Tone (or timbre in French) is the quality of sound that is left when you take away its pitch and loudness. The tone of a particular voice helps you pick it out in a crowd and know how they are feeling. The closer you get to the speaker, the clearer the tone of their voice becomes, providing a sense of intimacy. Over time as you listen and observe musicians you learn to identify the instruments they play by the tones they produce. Many instruments can play Middle C, but each one plays it with a different tone.
As your experience grows you may become aware of the variations in tone of different models of the same type of instrument, for example, different brands of acoustic guitars, which are affected by the types of wood used, the design of construction, and gauge and age of strings.
Languages evolve to suit the needs of the people who use them. The Inuit-Yupik peoples in Alaska have many words to describe different types of snow and ice. The Sami in northern parts of Scandinavia and Russia may have as many as 1,000 words for types of reindeer, words that would have no counterpart in a language spoken in a tropical climate where snow and reindeer don’t exist. While school children get by with the primary colors in their set of crayons, painters learn to identify a wide range of shades. There are over 16 million different color combinations available on the Internet that can be achieved by combining different amounts of red, green, and blue light.
Consumers who know how to adjust the bass and treble controls on their stereo systems may not be able to explain what tone is. Musicians and their teachers work intuitively with it as to shape their sound and use words like warm, dull, brittle, clear, breathy and bright to describe it, but the controls that go into modifying tone are often subtle or internal and therefore invisible to listeners. Audio engineers are the ones ultimately responsible for tone in music production and have the richest vocabulary, including descriptions like boomy, muddy, tubby, thick, hollow, dirty, edgy, and tinny.
The problem with using words to describe tone is that they are not precise enough to describe it and mean different things to different people. When we say “Don’t use that tone of voice with me!” we probably couldn’t explain exactly what that tone of voice is should the other person ask. Tone is not something that we normally work with, so we don’t have an adequate vocabulary to describe it that everyone is familiar with. That’s not a problem, because tone doesn’t come up very often in daily conversation. However, we will need a more objective language if we want to communicate with other engineers or machines.
The science of acoustics provides the mathematical precision of the help us precisely describe tone. Computer recording systems can analyze the tone of a sound and display it graphically and provide processing tools that engineers can apply in response to what they are hearing and seeing on the screen.
The sounds we hear in the world are a complex combination of different vibration patterns. Sound starts out as a pressure wave sent out from a vibrating object that causes air molecules to be pushed together and pulled apart as it passes through them. A waveform is a graph of the change in air pressure of air molecules in a particular place over time.
A graph of a sound’s spectrum (plural spectra) shows the frequency and amplitude of the sine wave components that it is made from. In the graph of a spectrum the vertical axis represents amplitude, as it does in the graph of a waveform. The horizontal graph in a waveform graph represents time, in the spectrum graph it represents frequency. The horizontal position of each vertical line indicates the frequency of that component, and the height of the line is proportional to that sine wave’s amplitude. Higher frequency (treble) components are on the right, lower frequency (bass) components are on the left. Babies start out able to hear frequencies from approximately 20 Hz – 20 KHz. Later in life they may lose some sensitivity in part of their upper range depending on their genes, age, and exposure to noise.
Frequency response charts show how well microphones and other devices respond to or reproduce frequencies. Dips and peaks in the graph show how some frequencies are not picked up well or are boosted. Calling a frequency response "flat" means that it doesn't have significant dips and peaks and is more accurate.
This graph of the pickup pattern of a Shure SM57 dynamic microphone shows that it does not pick up as well below 100Hz, and that there is a boost in the midrange before dropping off in the higher frequencies. The frequency boost can be desireable, as it gives more presence in that part of the spectrum. This microphone is a favorite for snare drum, whose fundamental frequency is in the 150Hz to 250Hz range, where the frequency response is flat.
Microphones that are designed to respond as well to sound coming from all directions are called omnidirectional. Omnidirectional microphones are good for recording a group of instruments together, or for capturing the overall sound from a sound source with a complex radiation pattern, like a piano that sounds different over the surface of its soundboard.
Microphones that pick up better form the front than the sides and back are called directional (often referred to as cardioid) microphones. These microphones are the best choice when you want to pick up one instrument out of a group, or to reduce the amplified sound of a singer circulating from a loudspeaker back into their microphone which can cause screeching feedback.
You are probably familiar with graphs plotted on the Cartesian plane using x- and y-coordinates. Another way to plot data is with polar graphs which use angles and distance from the origin. Polar graphs are ideal for ploting how well microphones pick up signals from different angles.
Read the article on Harmony Central that explains polar patterns and the three main types of directional reponse—omnidirectional, cardioid, and figure-8.
The Proximity Effect
The "proximity effect" is a boost in bass frequencies that occurs when a mic with a cardioid pickup pattern is located very close to the sound source. Some microphones and mixers have bass roll-off switches to compensate for this artifical emphasis. Some singers enjoy the effect and intentionally use it to change the tone of their voices.
Multiple pattern
Some microphones have switchable patterns, allowing you tochange from cardioid to omni depending on your application.
There are some acoustic treatment products designed to work with microphones and stands that are covered in this unit.
Wind screens and pop filters
Windscreens protect microphones from wind and explosive bursts of air, humidity, and spit from vocalists mouths.
A pop filter is often used when recording a vocalist in the studio. It protects the microphone from bursts of air (such as in the consonants "b" and "p"), humidity, and spit. They are fairly transparent acoustically.
Wind screens more convenient in live sound situations and are usually made from foam and fit snugly over the microphone. Many hand held microphones such as the Shure SM58 have internal windscreens to protect the micophone element. They dampen higher frequencies more than pop filters.
Microphone Construction
Dynamic microphones
Changes in voltage are induced by dynamic microphones from the motion of a conducting wire wrapped around the diaphragm that moves within a magnetic field. The mass in the voice coil is relatively slow to respond to changes in air pressure compared with condenser microphones, so it does not pick up low-energy high-frequency vibrations in the air. On the other hand, they are less expensive and more rugged and stand up to rougher treatment on stage.
Condenser Microphones
Condenser microphones have moving thin diaphragms placed close to a fixed back plate. The two surfaces have opposite electrical charges, and as the moving diaphragm vibrates closer to and further away from the back plate, a weak electrical signal in response to the changes in capacitance between them. Condenser microphones can be solid state or have tubes.
Unlike with dynamic microphones, power is needed to charge the two surfaces and amplify the weak signal. This can come from a battery in the microphone itself, from a nearby power supply, or coming back through the microphone cable from the pre amp, a system known as "phantom power".
Diaphragm size
Large diaphragm microphones are popular in the studio. Diaphragms are in the .75–1 inch diameter range.
Small diaphragm microphones (< .5" diameter) have very precise response since the small diaphragm responds well to low-amplitude high-frequency frequencies. They are excellent choices for acoustic guitar or hi-hat or other instruments with a lot of transients and overtones. They also have the advantage of being small and easier to fit in tight spaces.
Ribbon Microphones
Ribbon microphones have a small ribbon that is suspended in a strong magnetic field that responds to changes in air pressure and produce a warm sound. They are very delicate, and can be damaged even by the wind that is created by moving them around, or the ribbon stretched by not storing the microphone properly. Some ribbon microphones can be damaged by phantom power.
Applications
There are a variety of types of microphones designed for different applications.
Instrument Microphones
Vocal Microphones
Handheld
Wireless
From Musician's Friend buying guide: "The signal is transmitted using radio frequencies. The most common wireless systems use digital, UHF, or VHF frequencies. Affordable wireless mic systems that deliver good sound and bang for the buck typically use the UHF band. The best systems use digital technology that optimizes audio quality while also eliminating noise and signal dropouts that can be an issue with low-quality systems. Interference generated by devices such as radios, wireless phones, garage-door openers, and even fluorescent light fixtures are detected and eliminated by such digital circuitry.
Another way better-quality wireless mic systems deal with reception problems is through diversity technology. Receivers that have what is referred to as true diversity contain two separate radio modules, each connected to its own antenna. When interference is detected, a circuit compares the signal received by each module/antenna and uses whichever one is cleanest.
It’s important to note that receiver microphone frequencies must match. This is not an issue when you purchase a full system since the frequencies have been matched by the manufacturer. But if you are buying microphones and receivers separately, be sure they operate on the same bandwidths.
Wireless vocal mics come in a number of formats including hand-held models, clip-on lavalier mics, and headworn mics that have a headband. Some manufacturers also produce plug-in transmitters with which you can convert a standard wired mic to wireless operation."
Headworn
Piano Microphones
Surface Microphones
USB Microphones
USB microphones connect directly to a computer without requiring a preamp or audio interface. This makes them very convenient for recording podcasts and quick jobs.
There are many different heights for stands, and adjustable lengths of booms. Get quality stands that will last for a long time. Cheap ones are hard to adjust and tighten.
Microphones can be plugged into vocal processors to alter the sound before it reaches the mixing console or PA system. Effects include reverb, harmony, stereo effects, loops, and pitch correction. The effects can be engaged with a foot pedal for hands-free use, and presets set up to offer instant choices. Often a guitar or keyboard signal can be plugged in which the effect analyzes to determine what chord is in effect so the proper harmonies can be applied.
InSync article p. 295 on "How to Start Your Mic Locker". Make a list of any microphones you own, and a create a budget for how you can extend your collection. What kind of music do you want to record? Do you have any live sound needs? What are your priorities? What is your budget? Does your room need treatment? What stands do you need? What is your timeline and plan for acquiring the microphones you need? One approach is to take on some sort of job to get started purchasing the equipment you need to do professional work, and then finance subsequent purchases from payment received from clients while you are building your experience, rather than trying to buy everything all at once.
Microphones emit low level signals that need to be boosted by a preamplifier before being sampled or processed. Preamps can be found as dedicated units, and built into audio interfaces and mixers.
[ Week 5 ]
