Audio for Media Exam

Amplitude

intensity/height of the of the sound wave

Crest

Top part - amplitude can be calculated from central point to top

Through

Bottom part - amplitude can also be calculated from central point to bottom

Cycle

one completed repetition of the sound wave

Wave cycle

time necessary to complete a cycle

Frequency

number of completed cycles per second of a sound wave

• increased frequency —> higher pitch

• decreased frequency —> lower pitch

Timbre

character or quality of a voice/musical sound as distinct from its pitch and intensity

• volume and speed of frequency make up the timbre of a sound

Frequency people can hear

20 Hz - 20 kHz

Connectors

Mono

1 Channel (center)

• same signal goes to both speakers

Stereo

2 Channels (left & right)

• can reproduce left and right channels in 2 speakers

Setting Levels

identifying your setting levels help achieve a good recording

Mic level

Voltage of signal generated by a microphone

• travels through an XLR

• requires a preamp to boost the signal to line level

Instrument Level

Falls between mic and line level

• travel through a TS jack connection

• Also needs a preamp to get to line level

• “Inst” should always be connected when you connect an instrument to your interface

Line Level

Highest-level signal before amplification, used when connected any non-instrument devices

• travels through TRS jack connection

Speaker Level

reached by an amplifier just before the speakers

Important level rules

• Microphones need mic preamps directly after them

• Line or speaker level signal should NOT be sent into a mic preamp

• Signals must be at line level to be recorded

• Instrument level signals need a DI (direct injection) box to be recorded properly, or select Inst option in interface

• Speaker level signal is very high voltage signal, and should ONLY be fed to speakers

Recording devices - Line Check

ensuring all signals are reading their intended destinations

Clipping

Feeding your recording gear levels that are too high

—> leads to unwanted distortion

Analog

audio is represented as voltage that is continuous in time and level

• Analog Signals vary continuously

Digital

to digitize the signal you have to first convert the continuous voltage into a sequence of numbers with limited precision

• Digital Signals only have discrete values

Sampling and quantization

processes by which a continuous signal is digitized for subsequent digital signal processing

Sample rate

A time interval used to “check” the value of the analog signal(sampling)

Bit depth

The number of bits used to represent each sample rate.

• This comes from: the value from the sample rate is limited to a finite precision to be stored on a computer (quantization).

Quantization Noise/Quantization Error

When a bit that falls between two levels has to be rounded to the closest approximation

Sample rate & Bit depth for Audio for video

48kHz & 24bit

Sample rate & Bit depth for CDs, streaming, consumer audio

44.1kHz & 16bit

Sample rate & Bit depth Sizes

1 minute of mono:

• 16-bit/44.1 kHz = 5 mB

• 24-bit/44.1 kHz = 8 mB

• 33-bit/44.1 kHz = 10 mB

Stereo will be twice the size

Condenser mic

the sound pressure level varies the head capacitance of the mic by deflecting 1 or 2 plates of the capacitor

• most common for vocals (recording studios)

• better sensitivity

• can measure very high sound pressure levels

• phantom powered by 48 Vdc and 2 mA

• Cons: delicate & expensive

Dynamic mic

Has a small diaphragm and voice coil, moving in a permeant magnetic field

• poorer noise performance compared with Condenser mics

• the musician, performer, journalist can perform with it during live shows

• can measure very high sound pressure levels

• cheaper

Ribbon mic

Somewhat fragile mics, their high frequencies give them a slightly dull tonality to modern ears

• always bidirectional

• can measure very high sound pressure levels

• never for live situations

Polar Pattern

Microphones are classified by their pickup pattern or how they discriminate between the various directions the sound source comes from

Omnidirectional

pickup is equal in all directions

Bidirectional

pickup is equal from the 2 opposite directions (180°) apart and 0 from the 2 directions that are 90° from the first

Unidirectional (cardioid)

pickup is from 1 direction only, the pickup appearing

Microphone Sensitivity

measures the amount of output for a given input

• a.k.a: it tells you how loud a mic is

• the more sensitive a mic is, the louder the signal will be for a given input of sound

• typically measured: 1 kHz sine wave at a 94 dB sound pressure lvl

Mic Input

sound pressure level at the diaphragm

• measured in dB SPL or 1 pascal(Pa) pressure

Mic output

voltage across its output connection

• measured in mV or dBV

Lavalier Mics

Used for television, theater, and public speaking

• usually a condenser mic and omni-directional

  • this pickup pattern is best suited for the scenario of being fixed on an actor’s body

• effectively involves: placing them on the right spot, hiding them, and keeping them from rustling

• they are connected to a wireless transmitter, that send the signal to a receiver, connected to the recording device