Propagation, amplitude, frequency and timbre are all sound principles that we need to understand as they relate to music production. Most of these principles can also be related to our everyday lives and how we listen, communicate and interact with others. In many cases people are oblivious to the theory behind important concepts that relate to sound and its production – however as music producers we need to have a firm understanding of these concepts and what it means for music production. To do this we shall take a closer look at sound, propagation, amplitude, frequency and timbre.
Sound is a disturbance of the atmosphere that humans and other living creatures can hear. Humans typically hear sound frequencies between approximately 20 Hz and 20,000 Hz. Other species have different hearing ranges. We have developed culture and technology (such as music, radio, phones and computers) that allows us to generate, record, transmit, and broadcast sound. As we are learning about music production it’s important to have a good understanding of different concepts relating to sound.
Sound propagates or moves through various media such as the air, concrete, brick, wood, water etc. Because of the different densities and make up of these media – sound moves through them at different speeds. During propagation sound waves can be reflected, refracted, or attenuated by the medium.
Sound propagation through air can be altered slightly by factors such as elevation, temperature and humidity. However, generally speaking sound travels at 340 meters per second or one mile in five seconds.
Propagation and Music Production
In music production it is useful to understand the propagation and reflection of sound as it relates to the recording studio or space. The sound moves through the space and reflects of different surfaces which affects its speed. When we are recording and mixing we can create a sense of space via the room and how it propagates.
Certain sound effects such as delay, reverb, phasers and flangers also relate to the concept of propagation and how sound moves.
Amplitude relates to the sound wave. It shows the size of the sound vibration, and this determines how loud the sound is. High amplitude makes a louder sound. This differs from the term ‘loudness’ which is our perception of sound related to duration and frequency.
There are many types of waves and in air the direction of the vibration is parallel. This is similar to the direction of propagation.
As the air compresses and rarefies it takes the form of a longitudinal wave. Amplitude is the extent of compression and refraction of the wave in the air. As they are hard to present – longitudinal wave are diagramed as transverse.
Amplitude and Music Production
Amplitude is measured in decibels. There are many places in our production sound flow where we can measure amplitude. In air it is Decibels of Sound Pressure Level, or dBSPL – zero being the quietest and going up as the sound gets louder. In the computer it is measured with the dBFS or Full Scale – zero being the loudest and goes down from there. Therefore it’s good to know the context of decibels when discussing amplitude.
When we are mixing tracks amplitude is important as we control it in relation to the amplitude and panning of other tracks. The goal is to get a pleasing mix of the different amplitude levels of tracks.
When producing music dynamic plugins help to controlling the amplitude of sound signals over time. These include expanders, gates, compressors, and limiters.
The ‘dynamic range’ of your recording equipment is also related to amplitude. For example this can show the range of decibels in which the piece will reproduce the sound properly – ranging from the noise floor to the distortion point.
Amplitude can also be important when setting up equipment – setting mic levels and setting output levels etc.
Frequency & Timbre
Frequency is the speed of the sound vibration, and this determines our sense of the pitch of the sound. Frequency relates to computer measurement and pitch relates to our perception.
Low frequency has slow moving pulses, high frequency has fast moving pulses.
It’s possible to have a low frequency and high amplitude sound – the frequency and amplitude are not correlated to the propagation rate – they are independent of each other.
This is important as certain audio effects really impact only certain parts of sound – and relates not so much to frequency but rather to timbre which is the collection of sound in multiple frequencies.
Simple sounds such as the sine wave have single frequencies – but most sounds have multiple frequencies and include harmonics (also known as overtones and partials).
Frequency & Timbre in Music Production
Audio effects that controls frequency and timbre includes equalizers and filters. These are used to raise and lower different frequencies and manipulate the timbre.
As mentioned earlier the range of human hearing frequencies is 20 hertz to 20,000 hertz. Females and children tend to hear higher frequencies better and we all lose hearing in the high end as we grow older. We also don’t hear equally across the range. This can be shown graphically as a ‘frequency response curve’. Recording gear and microphones also have frequency response curves to show how they act across the spectrum.
Another example relating to frequency is – the note A above Middle C has a frequency of 440 Hz. It is often used as a reference frequency for tuning musical instruments.
Sound Principles and Music Production
Our understanding of sound related principles such as propagation, amplitude, frequency and timbre are very important to our understanding of music production concepts. We have looked at the theory behind these principles and related them to their relevance in the field of music production. Understanding these sound concepts will give and the building blocks we need to explore more advanced ideas and techniques in the field of music production.