In this second and final article I will discuss microphone patterns, recording device pre amp settings, editing and the final mastering phase of this collection. Before I dive into all the technical mumbo jumbo I want to express that when I’m setting up and actually recording thunder and lightning I get quite excited. There must be something in the air, alien mind control beams or just the anticipation of getting the “ultimate” thunder clap or lightning strike. It’s very hard work and involves exercise, listening, tracking the storms and watching the skies. I feel like a kid in a candy shop and I feel the recording is the easy part. So, now we begin.

Part 2: The Real Work Begins.

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The Microphones and Other Gear
Only recently have I been recording with my Sennheiser MKH-8040ST XY and ORTF microphone sets at the same time during the storms. Before I moved to my current location I did not have a very suitable area to set up both Sennheiser MKH-8040ST rigs. I did use them both together occasionally at my previous location but they could only be pointed in the same general direction to be protected from the rain and wind. Now I have a location that allows me to have each rig pointed in any direction I want them to be. I also have the opposite side of the house which has a few protected areas to place one of the MKH-8040ST rigs or a Sony PCM D100. Most of the time I just place the D-100 on the other side of the house as a back up which has saved my bacon a few times. I can quickly get the PCM D-100 rolling before I set up the other microphones if I’m caught off guard with a unexpected storm.

There are two things I really love about using both the narrow XY and the wider ORTF patterns. First, the same thunder event recorded by both microphones can sound very different from one another even though they are located in the same general area fairly close together. With one of the microphone sets pointed West and the other East I can capture two sides of the storm. One captures the approaching storm front while the other captures the exiting of the storm. Even though most thunder claps are primarily omnidirectional, these two setups record very different aspects of the claps. The ORTF, if pointed slightly away from the approaching storm captures a wonderfully rich and spacious stereo image. This wonderfully wide ORTF stereo image also captures the side to side echoes off the mountains here and when combined with the narrower XY stereo image the recording can be collapsed down just a bit without losing it’s wide character. The XY stereo microphone adds a wealth of “center” information that really makes the composite thunder sound deep and huge.

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Thunder in North Idaho sounds really incredible, very different than the city or urban areas. The lightning strike transient is reflecting off the mountains, the lake and the surrounding forested hills and it can reverberate for a very long time. Depending on how far way the strike is makes a huge difference in the soundscape generated. Closer strikes tend to have a mid-range quality to them while still having lots of weight to them and the distant claps swirl and reflect for a very long period time, panning left to right. The extremely close up strikes have an amazing sharp attack quality the them and then boom like crazy after the initial strike. The XY is great to have because it’s more focused in the center but still have a very nice stereo image that sums to mono nicely for LFE effects with that 10Hz thump.

Second, I take comfort in the fact I can set one of the recorders preamps a few dB lower than the other. Thunder has an amazing dynamic range and I’ve noticed 20dB swings in volume going into the recorders from one thunder or lightning strike to next while recording. Having the recorders at different input levels has worked well many times. Clipping can and will occur if the levels are not set properly and that’s what I want to discuss next.

How Loud Can it Get?
Loud… Extremely loud with massive amounts of low end frequencies being produced that can overwhelm the microphone element or recording device preamp. This has happened to me quite a few times. A thunder clap will begin at nice, medium volume and then suddenly the trailing echo gets very loud and boomy as it ripples back off the distant mountain ranges. I tend to be a little cautious with my input levels and set them a slightly lower than normal. I have never figured out what part of the recording chain is getting overloaded, the microphone or the Sound Devices recorder preamps. It sounds like clicks but has a subtle distortion also. The limiters on the recorders engage but the level never gets close to 0dB on the meters. Strange. Maybe it’s the frequency response of the Sennheiser MKH-8040 which is very wide and can go as low as 10Hz. This low frequency energy may be responsible.

iZotope’s RX4 Advanced to the rescue! This audio application can perform magic on any file that has overloads or clicks. I would prefer not to use it but it has come to my aid many times with the digital clicks and other minor glitches that can occur during recording. There have been a few times that a lightning strike has been so close to the microphones that a tiny electrical voltage “click” is created at or just before the start of the lightning strike. I’m not sure what it is, but I can only assume it’s the lightning bolt electrical charge being picked up by the condenser microphone elements.

How Long Can This Take?
I’ve recorded storms for over 3 hours at times and this can create a LOT of data at 24-Bit 96kHz when running 2 or 3 stereo recording devices. Out of these hours of recordings there may be only a minute or two of usable thunder sounds. Since I tend to focus on making sure the microphones are OK outside in the storm, the levels are good and my iPad storm trackers are current I do not keep a written log while recording. Yes, I know it’s a bad habit but my main concern is just getting the take and making sure me and my gear are safe. I figure I can always find out what the good takes are later using Soundminer.

That’s what I do next and it can take a long time cataloging and organizing the recordings not because of no written logs but because the files are so long. I make my notes in Soundminer while auditioning and naming all the files. I can quickly jump around the timeline of the file to find the good stuff. Sometimes the good stuff is rain or wind. I seem to capture quite a bit of it during these storms. I separate the rain and wind out from the thunder takes if they are worthy. I then archive the wind and rain sounds for future editing. Once I have located all the good stuff I then archive all the files to two backup hard drives and rest a bit.

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Critical Listening, Processing & Mastering
The next phase of editing and mastering the sounds is a long and extremely focused experience. Before RX4 Advanced had RX Connect for Pro Tools I would weed out all the bad stuff in Soundminer and then create what I call “Raw Pre-Masters”. These files are the raw files with no filler and are the files I open in RX4 to work all the processes that need to be done before the final stage of loading them into Pro Tools for the final pass editing and mastering. This Pre-Master stage is very important. I listen very carefully to each file, sometimes in headphones, to find out what needs to be done to make it perfect. So many unwanted sounds can get into the recordings that it boggles my mind. From the tiniest rain clicks to ultra-sonic bats, birds, dogs, squirrels (I really hate them), cars, planes, tree branches, voices, you name it, it can get in there. I also check the file to see if it requires a noise reduction pass with RX4. I may perform up to five different de-noise passes, not over each other but to the raw file with different noise reduction settings to see which one sounds the best.

When performing the noise reduction pass I start with a 3-6dB broadband reduction and gently inch that number up, sometimes to 12dB or until I start hearing artifacts. The most important aspect of this stage is finding the perfect location in the sound file for getting the noise profile. I locate the longest section I can analyze and then preview with different reduction settings and other advanced parameters available in RX4. One such advanced setting is the balance between “musical noise” and “gating”. Most of the time I give priority to “gating” as it sounds better to my ears with the low end frequencies. I have been able to successfully remove wind, rain, hum and other broadband noise distractions with RX4.

Once I have a noise profile that works I perform the process and save that version as a new file. I then do the “get rid of the crappy noises” pass which may include de-clicking and spectral repair. Regarding spectral repair, I experiment with either lowering the gain of the offending noise or replacing it. Each type of process can bring very good results depending on what it’s trying to get rid of and synthesizing back in. This can take a really long time but when it’s done it’s so much cleaner sounding. I save that as a new file and it becomes the final “Pre-Master” candidate for Pro Tools.

After the files are loaded in Pro Tools I adjust and refine the file levels, equalization (if needed), fades and perform time based “Cut and Crossfade” edits if there is something RX4 cannot remove to my satisfaction. The longer storms that have thunder claps with long sections of just rain or wind between them are edited together with attention paid to making sure the resulting audio file sounds natural. I usually work on the sounds from the specific date the storm happened at one time. I don’t time warp around and work on files from 2012 while working on files recorded in 2014. This way I can make sure the files sound consistent and make sure the levels are optimal during the final pass. After all this fine tuning is complete I work the Metadata in Soundminer. I try and make sure the files are named and organized so they stay grouped by storm date or thunder type. Some storms yield just a couple of good claps and they may be just distant booms so they are organized by that type along with other files like them. The final task is to choose the files that will go into the final sound effects library release. Not all the files I work on end up in the final library. Some just don’t make the cut after I take a short break from the critical listening and editing. I allow them sit for a while and cook.

After all the recording and editing I’ve performed on this collection over the years I can finally sit back, relax and listen to all those wonderful storms without having to worry about getting hit by lightning.

There you have it, the making a thunderstorm library. I hope you enjoyed it. -Frank

To check out the library and for more information: Thunderstorm III HD Professional Sound Effects Collection

Some footage from a severe thunderstorm that roared in on 8-2-14 in North Idaho. The audio in the video is from the actual storm. Recorded with a pair of Sennheiser MKH-8040 stereo rigs. ORTF and XY were used along with a Sony PCM D-100 recorder that was setup in the front of the house with a Hero 2 camera. This storm produced extermely strong winds and knocked out power to 50,000+ people here.

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