Have you ever seen sound? Unless you’re one of a small percentage who experience chromesthesia, the answer is probably no. But you’ve likely seen sound represented graphically in a histogram. It’s a common and useful way of displaying information about sound, but it is not what sound looks like.
Sound is wave of varying pressure, compressing and decompressing at a rate our ears can detect. If we could see it, it would look more like ripples in water, only they’re in the air and moving right at you! I like to picture the energy bursts in the superhero movie Push. It’s helpful now and then to break out of the “sound looks like this graph” mentality and try to visualize what’s actually happening. Picture sound radiating out from a vibrating source, rippling through the air on its way to your ears.
A histogram may not be what sound looks like, but it does a fantastic job of representing two primary aspects: frequency and amplitude.
Frequency is the rate at which sound pressure varies. It’s measured in cycles per second which we call Hertz (Hz). Humans can hear frequencies as low as 20 Hz and as high as 20,000 Hz. Let’s all thank the French for the metric system, because we can refer to 1000 Hz as 1 kHz (kilohertz) and save ourselves a bunch of zeroes. In common “sound guy speak” a kilohertz is simply a “k” and a hertz is a “__”. We say things like “cut the vocal at 2.5k” or “boost 50 on the kick drum”. It’s assumed we’re talking about frequencies here.
Amplitude is the size or power of a wave. When talking about sound we call it sound pressure level (SPL) and measure it in decibels (dB). Decibels are a logarithmic unit where a difference of +3 dB is equal to approximately twice the power. For example, if a system uses 1000 watts to generate 100 dB, it will need 2000 watts to produce 103 dB. And this +3 dB change is barely perceptible to most people! Your church’s back row audio consultants may use subjective terms like “volume” or “loudness” and express their preferences in percentages – don’t correct them! Just nod your head and pretend to turn it down. The truth is, even scientific measurements like SPL don’t tell the whole story. An energetic but non-offending mix has as much to do with the balance of frequencies as it does the overall SPL. And yes, maybe the electric guitars really are five percent too loud (and sound like they’re “in a tin can” – but that’s another post!)
Sound is acoustical energy – pressure waves in the air, but sound equipment works with it as electricity. How do we turn sound into electricity to get it into our consoles? And how do we turn it back into sound? In both cases the answer is transducers. A transducer changes energy from one form to another. A microphone is a transducer that converts air pressure into electrical impulses. An under-saddle acoustic guitar pickup works on the mechanical pressure of vibrating strings. An electric guitar pickup senses a changing magnetic field which is why it only works with metal strings. On the other end of the system, a speaker turns electrical impulses into sound impulses. In fact, a speaker is essentially the same technology as a dynamic microphone. A sensitive pair of headphones can be used as a microphone – and a stereo microphone at that! (It’s a fun experiment but I wouldn’t try it live!)
Sound is not knobs and faders. It’s not the graphs we use to represent it. Understanding how sound works can connect us back to what we’re actually doing. However you represent it in your mind, remember that sound is always heard, not seen.