This is, because “pure pitch” is produced only by a sine wave. Every acoustic signal, be it a voice or any instrument creates not only one, but multiple waves through the air.
Those are a combination of the “fundamental” and the “overtones”. The fundamental is generated by the fundamental vibration's frequency, hence the name, the overtones by “partial” vibrations.
How those are generated we'll cover later, or to be more precise all the time. “All the time?”, you might ask. Indeed.
The thing you'll need to keep in mind is, that the amplitudes of the different overtones, also called harmonics, and their ratio give every instrument it's recognisable voice.
How the instrument sounds, therefore depends on the overtones generated and those amplified. So basically, all we will be dealing with is those overtones.
If you caught yourself thinking “I thought there's more to it”, let me assure you, there are loads of factors contributing to this overtone production and amplification.
For example; your playing technique! A lot is in your fingers and you can experience that first hand, so I'm giving you a bit of a “homework”. Don't worry, no protocols needed, though I'd like to hear about the experience you had.
My assignment to you is the following; pick up a guitar - preferably an acoustic - and play it with your fingers and then with the pick. Only play one string open at a time and move your finger or pick from the closest you can get to the bridge up to the 12thfret, then continue to the first fret.
Try every string, or at least the low E, the D, the g and the high e string.
If you're playing an electric, change the pickup and repeat the whole procedure. Oh, and make sure to do it on a clean channel with all amp settings at a neutral level.
Then repeat the whole exercise, with your fingers or pick at a different angle towards the string and towards the body. Ever tried having your fingers angled towards the bridge and the thumb stretched towards the fretboard or being angled in the thumb’s direction? Ever tried striking the string with the pick being hold “diagonally” towards it, at an 60° angle?
My advice would be to take your time and try as much as possible. This way you can learn a lot about your guitar's sonic capabilities. And do it slowly, concentrated, noticing how the tone changes.
For now, I will not explain to you, why this change occurs. It would be unscientific, since this is a perception-experiment partially and my explanation could, through the built-up of expectation change your perception.
So for now, that's all about it. I hope, that I got you interested at least a bit and you'll be back for the next part, where I'll be talking about some more fundamentals, why the exercise you should do changes the tone and also sound qualities.
Should you have any questions or suggestions or be feeling like writing down your experience to hand in your “homework”, feel encouraged to drop me a few lines in the comments section.
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