Capture Of Sound Flashcards
What does a microphone do?
Converts variations in air pressure (sound) into electrical energy
How does a Dynamic Microphone work?
● Movable coil is positioned in a magnetic field, attached to a diaphragm
● Sound enters, diaphragm vibrates
● Coil moves in magnetic field, inducing a varying electric current
● Called Electromagnetic induction
What is a diaphragm?
A thin piece of material that moves in response to the changes in air pressure
How does a condenser microphone work?
● Contain a capacitor (two charged plates)
● Sound causes a plate to vibrate
● Change in separation causes a change in capacitance, so a current flows
How sensitive is a condenser microphone?
Quite sensitive - effective capture of quiet sounds
What are dynamic microphones like price-wise?
Generally inexpensive
What’s the frequency response of a condenser microphone like?
Flat and accurate
What features make dynamic microphones good for live use?
● Can withstand high SPL/volume
● Resistant to moisture
● Does not require phantom power
True or False, condenser microphones are able to capture a wide frequency range?
True
Do condenser microphones capture a brighter or darker signal than dynamic microphones?
Brighter
Why are dynamic microphones suitable for bass instruments?
Limited high frequency response
What can be said about the dynamic range of a condenser microphone?
It’s wide
What type of microphone is better for studio work, condenser or dynamic?
Condenser
How does a ribbon microphone work?
● Sound vibrations disturb metallic ribbon suspended in magnetic field.
● Voltage generated proportional to movement of ribbon.
What sound does a ribbon microphone produce as a close mic?
A warm sound - emphasises low frequencies
What does phantom power do to a ribbon microphone?
It damages or breaks it
What does a pre-amp do?
Converts a signal into a workable line level
On a pre-amp, what does the pad control do?
Attenuates the gain by a set amount to prevent clipping
What does a High Pass Filter do?
Removes frequencies below the cutoff frequency
What does the ‘Polarity’ control on a pre-amp do?
Inverts the polarity of the signal
What does a polar pattern do?
Describes how a microphone picks up sound from around the capsule
What does omnidirectional mean?
Picks up sound from all around the capsule
Describe the polar pattern of a cardioid
Rejects sound from behind the microphone
What is a cardioid microphone best for?
Close-mic work
Describe the polar pattern of a hypercardioid
Picks up sound from in front of the capsule and gives some capture of those behind
What is a hypercardioid microphone best at?
Providing partial isolation from other instruments but capturing some of the ambience of the room
Describe the polar pattern of a figure-of-8 microphone
Picks up sound from in front of and behind the capsule
What are Figure-of-8 microphones best at?
Mid-side recording techniques to give a stereo image of the sound
What 4 ways can engineers avoid capturing unwanted background noise and spill?
● Ensuring performers wear closed-back headphones
● Keeping the monitor mix relatively quiet in headphones
● Using acoustic screens/isolation booths
● Making use of overdubbing and directional microphones
What does frequency response mean?
The frequencies a microphone picks up
How do we know how ‘true’ the captured sound from a microphone is by its frequency response graph?
The flatter the graph, the more ‘true’ the sound is
What do peaks on a frequency response graph mean?
Those frequencies are captured louder than they are in real life
What does transient response mean?
How quickly the diaphragm can move when disturbed by a vibration
What type of microphone tend to have the fastest transient response
Small diaphragm condenser microphones as they have the lightest and easiest to move diaphragm
Why do dynamic microphones tend to have a slower transient response?
Because the diaphragm is connected to a heavy coil, so it doesn’t move as quickly
What will happen if the volume on an electric piano is set at a low level, and the audio interface gain is turned up to the maximum?
You will capture lots of hiss
Why is it important to record at a good level?
To maximise the signal-to-noise ratio, but not loud enough that the signal’s peaks are clipped
What is the signal-to-noise ratio?
The difference in volume between the signal you want to capture and the noise
What will a poor signal-to-noise ratio mean?
Noise is more prevalent in the recording
What is headroom?
The gap between the loudest peaks of your audio and the point at which digital clipping begins
What is analogue soft clipping sometimes used for?
Adding warmth
What does digital clipping sound like?
Harsh and unmusical
What does ‘Z’ represent on equipment?
Impedance
What are Lo-Z inputs normally used for?
Microphones
What are Hi-Z inputs normally used for?
Instruments such as electric guitar and bass guitar
What do DI boxes do?
Convert a signal at instrument level to microphone level
What is the order of signal levels, quietest to loudest?
Microphone, Instrument, Line
What will connecting a line level source to a microphone level input cause?
Distortion: the signal is louder than the input is designed to accept
What type of connectors do microphone level signals tend to travel through?
XLR
What connectors do line level signals tend to travel through?
Balanced TRS jack, or unbalanced phono
What is the proximity effect?
The increase of low frequencies depending on how close the microphone is to the sound source - the closer they are, the louder the low frequencies are
When is the proximity effect particularly apparent?
When recording male voices and acoustic guitars
When can the oriximity effect be used positively?
Fir recording kick drums and bass guitars
What can you do to reduce the proximity effect?
Use an EQ or High Pass Filter; Alter the microphone position, moving it further away
What can be used to remove unwanted low or high frequency noise?
Filters
What type of filters can be used to remove hiss?
Low Pass Filters
What type of filters can be used to remove hum?
High Pass Filters
What can be used to remove a specific frequency that is causing a problem?
A parametric EQ with a narrow Q
What does it mean if 2 sound waves are in phase?
Their peaks and troughs line up
What does waves being out of phase cause?
Destructive interference
In what situation must phase be considered?
Any situation where you are using lots of microphones to record the same sound source
In what situation is phase difference particularly problematic?
When you are recording using two microphones on opposite sides of a drum
What is the difference between phase and polarity?
Phase implies a shift in time relative to an initial wave, Polarity refers to the reversal of two connections on a cable
What does placing a microphone at different angles do?
Changes the range of frequencies that are captured
What will placing a microphone on-axis do?
Capture a brighter sound
What will placing a microphone off-axis do?
Capture a duller sound
What is the difference between an active and a passive DI box?
Active DI boxes require phantom power or a 9V battery, whereas passive DI boxes do not
What are plosive sounds?
Sounds with a strong initial transient (e.g. p, d)
What can you use to reduce the impact of plosive sounds?
Use a pop filter
How does a pop filter reduce plosive sounds?
By dispersing the air more evenly to avoid such a large and quick diaphragm movement
