Scientists Explain: electric keyboards

Since the debut of electric keyboards, there has been a steady march towards improving the realism of the sound they produce.

This would often be done by recording better samples from a better acoustic piano, with more microphones, for example. In the last decade however, with the increasing power of computers, other methods for synthesising music are becoming available.

To understand the advances, let’s take a momentary trip back in time, say a few hundred years to understand acoustic pianos.
Pianos have a large number of strings held under tension inside their cases and when you strike a key a small hammer continues this motion and hits a string. This sudden impulse excites waves in the strings which eventually make it to your ears, where your brain steps in and converts these oscillations into a melodious sound.

The oscillations in any individual string are in no way simple, with many different types of wave happening at once. This is why simply recording samples of pianos or other instruments ultimately fails in the endeavor to produce a realistic sound.

Now that we understand how the sound of a piano is really a system of vibrating strings, we may begin to exploit this nature. Using the maths of Fourier analysis we can see all the different waves oscillating on a piano string, just by analysing the final wave. Combined with the physics of vibrations on a string, this data allows us to recreate a real piano sound. These mathematical and physical tools allow the electronic keyboard’s computers to know what key was struck, and how hard, and to calculate how the string resonates as a result.

The interaction between strings themselves may also be modelled. The computer is now capable of telling you how this modelled piano will respond to any key strikes. Converting the oscillations of the piano system to a pressure wave in the air, will then give you a simulated piano sound.

This method for sound simulation is known as physical modelling, and as computers become more powerful it is becoming very competitive. One of its direct benefits over the conventional sample-based sound is that by not requiring sound files, it takes up much less storage. The computational parameters may also be fine-tuned to your own liking – I’ve had the pleasure of playing a simulated 10 metre tall upright piano!

If you’d like to have a play, Roland keyboards incorporate this technology in most of their modern keyboards, and Pianoteq offers standalone software for PC, Linux and Mac.

If this article has got you interested in the Science of Music then why not attend IATL’s Music and Science meeting day on the 6th of May?Go to  http://www2.warwick.ac.uk/fac/sci/physics/news/physicsdays/events/musicandscience/ to find out more

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