BASICS OF AUDIO
This audio program of the basics of audio is the first in the Audio Basics series of lectures. This lecture outlines the fundamentals of sound and its importance in music production work. The audio programs that follow will lend more detail to the topics outlined here.
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What Are The Basics Of Audio?
The basics of audio are the fundamental principles of what makes up sound and how it disperses in space. By understanding these basic principles, you can learn to make better decisions when recording, mixing or designing your studio.
Understanding the basics of audio will take away a majority of the guesswork that comes when recording and mixing. Most great productions happen by design, not by chance. When magical performances occur they are captured on a solid foundation of thinking and actions that preserve them well for others to enjoy.
What is Sound?
Sound is simply is a disturbance of molecules. These molecules can be air molecules or the molecules of solid objects. When any kind of event happens that takes these mediums away from their restful state and forces them to vibrate, you get a disturbance which is perceived as sound.
When a disturbance happens the molecules are compressed together and they shoot off in every direction from the point of disturbance. These disturbed molecules will bump into each other and spread out in compressed waves. In their wake they will leave an area where there are less molecules. Unless the disturbance is sustained, the particles will come back to a restful state. This is the elastic medium that is necessary for sound to exist.
Air happens to be very elastic medium and it's also very easy to disturb. A wall is much more rigid but also has some elasticity and can also transmit sound. If you strike a wall with a hammer the vibration will travel more quickly than in air because the molecules are so close together but It will also decay much faster because the material is more rigid.
Resonance, is a particular frequency range or area of frequencies that cause an object to sympathetically vibrate. The frequency or frequencies that an object vibrates at is determined by its basic physical properties and what is exciting it. Those frequencies, when tuned, can be perceived as pitch. This is the fundamental design principle of the creation and development of musical instruments.
Creating objects of different shapes and sizes that resonate the air in a pleasing way is the art of the instrument manufacturers. Creating acoustic environments that best show off the quality of those instruments is the art of acoustics. Capturing and manipulating those sounds is the art of music production and engineering. All these art forms are working with the same basics of audio principles.
Propagation of Sound
Among the most fundamental of basics of audio is the propagation of sound in a space. This is acoustics, the science of sound. An incredible amount of work has gone into quantifying and understanding acoustic principles.
These principles are used to design recording spaces, control rooms, concert halls, speakers, amplifiers and sound systems all with the purpose of making a balanced and pleasing listening environment. The design musical instruments and how they project in an acoustic space plays a huge role in the selection and placement of microphones to best capture the essence of that instrument.
How you manage and control the acoustic space, the instrument, and the microphones that capture them, is the most important part of recording. Understanding these basic principles, allows you make the best decisions.
When scientists work with sound they use terms that described the physical attributes of sound. Frequency, pitch, amplitude, wavelength and speed of sound are just a few. The following paragraphs outline these basics of audio terms.
The Sound Wave
What is a sound wave? Sound waves are similar to water waves. If you think of a wave in water, the start of the cycle would be the beginning of the first wave above the waterline, continue with a wake below the water line, and ending with the beginning of the next wave.The difference is that sound waves radiate in all directions, not just on a level surface like water waves do.
A sound wave is the completion of a compression and a rarefaction cycle. The compression part of the wave is a grouping of bunched up air molecules and is the similar to the wave above the waterline. Rarefaction is the separation of air particles like the wake that follows below the waterline. Sound waves, like water waves, repeat in succession with the later waves getting weaker and weaker as time progresses.
Frequency is the number of wave cycles that occur within a period of 1 second. Our hearing mechanisms are only capable of perceiving a frequency range of 20 cycles per second up to 20,000 cycles per second. This defines the lowest bass frequencies and highest treble frequencies we can perceive. The measurement term is called Hertz.
In reality, most people do not have the capability to perceive sound at this full range. Nor do most need to. The human voice occupies a range that is well within those limits. These are the frequencies we are most sensitive to because they define our ability to communicate though speech.
People who work with music and recording and really train their ears are able to keep this extended frequency response as long as they don't abuse their hearing mechanism. If subjected to loud or hurtful volumes on a consistent basis, those capabilities can be permanently lost.
Another basics of audio term is pitch. In general, most sounds transmit with a complex array of frequencies. When a particular frequency stands out it can take on a musical value that is defined as pitch. Pitch is the relative highness or lowness of a frequency. Relative to any pitch is a series of other pitches that would define musical scales, chords, etc…
Amplitude and Loudness
The next basics of audio term is amplitude. This term describes the loudness or softness of the sound that were listening to. Like the frequency range of our hearing we also have limitations on the loudest and softest sounds we can perceive.
Those limits are the threshold of hearing and the threshold of pain. The primary measurement for amplitude in an acoustic space is sound pressure level which is measured with a decibel scale. 0dB SPL is the loudest sound we are able to perceive accurately is 120 dB SPL.
Although we can hear at levels louder than 120 dB SPL, the sensation overexcites our hearing mechanism and causes a distortion that can permanently damage our hearing. 135dB SPL is considered the threshold of pain. 150 dB SPL would render you permanently deaf.
Wavelength and Speed of Sound
Wavelength and the speed of sound are basics of audio terms that are dependent on each other. The length of a given frequency wave is dependent on the speed at which the sound wave travels. The speed at which sound travels is dependent on the temperature where the sound wave is occurring.
Lower frequencies have a longer wavelengths. Higher frequencies have shorter wavelengths. This is determined by some simple math. Measure how far sound travels in 1 second and divide that distance by the number of cycles that occur in that same second.
Sound travels at a rate of 1130 feet per second at 70 degrees Fahrenheit. If you want to know the length of a 100 hertz sound wave, divide 100 into 1130 and you will get 11.3 feet. That is the distance it takes for a 100 hertz waveform to complete one compression and rarefaction cycle.
You can also use the same math to find what frequency is 10 feet long by dividing 10 feet into the speed of sound. 1130 divided by 10 equals 113 Hertz. This basic math is very important to the physical design of recording studios and the acoustic materials that are used to control those frequencies in a recording space.
The Perception of Sound
There are psychological aspects to sound as well as physical. While the psychological aspects are harder to measure, the study of these effects are critically important to the music producer and engineer.
The psychological and emotional aspects of sound are the reason why we listen to music in the first place. Understanding how sound affects feelings in the listener is an important part of getting the meaning of the song to translate to the listener.
DJs understand that consistent pulsing low frequencies within certain a certain range of tempos will keep people dancing. If you interrupt that tempo, low frequency pulse or rhythm for too long, people will leave the dance floor. Playing with those variations in a creative way, however, can add excitement to those participating.
Frequencies are not the only way convey emotions in music. A specific series of notes played by a clarinet may sound very harsh and annoying. The same series of notes played by a flute or an oboe may sound incredibly beautiful. These differences are hard to quantify in scientific terms and require the sensitivity of the composer, producer, engineer and musician.
The psychological aspects of sound will be different for each person, based on their own life experiences, likes, and dislikes. If you are studying music production or engineering, you must study the music people to listen and what makes them like or dislike it.
Most people's reaction to a song is instantaneous and unconscious. If you ask the average consumer to explain why they reacted a certain way, they won't be able to tell you. Study their physical reaction to a song and you will learn much more.
The following series of audio lectures break down the basics of audio concepts outlined here in more detail than can be conveyed on a written page. I hope you enjoy them and learn from these basics of audio principles to help you make better music and better music productions. Enjoy!!!
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Anatomy of the Ear
Protecting Your Hearing
Temporary Threshold Shift
Audio Ear Training
Physics of Sound
Fletcher and Munson
Speed of Sound and Wavelength
The Sound Envelope
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