Field Recordings: City Junkyard Part 2

In May I returned to the junkyard behind the city gravel pit and made some more recordings. The huge petrol tanks I spoke of in my previous post weren't nearly as overgrown and I was able to investigate them further.

The petrol tanks, from the side.

In one end of the larger tank, I discovered a perforation that allowed me to slip the Zoom H1 digital recorder inside. The end of the tank being essentially a ten-foot sheet of metal, simply rapping on it with my knuckle was enough to set off an immense reverberation within. The microphones were able to capture the sound far more readily through the perforation. It also had the effect of filtering out some of the constant noise from the MDF plant. The plentiful birdsong, on the other hand, was accentuated.

Tech notes: upon reviewing my recordings, there was an exceptional amount of low frequency rumble from this tank. It was easily scrubbed by applying a High-Pass Filter at 129Hz. I kept some alternate takes with the HPF set at 96Hz, which sound much bigger but not as clean. A lot of the MDF plant's shenanigans is in that very low band.

The larger tank, you can just see the perforation in the shadow to the left.

By climbing on top of the 'smaller' tank I discovered an open hatch. The cover of this was still attached, and could be prised up slightly in order to clash against the lip and create more interesting reverberations. I was able to lower the Zoom right into the tank in this case. I did this free-hand at first, but quickly attached a strap in case of droppage. I wouldn't have been able to retrieve it if I'd let go!

The hatch. Apologies for the cropping - I was using my telephoto lens.

In the bottom of the tank is about a foot of liquid - I hesitate to call it water - organic matter that's fallen in, decayed and mixed with rainwater and whatever chemical residues remain from its petrol-holding days. Regardless, it was perfect for dropping small pebbles into and recording the results. I even recorded a couple of 'aaahs' into the bargain.

Tech notes: these recordings required some subtle noise-reduction as well as the HPF treatment. I found that the pebble drops leaned towards the higher end of the audio spectrum, so weren't negatively affected as much by the HPF as the other sounds.

The pipes. Most are metal, but you can see a couple of plastic/polymer ones in the upper left.

I also revisited the large pipes I recorded last time around. This time I placed the recorder inside and clapped my hands into them. It creates a much louder percussion and echo than my metal striker. I had better results if my hands were also inside the pipe.

The pipes are approx 18" in diameter, with walls an inch thick.

Tech notes: I recorded claps from both ends of the pipe: the one with the Zoom inside, and from the opposite. Those from the opposite end turned out more interesting. The plastic pipe had a richer sound, while the metal one had a more complex echo. Just the sound of my voice, annotating my recordings, came out sounding all 'muzzy' from the peculiar acoustic properties of the pipe interior. Some of it was low-frequency rumble, but I can't be sure how much was to do with the Zoom sitting in the pipe without something to dampen the vibration. These recordings all clipped, despite turning down the recording level, but a little cheating in post-production did wonders.

The view down one of the plastic pipes. Overexposed to show the interior walls.

A fun day out if ever there was one. No doubt you'll be hearing these sounds in future productions!

Field Recordings: City Junkyard

As I've mentioned in previous posts, I take a Zoom H1 digital recorder with me pretty much everywhere I go. My job often presents opportunities to record all sorts of interesting sounds. I also have an affinity for junkyards, and waste places where junk accumulates, and seek these out in my free time. They also offer up photo opportunities, and a lot of my album artwork is shot in these locations.

This summer I was able to visit a site that was new to me: the city junkyard, which is hidden from prying eyes behind the city gravel pit. This is home to anything the City Works dept. doesn't have room for in their yard: lengths of various sized pipe and culvert, pieces of machinery and equipment that are obsolete or 'in reserve,' temporary signage posts, old electrical boxes, pumps, dump-trucks in various states of disrepair, giant petrol tanks (the kind usually buried beneath petrol stations), and miscellaneous other odds and ends. It all adds up into junk heaven for someone like me.

One of many electrical boxes left to the elements.

I spent a couple of hours going from one end to the other with my camera, digital recorder, and my trusty striker: a valve rod from a car engine. I mostly concerned myself with the various lengths of pipe, many of them over a foot in diameter. One of the coolest sounds I captured was throwing pebbles into the largest of these. The giant petrol tanks were also a source of impressive sounds.

Pipes!

I found that placing the microphone in the mouth of the pipes yielded the most interesting results: it picked up the optimum amount of reverberation. The mic placed in front, a foot or so distant, gives a subtler effect, and above merely accentuates the sound of the striker.

More pipes!

Among the iron/steel pipes were some of comparable size made of thick plastic. These produced good pinging echoes. If you've ever tapped on an irrigation pipe you'll know what I mean. They're somewhat tricky to record at a decent volume, so more experimenting is in order!

The end of the larger petrol tank. Both were largely obscured by brush.

A little about the petrol tanks. There are two at this particular location, and both, as far as I could tell, were sealed - which is a shame, because there's one at another location I frequent that has a gaping hole in the side, turning it into an excellent reverb chamber. So, I wasn't sure if my recordings would pick up the tremendous reverb that results from hitting one. The sounds resulting from holding the mic near the end and striking it weren't all that impressive. I had better results micing the space between the two tanks, which are cylindrical and lie side by side. But the best sounds by far resulted from micing the 2" threaded pipe that leads into the tank (and lets the sound ouuut!).

Part of both tanks can be seen in this pic.

One downside to this location as a source of audio recordings is that it's situated next to an MDF plant, which produces a constant low rumble. Its frequency is such that when I scrub it from the audio it strips more of the lower frequencies away than is ideal. It's a constant battle to preserve as much of the original sound as possible while making it clean enough to be usable.

Field Recordings, Part 2

Here's part two of my article on field recordings - part one of which can be found in the archive. This will give you an idea how much work goes into preparing the sounds I've collected for use in audio projects.

Once I have the raw recordings transferred from the Zoom H1 to my hard drive, it's time to edit them. Because I record a lot of sounds these days, I've made it a habit to announce what I'm recording at the beginning of each file. Before I started doing this I had trouble keeping track - especially if I didn't get around to editing files right away.


Step 1: I load the raw file into Sound Forge, my audio-editor of choice. I then trim the ends a tiny bit to remove the click noises produced by the Zoom's record button. When recording, I take special care to make sure the audio doesn't 'peak' (a techy term for overloading the mic, resulting in a distorted recording). As a result, the raw recording is often very quiet. So I normalise (increase the volume of) the file to 98% (2% below 0db or maximum).

Step 2: I remove any rumble from the recording if it requires it. Some of the lower bass frequencies can muddy a recording, so as a rule of thumb I EQ out anything below 80hz, which is about as low as the human ear can hear. If there's traffic noise in the background or particularly troublesome bass frequencies I'll go as high as 225hz. Mild wind noise can sometimes be scrubbed out in this manner too.

Step 3: Dynamics/compression. Oftentimes with digital recording the sound you capture is but a shadow of what was heard at the time. Compression allows an increase in volume while preventing the high peaks (the parts of the sound that have hit the 98% volume ceiling) from distorting. It also lifts subtleties such as ringing sustains, reverb, etc... that are naturally present but too quiet to discern in the recording's raw state. The downside to this process is it makes the background noise louder as well. But luckily there's a secret weapon to deal with that in step 4. Compression works best for very loud sounds, such as metallic objects being struck. Softer sounds, such as birdsong and streams, etc... are usually left as-is.


Step 4: Noise reduction. Once I have my file optimised for volume, it's time to scrub out some of the annoying background noise. I use a program called Goldwave for this. Its noise reduction filter allows you to feed in a sample of the unwanted background noise and magically scrub those frequencies from the recording. It requires some restraint, though, because being heavy-handed with this feature can harm the recording rather than improve it. I listen carefully to each file and adjust the settings to reach a natural-sounding balance. In some cases I'll apply a preset called 'gentle hiss/rumble reduction' if noise reduction affects the sound too much. Unless the sound is too problematic to clean (in which case I fall back on some extra EQ or discard it) the end result is a nice clean-sounding file.

Step 5: The final step is to load the cleaned file back into Sound Forge for final editing. I cut out parts of the file that have microphone or wind noise, or other unwanted sounds that haven't been completely removed by the scrubbing process. This is also when I cut files containing multiple takes into single pieces or 'one-shots.' These can then be used as-is, or loaded into a sampler and played as an instrument.

I've worked with these techniques on and off over the years, but this is the first year I've combined them as an archival process. I'm learning things all the time about how certain sounds respond: how much compression to use here, and how much noise-reduction to use there. There's still no substitute for capturing the cleanest sound possible in the first place, but when you're at the mercy of a noise-polluted environment or a sudden gust of wind, a little software can do wonders.

Field Recordings, Part 1

Not a lot to report at the moment. I've been engaged in the tedious work of cleaning up the backlog of field recordings made over the spring and summer so that they're ready for use in the Tales Audio Drama, music, etc... So I thought I'd write a post about what that involves, what kind of sounds I've been collecting, and how I go about it.

I've made my own field recordings and collected 'found sounds' for years now, mainly for use in music. I started out capturing them with a mini-cassette recorder, which I still have floating around the studio somewhere - it's good for achieving a phone-like effect on spoken word samples. Eventually, though, I saw the need for stepping up the quality, so I switched to a Sony MZ-NH700 minidisc recorder. This served me well for many years, but many a recording was ruined by the sound of the motor on the thing, which kicked-in every few minutes to write data to the disc.

Now there are a host of pocket-sized digital recorders available that offer 16 to 24 bit stereo recording with no moving parts, and after much deliberation I settled on the Zoom H1. I've had it since the beginning of the year, and have found it to be invaluable. I use it with a specialised 'wind-screen' outdoors, and also have a custom-made hydrophone I use with it for underwater recordings.



I take the Zoom with me pretty much everywhere. My job as a renovator gives me access to some interesting places, such as industrial buildings, and I live in a semi-rural environment with plenty of hiking trails. Unfortunately said trails are not far from mill yards, the main highway, and the train station, so there's an ever-present layer of noise pollution in the background at varying degrees. Most of this can be scrubbed out, or at least dampened - something I'll cover in Part 2. But certain sounds are particularly stubborn. I've learned to avoid making any recordings if a lawnmower can be heard, for example. Another trick is finding natural noise dampeners, such as a hill or bank between you and the unwanted noise.

On my hikes, once or twice a week, I keep in mind some of the sounds I need for my production and make use of what I find at hand. I needed the sound of trees being destroyed, for instance, and was able to find several trees ranging from saplings to much larger ones that had blown over or fallen from the weight of last year's snow. These could be easily lifted and let drop to achieve the effect.

As well as these kinds of engineered sounds, I've recorded the likes of streams, birdsong, and squirrels. I've recorded extensive metallic sounds in a junk-yard in the middle of the woods (this was a very lucky find!), and rock and gravel noises in two different quarries. On one occasion I was even caught in a thunderstorm with the Zoom to hand. Bliss!

The one problem with this undertaking is that sounds are relatively easy to capture; they pile up, a bit like digital photographs, in no time at all. But editing and archiving them is a long and drawn-out process. I'll take you through the editing stage in Part 2.