On Location Limiter/Pre-amps for FX Booms

[Dustin Moore]

Hello, I record large scale fireworks displays for home video distribution
and I'm looking for some advice on maximizing the "tail" of ground
reverberations as well as retaining the high frequencies because there
are considerable whizzes and crackles. I'm usually hundreds of feet
from the source without a viable means to get in closer for practical/workload related reasons.

For the last two years I've been running an R-4 (non-pro), a
single point stereo condenser (AT-822) and a drum kit dynamic mic in the field. I usually mix the single point with one or two tracks of on-camera audio which always seems to have a nice level of compression. At one point
I also tried a shotgun pointed opposite the source to see if I could
maximize reflections on one track but it seemed like the shotgun
element was overloaded to easily by the impulse and I couldn't just
add it to the mix with post-compression handling the spike.
The dynamic proves to be mostly useless in practice, it only hears
the transient.

The timeconstant on the limiter in the R-4 is long enough that I get
noticable pumping after a big thump and I don't think I like that effect
in general. I think I want a really short time constant so that the pressure
wave is handled and that as soon as the mic element is functioning
again, I've got regular gain. The mic-preamps on the R-4 are not good,
in general, for my work as they are relatively noisy. I wish I could
afford to keep or rent one of those four channel sound devices rigs
but I don't think I can swing it.

So far the best recording I've ever made was when I had the single
point stereo/TCD-D8 just lying against a hard surface at the top of a
particular earthen grade. I think the hard surface happened to provide
"the right" reflection phasing situation to keep the impulse down and
the rumble up. The qualities of the ground between the fireworks and recording location has a very large effect on that recording.

I've carefully read the discussion on gunfire as well as a gamesutra on
the topic by a forum contributer. I'm not in a good position to edit
booms shot-by-shot as there are thousands of them so I need a mic
strategy that doesn't assume I can perform the level editing one would
do for a center piece FX sample. If there was a plugin that would
erase the transient completely and automatically that would get me
somewhere. It seems like I need to fix my problem before the A/D,
though really.

I see that sound devices mic-pres are recommended for the gun shot application. With a 100ms release time I think I would like something considerably shorter.

I'm thinking about getting an Apogee Mini-Me and using the full
soft limiter plus push it limiter to shape the peaks. It seems that one of
the compressor/limiter settings has a short time constant for drums
and I'm guessing that's shorter than 100ms. Does this seem like a
sane idea?

Also, is there stereo condenser mic solution (sub $1.2k) that is
particularly good with ridiculous transients while having good
sparkle in the highs? Is it worth thinking about a large diaphragm
dynamic like a PR 40?


On a totally different note, anyone know of a flash field recorder that
has a timer? I'd like to rig a rumble recorder from 2 miles away but
I need it to auto-on and record. I would be nice to set it up 4 hours
ahead of time and have it just "work."

The only other way I can figure that would get me a decent LFE track would be to build a thick masonry structure. At one location I had access to an 8x6x6 structure with solid walls 10" thick and that had a good rumble inside of it. Anywhere else though and the transient pulse kills the LF.

[Geert van den Berg]

Hi Dustin I took the liberty to move your thread to the location recording forum as you might get more answers there. I hope someone can help you out.

(I kept a redirect link in the post-pro forum)

[tnjazz]

On your "totally different note", the SD units have timers (702, 722, 744)

[Jungle Jazz]

I don't have any experience doing what you describe, so take this with a salt lick. Have you considered a stereo ribbon microphone? The Royers might be out of your price range, but Cascade makes a couple different stereo models for under $1.2k. Or maybe you could get a couple of Beyers and try a Mid/Side setup?

[Jim vanBergen]

I've recorded a LOT of fireworks for television broadcast.

I use many mics, with high speed (ast slew rate) preamps and really fast compressors. I compress each mic as well as the buss. I like to use dynamic omni microphones close to the firing range for LF content and condensers for HF content and each mic gets a major filter to shape the sound appropriately. If you have the mics near each other, make sure you are phase coherent or prepare for problems when you sum sources.

I think the Mini-Me with softlimit is a good step for a limited gear solution. I would NOT buy a stereo mic without doing a rental or demo first. IMO there are only three reasons to buy a stereo mic: 1) cost savings, 2) fixed pattern consistency; 3) ease of rigging. I like AEA stereo bars and the flexible K&M stereo bars.

As its out of doors, get a good windscreen. I often have the ability to put several pairs on the tops of roofs in major cities. I'm also miking audience response so I have many pairs in many places.

There is NO reason not to place mics close to the firing range. You and your gear need to be far away, but I have had RE-20s and Shure VP64s next to firing canisters, with me 300+ or more feet away. You need GOOD PREAMPS! The Apogee will also help with this problem. As far as the LF, have a solid filter to cut off the HF and thena good & FAST compressor on the mic doing that job. Squeeze the transient DOWN and capture the tail.

I hope these thoughts help!

JvB

[Dustin Moore]

Originally Posted by Jim vanBergen

I use many mics, with high speed (ast slew rate) preamps and really fast compressors. I compress each mic as well as the buss. I like to use dynamic omni microphones close to the firing range for LF content and condensers for HF content and each mic gets a major filter to shape the sound appropriately. If you have the mics near each other, make sure you are phase coherent or prepare for problems when you sum sources.

Thanks for the response!

Yeah, I spend a lot of time slipping tracks to bring the phases back into
acceptable alignment. I don't think I can swing having a full board with
busses/inserted compressors on location. Do I need to have a post
limiter compressor before the A/D or can I do it in post? This rig must
run off battery power for four hours straight 5 days in a row so any I
can put off to post is worth its weight in lead acid batteries. I know
the best rig for this would probably consist of two stereo preamps
($3k) and two stereo compressors ($1.5k) and a 18inch rack. That's
a bit much for me at the moment.

If I do a Fostex FR-2 or a Mini-Me I can get two channels with
acceptable limiting. Are there any of those upper-level cheap
multi-channel rigs like the Focusrite saphire series or the RME firefaces
that have decent analog limiters after a fast preamp? I think I already
know the answer ("HAHA, no way, get out the checkbook etc...").

How does one recognize a "fast" preamp anyway? I can't find slew
rates for most of these boxes. I would assume mv per millisecond or something would be the units.

[Jim vanBergen]

Originally Posted by Dustin Moore

Do I need to have a post
limiter compressor before the A/D or can I do it in post?

Are there any of those upper-level cheap multi-channel rigs like the Focusrite saphire series or the RME firefaces that have decent analog limiters after a fast preamp? I think I already know the answer ("HAHA, no way, get out the checkbook etc...").

How does one recognize a "fast" preamp anyway? I can't find slew
rates for most of these boxes. I would assume mv per millisecond or something would be the units.

Hey Dustin,

- you can of course use the buss comp in post- whats important is not clipping any individual path; from the preamp to the individual tracks that are being recorded to any buss. I always have one, because I am ALWAYS mixing a 2-mix for air or edit/post reference; Apologies for being obtuse with that; my only point is NO OVERS!

-some upper-level cheap multi units have limiters. IMO they are sonically one step above a pile of dog poo unless you REALLY have to use them, don't. I have two different types of this kind of 8-ch preamp, a Preonus Digimax and a Focusrite Octopre; I bought these for larger recording sessions for bands who have 6-20 tracks of keys or playback, and tried them on key inputs as well, then sent them back to tracks and keyboard recording. I think the Octopre is mildly better in the land of sonic dog poo, but I personally would not use them as a "good" limiter. On the other hand, ya gotta start somewhere, and you might try renting one to see how well it does. The Preonus has a big wall wart that is a pain but the focusrite I think uses an IEC cable- things you will have to consider for a four hour recording. I'd look at the Apogee MINI-series and the Grace Lunatec as a starting point for good battery-powered preamps.

-Slew rate is basically the rise time for the amplifier in the preamp; slew rates are considered "fast" when they are looking at V/mS. Vintage slew rates are about .776 V/second while fast slew rates go from 14V/microsecond and up in designs that I like; I 've seen specs as high as 140V/mS, but I don't know if I have heard a major difference going from "ultra-fast versus good and fast". There is a big difference from vintage/slow to fastm for sure. The better preamps DO publish the spec, as it has a noticeable increase in high frequency response & attack and an accurate bottom end, both likely to be desireable for fireworks recording.

I think this situation is subject to the good, fast, cheap triangle- you can only ever have two of the three.

I hope this helps!!!

JvB

[huub]

sound devices mm1 preamp ($350)works a couple of hours on 2 aa batteries, or a day or more on an external np-1 battery, has a built in limiter, is supersmall, and sounds fantastic, I'm sure it's good enough for classical even..
mp1 is even cheaper, but has no possiblity of np-1 battery..
As long as your a/d doesn't clip, I see no reason to not do the comp/limiting in post..