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Acoustics The physics of sound In this article I will be discussing acoustics, what they are and what they involve. Acoustics is the science of sound and sound is something used in everyday life, it is how sound is created and how it travels. Sound is omnidirectional which means it travels in all directions in addition to just staying in one place. Psychoacoustics is how you perceive sound; we perceive sound as pressure fluctuations, which cause our eardrums to vibrate. Sound waves are a wave of compression and rarefaction, by which sound moves across a medium such as air, all sound is vibrations and all vibrations are is movement that is trying to regain its original position.
A waveform is a curve showing the shape of a wave at a given time. The energy of sound causes the air particles to ripples of layers of more dense (compression) and less dense (rarefaction) air molecules, with pressures different to the normal air pressure. The compression is where the wavelengths peak and the rarefactions are when the wavelength is at its trough. This is how you get your typical wave shape. Frequency is the amount of full cycles of compression and rarefactions in a
second, Sound is measured in Hertz (Hz) so the kick drum in the chart has a bottom depth of 60-‐80Hz and therefore will have 60-‐80 complete compressions and rarefactions in a second.
The Doppler effect is where there is a change in frequency and wavelength. When an ambulance or police car goes past, its siren is high-‐pitched as it comes towards you, and then as it goes away becomes low pitched. When a source moves towards an observer, the observed wavelength decreases and the frequency increases. When a source moves away from an observer, the observed wavelength increases and the frequency decreases.
The amplitude’s directly related to acoustic sound or is related to the intensity of a sound. Also amplitude is more specifically the degree of change positive or negative in the wavelength; high the compressions are and how low the rarefactions are.
Decibels are the measurement of the amplitude in sound, they are also relative to the observer meaning what could be 20db to one person could be 50db to another.
Envelopes in general are an important concept in synthesised music, because they are used to shape sounds in many ways, but the one most often encountered is the ADSR envelope.
The attack begins when the midi note is received, you can see in the diagram that this pad begins inaudible then rises so this pad starts quite quickly. The decay phase defines how long the note will take to reach a settled volume after hitting the attack peak. The volume is usually lower than the attack peak; since notes in natural instruments tend to “stab” in then fade in intensity a little. The sustain level is the volume at which the decay will finish and the note will be held at this volume until the MIDI key is released and the release is the fade of the note until its silent. The speed of sound is the distance travelled per unit of time by a sound wave propagating through an elastic medium. The speed of sound is 344 metres per second.
Phase is whenever 2 or more waveforms arrive at a single location out of phase; their signal levels can be combined to make amplitude of levels at that one point
in time. Whenever two waveforms have the same lengths and peak amplitude they will be completely in phase the new combined wavelength will have the same frequency, phase and shape but will have double the amplitude. If two wavelengths were combined with complete opposite waveforms then they would cancel each other out.
Harmonics are notes made in a special way, it’s a wave put over the basic fundamental wave which gives us musical octaves, For example, since concert A is 440 Hz (A3), the ear hears 880 Hz (A4) as being the next highest frequency that sounds most like concert A. The next related note above that will be 1760 Hz (A5). Therefore, 880 Hz is said to be one octave above 440 Hz, and 1760 Hz is said to be two octaves above 440 Hz, etc. harmonics are perceived as creating a sound that is pleasing to the ear, while odd harmonics will create a dissonant, harsher tone just sounding like noise.
The principles of musical instruments There are many different types of instruments all played in different and make unique sounds to that particular family of instruments.
Wind instruments produce sound by the vibrations of air, typically by the player blowing the instrument, the most commonly known wind instrument I would say is the trumpet. A trumpet is a brass instrument with a powerful tone consisting of a long metal tube looped once and ending in a flared bell and three valves for producing variation in pitch.
On a trumpet it is the metallic mouthpiece that produces the sound. There are various different mouthpiece shapes; a mouthpiece with a deep cup will produce a mellower sound, while a mouthpiece with a shallower cup will produce a bright, piercing sound. Mouthpieces are made of brass or silver and trumpeters choose a mouthpiece according to their personal preference. The structure of the trumpet enables the note to be lowered by one tone by pressing the first valve, by a semitone by pressing the second valve, and by one and a half tones by pressing the third valve. String instruments make sound with vibrating strings, and the pitch is modified by the thickness, tension, and length of the string. String instruments can be played in many ways, and come in many variations.
The violin is the smallest member of the string family. Sound is produced by drawing the bow across one of the four strings or by plucking the string with a finger; the bow uses horsehair or a synthetic material to vibrate the strings as it is drawn over the instrument. All string instruments produce sound in the same manner. The main differences are the sizes of the instruments and how high or low each instrument can sound. The parts of a violin are usually made from different types of wood, although electric violins may not be made of wood at all, since their sound may not be dependent on specific acoustic characteristics of the instrument's construction. Violins are usually strung with Perlon or other synthetic, or steel strings.
Percussion instruments produce sound when they are struck or shaken. Percussion instruments are made from many materials, but usually consist of either a solid material or a thin stretched material.
The snare drum has a crisp untuned sound that is used by the military and in marching bands or in the typical drum kit. Sometimes called the side drum, the snare drum has two heads made of skin stretched over a hollow metal frame. The top head is struck with wooden drumsticks, which creates a kind of rattling sound.
The xylophone consists of hardwood bars in graduated sizes set on a metal frame, this tuned instrument is struck by hard mallets to produce a bright, sharp sound; The timbre is complex because of the way it is tuned. With the larger,
lower sounding bars on the left, the notes of the xylophone are laid out much like a piano keyboard. Xylophone has a high sensitivity and a wide dynamic range and for a xylophone a typical frequency range is 392 -‐ 2090Hz. Because it has a sharp sound the attack is fast and the delay is fast leaving not much after sound.
A guitar a musical instrument that is held against the front of your body and that has usually six strings which are played with your fingers or with a pick.
A guitar has a large dynamic range however the classical guitar has a greater dynamic range than the steel string guitar and the frequency range of a guitar is 82-‐1397Hz. The envelope of a guitar is a very quick attack, not as fast as the attack but a fairly quick delay, a long sustain and a long release.
The piano is a musical instrument with a manual keyboard actuating hammers that strike wire strings, producing sounds that may be softened or sustained by means of pedals. It has a large dynamic range and the largest frequency range between 28-‐3951Hz. The envelope of a piano is a sharp fast attack, a short delay, and a long gradual sustain and a fairly fast and sharp release.
The mechanisms of human hearing
Hearing is the process by which humans use their ears to detect and perceive sounds. Ears are important for hearing and for controlling a sense of position and balance. Each ear is divided into three sections: The outer ear, the middle ear and the inner ear.
The outer ear consists of an auricle, auditory canal eardrum outer layer. The
auricle is Cartilage covered by skin placed on opposite sides of the head, the Auditory canal is also called the ear canal and the eardrum outer layer is also called the tympanic membrane. The outer part of the ear collects sound. Sound travels through the auricle and the auditory canal, a short tube that
ends at the eardrum. The middle ear includes an eardrum, cavity which is also called the tympanic cavity, ossicles which are 3 tiny bones that are attached-‐ malleus is the long handle attached to the eardrum, incus is the bridge bone between the malleus and the stapes and stapes which is the footplate; the smallest bone in the body. sound entering the outer ear travels through the middle ear and causes the eardrum and ossicles in the middle ear to vibrate. As it travels, it amplifies and changes from air to liquid. The inner ear includes an oval window which connects the middle ear with the inner ear, semi-‐circular ducts that are filled with fluid; attached to cochlea and nerves; and send information on balance and head position to the brain. The cochlea is a spiral shaped organ of hearing; it transforms sound into signals that get sent to the brain. The range of human hearing is generally considered to be 20 Hz to 20 kHz (decreasing to 16 kHz with age), but it is far more sensitive to sounds between 1 kHz and 4 kHz. 120 dB is the pain threshold and define the audible sound
frequency range as ending at about 20,000 Hz where the threshold of hearing and the threshold of pain meet. Psychoacoustics is essentially the study of the perception of sound. This includes how we listen, our psychological responses, and the physiological impact of music and sound on the human nervous system. The haas Effect is a Psychoacoustic Effect where our ears determine the position of a sound based on which ear perceives it first and its successive reflections that will give us the perception what direction the sound is coming from and how far away it is. The cocktail party effect refers to the ability of people to focus on a single talker or conversation in a noisy environment. For example, if you are talking to a friend at a noisy party, you are able to listen and understand what they are talking about and ignore what other people nearby are saying. Masking can be If someone listens to a soft and a loud sound at the same time, he or she may not hear the soft sound. The soft sound is masked by the loud sound. The loud sound has a greater masking effect if the soft sound lies within the same frequency range, but masking also occurs when the soft sound is outside the frequency range of the loud sound. Masking Beats The reason of the health and safety Noise Regulations is to ensure that workers' hearing is protected from very loud noise at their place of work, which could cause them to lose their hearing or to suffer from tinnitus, which is when you have permanent ringing in the ears. The law is if the workplace has a daily or weekly average exposure to 85 dB then there must be hearing protection and hearing protection zones, also workers must now be provided with information and training if the workplace is 80 dB and the limit is 87 dB.
Fletcher and Munson using headphones in1933 first measured equal-‐loudness contours. In their study, listeners were presented with pure tones at over 10 dB increments in stimulus intensity and at various frequencies. The listener was also presented with a reference tone at 1000 Hz For each frequency and intensity and the reference tone was adjusted until it was perceived to be of the same loudness as the test tone. Masking is where one sound is over powered by a sound that is louder, for instance if you are talking to someone and a truck drives past you may not be able to hear the person that is talking to you even though they are closer to you than the tuck.
There is different ways to protect our hearing when exposed to loud sounds; you can wear earplugs, which are inserted to block the ear canal. They may be foam or pre-‐moulded ones. You can also use Semi-‐insert earplugs, which consist of two earplugs held over the ends of the ear canal by a rigid headband. And finally you can wear Earmuffs, which often consist of sound-‐attenuating material, and soft ear cushions that fit around the ear and hard outer cups. A headband holds them together.
If you are working in a studio At the end of a recording session, return the studio to its original condition, disconnecting all microphones and extra patch bay cables, turning down all faders, turning off all phantom power on preamps, and properly wrapping and storing cables. You should treat the studio and equipment with care and consideration for others. Also most definitely No drinks, No food, alcohol, or tobacco may be used in the studio facilities.
The acoustic characteristics of spaces
Like any wave, a sound wave doesn't just stop when it reaches the end of the medium or when it encounters an obstacle in its path. a sound wave will undergo certain behaviours when it encounters the end of the medium or an
obstacle. Possible behaviors include reflection off the obstacle, diffraction around the obstacle, and transmission (accompanied by refraction) into the obstacle or new medium. Reflection of sound waves off of surfaces can lead to one of two phenomena -‐ an echo or a reverberation. A reverberation often occurs in a small room and Smooth walls have a tendency to direct sound waves in a specific direction. Diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path, and Diffraction of sound waves is commonly observed; we notice sound diffracting around corners or through door openings, allowing us to hear others who are speaking to us from adjacent rooms. Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. Sound proofing is almost essential in a music studio if you want noise escaping the room as little as possible, walls, ceilings and sometimes floors will need sound proofing and this can be done using sponge. The materials in the sound proof room absorb the sound so the sound doesn’t get out the room.