Rob from Sonata HiFi

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Sometimes, when things seem to be getting overly complicated and you really can’t see the wood for the trees, I’ve always felt the best thing to do is revert back to first principles or look to the KISS acronym (Keep It Simple, Stupid).

This is especially true when looking at sound, which is essentially a simple construct in theory but one that can quickly become very complex in the real world.

Basically, as mentioned in my previous blog, a sound wave is produced by a source of energy that causes a movement of molecules in matter – solid, liquid or gas.

The displacement of the air molecules results in pressure changes, an increase in pressure as the molecules are squeezed together (Compression) or a decrease in pressure as they are pulled apart (Rarefaction)

More energy produces a larger movement of molecules and a greater pressure change, which can be seen as an increase in the Amplitude of the resultant sound wave and heard as a louder sound.

Think, pump up the volume!

In its simplest form, we can illustrate a sound as a sine wave plot of amplitude (air pressure) changing over time, and the length of time it takes to complete this sound wave cycle is referred to as its Period.

A sound wave is simply two things – Amplitude and Time

The number of sound wave cycles that occur in a second of time is defined as its Frequency (measured in Hertz, Hz), something that we can hear as changes in Pitch…. Julie Andrews and Do-Re-Mi-Fa-So-La-Ti-Do come to mind!

Generally, the human ear can respond to a range of frequencies, from a low of 20 wave cycles per second (20Hz) up to a high of 20 thousand cycles per second (20,000Hz or 20kHz)

So far, so simple…. But things are about to get a lot more complicated.

Unfortunately, in our natural world, a pure tone composed of a single sine wave frequency does not exist and all of the sounds that we hear are known as complex sounds that are composed of multiple different frequencies.

These additional frequencies give a sound its own unique character, referred to as its Timbre.

That’s why, when you hear the same musical note (for example ‘Concert A’ at 440Hz) being played on different types of instruments such as a Flute, Piano, Trumpet or Guitar, you can differentiate between each type of instrument.

This is because, even though the most prominent frequency that each instrument produces is an ‘A’ (440Hz), known as the Fundamental, they also produce a different series of other frequencies (known as Harmonics or Overtones) at various levels to create their individual Timbre.

Interestingly, we can produce a sonic fingerprint for every individual sound by doing something known as a Fourier Analysis. This breaks down any complex sound into its individual sine wave frequencies and the various amplitude levels of those component sounds.

However, the frequency spectrum of a note played on a piano for instance will be composed of hundreds of sounds, not just the basic harmonic overtones from the string but also the unique resonances within the instrument that results from hitting a single key.

Differences in construction, materials and design help to create the classic sound characteristic of various manufacturers, that’s why the sonic fingerprint of a Steinway piano is different to that of a Bosendorfer or a Fazioli.

Being able to capture those amazingly complex sounds and recreate them in a lifelike manner is an incredibly difficult task, as I shall discuss in future articles.