Sound is the centre point of everything we do. Every track, every part, every song is just a collection of different kinds of sound. But what actually is it? How does it work? And what are the fundamentals we should all know?
What is Sound?
To put it as plainly as possible, sound is a form of vibrational energy that travels through a medium. These vibrations are generated when an object moves and disturbs the air molecules around it.
A great way to visualise this is to think of an acoustic guitar, you pluck a string (the moving object), which sends vibrations through the air (our medium), and those vibrations move outwards until they reach our ears. Our ears then convert those vibrations into an electrical signal that moves to our brain, and are interpreted as sound.
Every single sound created or heard has the following characteristics;
Frequency: The frequency of a sound refers to how many cycles per second within that vibration. The lower the number of cycles, the lower the sound is perceived, and the higher the number of cycles, the higher the sound (hiss). The number of cycles is sometimes referred to as cycles, but is more often referred to as hertz, or as it is often written Hz. Generally speaking, the range of human hearing is often said to be around 20Hz-20kHz (20,000 Hz), but this number is affected by age, health, injury, and/or lifestyle.
Amplitude: The amplitude of the sound describes how much air (assuming air is your medium) pressure is in the wave. This pertains to how loud a sound is for the most part, and low-amplitude sounds have less air pressure and are quieter. Whereas those with higher amplitude have more air pressure and are louder.
It is often measured in decibels or dB. But for more on decibels, keep on reading until the end.
Wavelength: The wavelength of a sound describes how long the cycle of that sound is before it repeats itself. Normally, lower frequency sounds have a considerably longer wavelength (1Hz is roughly 343 metres), whereas Higher frequency sounds have considerably shorter ones (20kHz being roughly 1.7cm). The wavelength can be measured in any unit that can measure length, but it’s often measured in Feet (ft) and Inches (In), or Metres (M), depending on geographic location.
Speed: The speed of sound measures how fast the sound is moving throughout its medium. It is generally measured in metres per second or m/s. For most calculations, we refer to the speed as sound as 343 m/s, which assumes that the medium is air, and that it is roughly ‘room temperature’ around 20 Celsius. This is affected by temperature, and sound does move quicker in warmer places and more slowly in colder ones. It can also move much quicker or slowly through different densities of medium, for example, sound moves much quicker through water, as roughly 1481 m/s at room temperature.
Type: Sound waves also fall into two distinct categories: Periodic, which describes more musical sounds, and aperiodic, which describes sounds better described as noise.
The Decibel.
Sound is more often than not measured in decibels or dB, a logarithmic scale named after Alexander Graham Bell, which measures the relative change in two levels of sound, the sound itself, and a reference point.
Logarithmic scales can often throw people off. The first thing you need to remember is that it is a non-linear scale, so the correlation between numbers is often ignored. It would make sense that 2dB is twice as loud as 1dB, but that isn’t the case. This is further made confusing by the introduction of our ears and how they perceive sound. There are two numbers to always remember: 3 dB and 10 dB.
A 3dB increase doubles the intensity of the sound (or the power), but in terms of actual perceived loudness, it only equates to a noticeable difference in how loud it is, not a doubling.
A 10dB increase represents a tenfold increase in sound intensity, but also translates to a doubling of perceived volume. So 80 dB is twice as loud as 70dB, for example.
Types of Decibel
In practice, there are many different types of decibels that we use in production, including;
Decibels (A Weighted) or dBA is a scale that takes into consideration how human hearing works. It begins with 0dBA as the lowest threshold of human hearing, and tops out at 194dBA, which is where sound waves become shock waves. This scale is often used in everyday situations where people describe how loud a sound is. For example, if you see an advert for a vacuum cleaner, and it describes it as being say 70 dB, they are generally referring to dBa.
Decibel (voltage), or dBV, is a measure of signal voltage within an audio circuit. The reference point for the dBV scale is that 1 dBV is the same as 1 volt RMS. This scale is mostly used in consumer audio products, as well as some line-level equipment. You may often see equipment where the ‘line level’ has some sort of choice between -10 or +4; the -10 in this situation is referring to -10 dBV.
Decibels (Voltage, Unloaded) or dBu, is also a measure of voltage through an audio signal, but this time with no impedance load. The reference point used in this scale is that 0 dBu is the equivalent of 0.775 volts RMS. This scale is mostly used in professional analogue audio equipment, and the standard line-level signal is measured at +4 dBu.
Decibel (Full Scale) or dBFS is a scale used to measure digital audio signal levels. The reference point of 0 dBFS is the maximum level that digital audio can go before clipping. That makes 0 dBFS the ceiling of this scale. This means that we are mainly dealing with negative numbers. This is mostly used within Digital Audio Workstations and when dealing with other digital audio applications.
Once we can start to understand the basics of sound, we can start to better understand how minor and major changes during recording, mixing, and mastering can change things. But while understanding the basics of sound is great, we do need to dive a little more into the Ear itself, how it works, and how sometimes they aren’t as honest as we would hope. Check back soon for the next part of Production:101 – The Ear.
