Before you read on, I feel I should give you the ‘Audio Geek’ alert, as this post has some techno babble 🙂 It is an experimental idea that I have for removing traffic noise from nature sounds.
The UK has some great natural landscapes to explore. As an auditory person I find nature sounds amazing, but our brain is brilliant at blocking sounds from our conscious awareness when our thoughts are elsewhere. Many of us tend to spend time day dreaming and thinking about many things at once, such as, what we’re doing later, what we need from the shops, paying a bill etc.
When I hear the wondrous natural sounds, such as the birds, insects, waterfalls, streams, I have a desire to record these sounds for the purpose of sound effects for use in Foley situations or in products that require nature sounds.
Here’s the problem, while I feel I am a competent sound engineer it seems that recording nature sounds has a few major drawbacks.
Firstly, the sound our ears hear in magnificent detail is seemingly lost in recordings. I find that the recorded ambiance never matches up to the real life situation. Why? Honestly, I am not totally sure but I think it is to do with current limitations of recorders and microphones compared to the ability of human ears and the brain.
Research tells us that our brain interprets sounds in three dimensions and can identify spatial details and can also interpret time / speed to some extent.
A police car rushing towards you with its siren on can be understood by the ears / brain thanks to the natural phenomenon of Doppler shift. This makes the siren sound (from the listeners perspective) increase in pitch as the car comes towards you and decrease in pitch as it drives away. Your ears can easily detect the variation in pitch, but your brain enables you to understand whether the police car is coming towards you or driving away by creating the multidimensional soundscape in your mind. We can even gauge how long it might take to come into view based on multiple environmental factors that the brain computes unconsciously at incredible speed.
Put simply this is the way we know that something is behind us, far away or close, over to our right / left, or when a sound is coming from above or below because the brain can make sense of the tiny differences in the vibrations that our ears receive. These sound waves operate in a 3 dimensional space and your brain calculates information based on the position of your ears in relation to the sound sources. A stereo recording cannot do 3 dimensional in this sense.
We have our own auditory surround sound system thanks to the mechanical vibrations of our ear drums and awesome capability of our brain to make perfect sense of this.
Man is the biggest problem
Recording technology just isn’t able to replicate multispectral three dimensional sound at this point in time.
But there is an even bigger issue facing the nature sound recordist, and that is the man-made environment.
Whenever you find a spot and press record there always seems to be some form of background noise, whether it be a dog barking, a cyclist, cars driving by, motorway noise, an aeroplane flying overhead, trains, wind turbines, people talking, mobile phones, loud music etc.
While in everyday life these usually blend in and we don’t notice them as much, they always seem more prominent in a nature recording. Removing this unwanted background noise is easier said than done.
The most common problem I have had is distant road hum or rumble.
Does karaoke hold the answer?
There is a sound engineer’s trick for removing / lowering vocals in a song sufficiently so that you can sing over it karaoke style.
I won’t go into too much detail but simply put, creating a mono version of the song by creating a split stereo version and reversing the phase of one side, strips out any mono elements that are centrally pan’d. Typically, the main vocals are centre of the mix and therefore, vocals will be removed or lowered in volume. It is fair to say, the success rate of this varies from awful to passable depending on the mix of the original song.
You can read more about this karaoke trick here http://blog.mediamusicnow.co.uk/2012/12/13/removing-vocals-from-music%E2%80%A6-is-it-possible/
How does this fit in with nature sound effects you may ask?
As mentioned earlier, the UK has some great nature sounds and I often find that although the intermittent noises in nature recordings can be dealt with, the hum from nearby main roads is pretty much constantly there in the background.
So, I got to thinking of the karaoke trick and whether it would work effectively for removing road noise? Now, I have no idea if it would or not, or whether more experienced nature recordists have done this already or something else entirely.
My idea would work something like this, and at some point I will do this as an experiment and report back.
Basically, Recorder A is left recording whilst Recorder B is taken with me to record another part of the Welsh countryside. When I get to this place I record as normal. After the recording, I go back and collect Recorder A.
This means I have one version closer to the road (more traffic) and one further from the road (more nature),
In the studio I now reverse the phase of Recording A and mix it with Recording B. In theory it should cancel out the road noise. I guess a future experiment is needed to see if this does or doesn’t work.
Have you had any experience with this? It would be great to hear from you in the comments. If you are an audiophile I hope this got you thinking. If you are not an audiophile and are still reading, then great, you have just experienced a short time inside my head. 🙂
Thanks for reading.
As a former BBC mobile recordist, I could say a thing or two about ruddy traffic noise! We got round it with a directional mic and bass-cut, but of course that took away the delicious natural ambience.
Yes, phase cancellation can work: I actually use it to delete the 100 Hz pump hum of our household boiler while I record voice. The boiler is miked up and a feed taken to a phase adjuster box, then played through a tiny amp into a speaker behind the studio wall. It does work, and is stable, but only at the one frequency and I think that could be a sticking point outdoors with spaced mics. They’re not really hearing the same sound. But what a worthwhile experiment among the wonders of Pwll-y-gaseg Wood!
Greetings from a fellow sound-enthusiast! Your article was an interesting read and I look forward to hearing your results. I deal with this problem constantly with my own field recordings. I’ve relied, for several years now, on a piece of software called Goldwave, which includes a customizable noise-reduction filter that works on the principle of frequency carving. (There are other applications capable of this, of course). If you feed it an isolated sample of the particular noise you want to remove, and play around with the settings, you can get some good results. It’s *very* easy to end up with something that sounds like a bit-crushed mp3 if you’re heavy-handed with it. It works better for isolating percussive sounds (metallic clangs, and so forth) than for things like birdsong or rustling leaves.
I sometimes use it in combination with a band pass filter, but you end up losing a lot of the ‘airiness’ inherent to sounds in nature. I wouldn’t advise this method for scrubbing the sound of running water, either! If I’m keen to preserve as much of the natural sound of a recording as possible, I’ll simply use EQ or a low pass filter to remove rumble, anywhere from 80hz to 255hz in extreme cases. This works for traffic to an extent, but the trouble with traffic is its not always constant. There’s always some git that wants to rev his car at a crucial moment, for instance! 😉 Low-pass can also help remove the odd stray bit of ‘wind noise’ that intrudes on an otherwise clean recording. Cheers!