 on: March 24, 2015, 12:38:11 PM »
I haven't prioritized whether to apply gain or EQ first in my workflow, since I haven't perceived any sound differences when doing my adjustments in post, but I also haven't put any thought into whether it makes any diference either, so it's possible that I've been doing it wrong.

Mostly an issue of good gain staging.  If doing both in the same DAW software instance, which is doing it's internal calculations in 32bit floating point math, it shouldn't matter which is done first.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

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Re: theory: favoring high-boost caps on DPA (and similar) omnis
« Reply #4 on: March 25, 2015, 04:41:17 AM »
Disclaimer: old-fashioned Linux sysadmin/programmer here :)

I prefer command-line tools because it's easier-to-document and repeat results.  I always write it down as a shell script or makefile so it's repeatable and checked into a version control system.

I'm also horrible at GUIs and get lost hunting for things.  I also have trouble controlling pointing devices; for lack of a better term, they feel too "analog" to me.

Gutbucket: right, the noise floor of the environment is usually higher.
I have had maybe 3 instances of acoustic shows where my levels were totally off (more than -30 dBFS) and the high-boost grids might've helped (if I had mics with high-boost grids at the time).

So as far as using the high-boost grids go, I think it's best as insurance when:
1) levels were too low
2) mics are too far away or placed behind an obstruction

I don't think using high-boost would be useful if I nail the levels or could always ensure great positioning.  But I tend to err on the conservative side with levels they can do any damage there.

Also, I'm far too clumsy to attempt swapping grids while setting up at a venue, and I'm even worried about slipping and damaging my mics at home if I swap grids too often, so I'll be leaving the high boost ones on.

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Re: theory: favoring high-boost caps on DPA (and similar) omnis
« Reply #5 on: March 25, 2015, 10:00:32 AM »
All sounds reasonable.

If recording very quiet acoustic ambiances and nature sounds, this could be useful to effectively reduce the microphone's self-noise in the boost region by a few dB after you make the inverse EQ the compensation.  In practical terms, that would apply to the other 406X models more than the 4060, which is a few dB quieter than the other less sensitive versions- by about the same amount as this would achieve probably, but across the full spectrum rather than just in the boost region.  The boost region in which the grids are effective is a bit higher in frequency than the ear's most sensitive region, so this would only partly be effective as a noise reduction technique. 

I had hopes the high-boost grids would be useful in some situations, but unless making the required EQ compensation, my music recordings using them were always less acceptable than those using the low-boost grids, so I just keep the low boost grids on there all the time. 

BTW, in a pinch you can convert a high-boost grid into a low-boost one by first popping out the screen with a chopstick, then sanding down the screen end of the plastic barrel until it is the same length as a low-boost grid.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

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Re: theory: favoring high-boost caps on DPA (and similar) omnis
« Reply #6 on: April 22, 2015, 06:52:57 AM »
BTW, in a pinch you can convert a high-boost grid into a low-boost one by first popping out the screen with a chopstick, then sanding down the screen end of the plastic barrel until it is the same length as a low-boost grid.

Heh, think that'll work the other way?  I got a nasty soft-boost grid with a mic off eBay that already has a lot of paint on the sides of the grille.  Maybe I'll add a little more paint/goo and it'll become a high-boost grid :D

 

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