Dealing with high intensity sounds is problematic. As we will explore in much more depth in the next part on firearms the experience of shockwaves has less to do with what you hear than the sensations you feel. Recordings of such intensity are rare because few microphones can handle the dynamic range. If you had a tape or digital recorder with you, when you listen to it back all you will hear are some distorted clicks.
All recordings of thunder you hear are from at least a kilometer from the lightning. When we make explosions and suchlike we have to use a lot of artistic licence because the real sounds just don't translate well into a recorded media. The lightning we are going to make next is what I call Scooby Doo lightning. It's actually closest approximation of the sound of distant sheet lightning which normally happens at high altitude as it moves across the sky.
Thunder is the sound of lightning so let's use the correct terms. What gives thunder it's interesting quality is the interaction with the environment. Much of what you hear are echoes from things like buildings on the ground, clouds and a process known as refraction.
The actual bang, or with sheet lightning multiple bangs, are amazingly short events, almost impulses, but they do have a tone.
The patch below attempts to emulate the essential features. Notice that the noise signal is overdriven and clipped. This markedly increases the amount of high frequency in it. The filters are attempting the resonance of a column of superheated air. In fact the filter values are chosen empirically while listening to the sound of a glass marble dropped on a tiled floor, a sound sample I have that is a very useful impulse to reference when making explosive noises.
Let's model this initial crackling sound. It is another process that has a natural relaxation, again we will talk about this more when we build the spark machine, but basically we want the time between each bang to take an increasingly longer time. If you think of the electricity stored in a great reservoir like a barrel of beer then as we get to the bottom it comes out with less and less pressure. The first crack of the lightning has the hardest job to do, it must ionise air oxygen and nitrogen and water molecules to form a conductive path.
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The secondary sparks which follow in the ion trails carry a bit less energy. So remembering that frequency content is related to energy we can assume the later crackles are a bit lower in frequency than the initial sharp one. You have seen this PureData formation before, a chain of delays. The order in which you make the connections is very important here, start with connecting the random units so that each [del] atom is loaded with a definite value before we start to propagate a bang message through the chain, finally connect all the delays moving left to right.
Each bang decrements a counter starting at 10, this value is used to derive both the center frequency of the noise bands and the decay time of the burst. We start with one short, sharp, bright "snap" and end on a long trailing noise burst of much lower energy. The sound that arrives after the direct signal comes from many sources and has much more in common with reverb than a plain series of echoes.
The Sound of Thunder, without the fear of strikes
In fact a great tip for music production is to use time compressed thunder as an impulse response for a reverb which works beautifully on vocals, but that's another story. In a reverberation the echoes we hear are no longer distinct, as they combine from different sources they phase and distort to produce a rumbling that undulates in volume and tone. We could create a really complex reverb. That would be dandy for an expensive film production but as usual we are going to paint with broad strokes and an emphasis on efficiency suitable for realtime clientside use. We will use a chunk of distorted brown noise to get this effect.
Sweeping the frequency range from about 30Hz down to 3Hz gets us the effect of the density thinning out, and bandpassing the whole thing though a Hz slot takes away the edginess of the clipping process to leave a nice mellow rumble. Not all waves travel at the same speed in real air.
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- xuxixutiqevy.gq: A Sound of Thunder.
Refraction is the effect where some frequencies travel faster than others, normally because of water in the air or because of temperature differences. If you have listened to a large outdoor PA at a rock concert from the very back of the stadium or festival you will have noticed that sometimes the wind or mist can turn the sound into a swirly soup.
The greater the distance the more noticeable this effect becomes. The lowest frequencies arrive later than the higher ones. Thunder which has travelled several kilometers to reach your ears demonstrates this quality very strongly. Sometimes there is as much as a few seconds difference between the arrival of the main bang and the boom containing bass frequencies.
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All these signals have travelled through the air but arrive in stages. This is subtly unlike the effect we consider with explosions next where some actually arrive first because they came through the ground. Air distorts the sounds in a storm because it's not uniform so our final deep rumble bears almost no relation to the other parts, it is in fact just a long slab of "black noise" significantly delayed from the rest of the sound.
So picture the entire effect now in terms of the noise colours. Starting with white, orange, then red speckles the initial attack is followed up with brown and finally black noise. Does this seem familiar? If you've animated explosions in visual media this sequence should make you think of the analogous process in which brief high energy bursts are followed by long after-effects of increasingly lower energy.
The Sound of Thunder, without the fear of strikes
The final cut below subpatches our three components for clarity. Thunder is a "one shot" effect like percussive drum noises in music. Once it's decayed away below an audible threshold we can shut off the entire DSP processing code to this effect to save CPU cycles.
Again the order of connections is quite important, the switch needs to receive a 1 value first of all before the bang triggers the other subpatches. In theory it makes no sound at all. Remember that propagation of sound in a gas is by longitudinal waves where local compression and rarefaction is down to the elasticity of the medium.
AskANerd: June 16, 1999
Certainly the air is moving a lot when it's windy, but these movements are in a single direction. If wind can be said to make a sound it is a super low frequency, measured in millihertz mHz and totally outside our hearing range. So why do we associate wind with a ghostly wailing noise? Not only that, but a rivalry is growing between the cruel, obsessive son who bears his name, and his elder, secret son, whom he cherishes deeply. The Boer War will take from Sean, in both blood and gold, but the conflict and its consequences will also offer him everything a man could want.
Sean must now decide: with both sons in his life, is he willing to pay the price he needs to keep them? Halaman terpilih Daftar Isi. Isi Chapter. Praise for Wilbur Smith Dedication. Chapter 1. Hak Cipta.
Talk:A Sound of Thunder - Wikipedia
The Roar of Thunder Wilbur A. Smith Tampilan cuplikan - His readership has built up over fifty-five years of writing. Born in Central Africa in , Wilbur became a full-time writer in following the success of When the Lion Feeds , and has since published over fourty global bestsellers, including the Courtney Series, the Ballantyne Series, the Egyptian Series, the Hector Cross Series and many successful standalone novels, all meticulously researched on his numerous expeditions worldwide.