Capturing Sound Flashcards
Transduction
changing of one type of energy to another
microphone definition
a transducer that converts acoustic energy into electrical energy
loudspeaker definition
a transducer that converts the electrical energy into acoustic energy
Sequence of an Audio Signal Pathway (6)
- A sound source creates sound wave vibrations in the air
- The vibrations of the sound waves are picked up by a microphone
- microphone converts the vibrations into an electrical signal
- The electrical signal is processed
- The signal is sent to an output device
- An output device transduces the electrical signal into sound waves
Dynamic Microphone Construction (3)
- Coil of wire is attached to a diaphragm and placed in a permanent magnetic field
- As the diaphragm and coil assembly moves, it cuts across the magnetic lines of flux of the magnetic field, inducing a voltage onto the coil of wire
- voltage induced into the coil is proportional to the sound pressure and produces an electrical audio signal
Mic Level
a very low level signal only a few millivolts of electrical energy
Dynamic microphone characteristics (3)
- produce mic level signal
- do not require power
- economical, durable, and will handle high sound pressure levels
capacitor (3)
- two oppositely charged (polarized) conductors separated by an insulator
- an electric field exists between the two conductors
- The amount of potential charge (voltage) that is stored between the conductors will change depending upon the distance between the conductors, the surface area of the conductors, and the dielectric strength of the insulating material between the two conductors
Condenser microphone construction (6)
- a conductive diaphragm and a conductive backplate
- Air is used as the insulator to separate the diaphragm and backplate
- sound waves cause the diaphragm to move back and forth
- As the distance changes, the amount of charge stored between the diaphragm and backplate changes
- This change in capacitance produces an electrical audio signal at the output of the capsule
- a condenser microphone includes a preamplifier that amplifies the signal to a microphone level signal
phantom power
Voltage sent to a condenser microphone between about 15V and 48 V
Electret Microphones (3)
- a type of condenser microphone
- It has prepolarized material, called “electret,” which is applied to the microphone’s diaphragm or backplate
- This permanent charge eliminates the need for the higher voltage required for powering the typical condenser microphone, so it can be powered using small batteries and normal phantom power
Microphone Physical Design (6)
- Handheld
- Lavalier
- Gooseneck
- Surface Mount
- Integrated/Array
- Shotgun
Handheld Microphones (2)
- used mainly for speech or singing
- includes internal shock mounting to reduce handling noise
Boundary Microphones
mounted directly against a hard surface
Integrated/Array Microphones
include multiple microphone elements and signal processing for applications like web conferencing
Gooseneck Microphones
used most often on lecterns and conference tables
Shotgun Microphones
named for their physical shape, as well as their long and narrow polar pattern
Wearable Microphones
- lavalier is attached directly to clothing
- head microphone is a microphone that is attached to a small, thin boom and fitted around the ear
Microphone Polar Patterns (4)
Omnidirectional
Cardioid
Supercardioid
Bi-directional
Omnidirectional
Sound pickup uniform in all directions
Cardioid
Pickup from front only. Rejects sound coming from side, with most rejection at rear
Supercardioid
Narrower pickup than cardioids and greater rejection of ambient sound but has some pickup directly at rear
Bi-directional
Pickup equal in opposite directions with little or no pickup from sides
Microphone Sensitivity (2)
- If you expose two different types of microphones to an identical sound input level, a more sensitive microphone provides a higher electrical output than a less sensitive microphone.
- Condenser microphones are usually more sensitive than dynamic microphones.
Microphone Sensitivity Specifications
An example of a sensitivity specification may look like this:
-54.5 dBV/Pa
1 Pa = 94 dB SPL.
“Pa” refers to the Pascal and it is a unit of pressure. 1 Pascal is the equivalent of 94 dB SPL. In this example, if you were to put 94 dB SPL into the microphone, you would realize a -54.5 dBV electrical output signal.
Microphone Frequency Response
defines the microphone’s electrical output level over the audible frequency spectrum
Microphone Impedance (3)
- Impedance is the total opposition to current flow in an AC circuit.
- Microphones can fall into two categories based upon output impedance:
Low impedance – 200 ohms or less (some as high as 600 ohms)
High impedance – More than 25,000 ohms. - Professional microphones are low impedance microphones.
Wireless Microphones
use RF transmission in place of a microphone cable
Professional microphone cables
shielded twisted pair
shielded twisted pair
two insulated wires twisted with a shield wrapped around them
Audio Signal Levels (3)
Mic Level
Line Level
Loudspeaker Level
Mic Level Voltage
0.001 - 0.003 volts
Line Level (Professional) Voltage
1.23 volts
Line Level (Consumer) Voltage
0.316 volts
Loudspeaker Level Voltage
4 volts or more
Common Signal Level Adjustments (3)
Gain
Attenuation
Unity Gain
Gain
the electronic amplification of a signal.
Attenuation
signal level out is less than the signal in
Unity Gain
no change in gain
