Intro To Audio Part 2 electric boogaloo

Equalization (EQ)

Frequency Dependent Control of Amplitude

Low Pass/High Cut filter

Cuts off high frequencies at a certain point leaving the lower frequencies audible

Low Cut/High pass filter

Cuts off low frequencies at a certain point, leaving higher frequencies audible

Shelving filter/High boost and cut

Filter to boost or cut a wide range of frequencies equally

Graphic EQ

A control surface that gives a graphical representation of how you are affecting the balance of frequencies

1/3 octave graphic EQ

each band covers 1/3 of an octave (major 3rd)

Fully parametric EQ

each band (typically 3-5) has fully variable control of three parameters

The three bands most commonly seen on parametric EQ

Center Frequency, Boost/Cut, Bandwidth or Q

What is Q

Center Frequency/Bandwidth

Dynamics Processors

Processors that manipulate dynamic range

Compression

a variable gain amplifier; once the input exceeds a threshold, output gain decreases as input increases

Threshold

The input level at which compression begins

Ratio

Number of dB in above the threshold that yields one dB out

Attack Time

the amount of time a compressor waits to start working once signal has crossed the threshold

Release Time

How long after the input signal drops below the threshold until the compressor returns to unity gain

Function of a Limiter

has a ratio of 10/1 or higher, essentially limiting, or putting a ceiling on the output

Hard Knee

Transitions to compression abruptly

Soft Knee

Transitions to compression over a range

Sidechain or Key input

Triggers compression of one signal with another signal (often a bass with a kick drum)

Expander or Noise Gate

Signals above the threshold remain at unity gain; signals below the threshold are made quieter

What are Delay and Reverb

Time Based Processors made up of actual, or simulated, reflections of sound waves

Delay

Made up of discreet reflections; heard as individual events

Reverb

Made up of a multiplicity of reflections, too close together in time to be individually discernable

Analog tape delay

While in record mode, send a signal to the record head; the time it takes the tape to travel to the playback head is the delay time

Feedback

feeding the output of a device back into its input in order to get repeating delays

Digital Delay

digital recorders that hold onto a signal and then release it after a time

VCO

Voltage controlled oscillator

LFO

Low frequency oscillator

what does VCO and LFO do

Produce a varying waveform in the analog digital domain that is used to modulate the parameters of delays and other devices

Phasing, Flanging, and Chorus

all produced using a VCO/LFO to modulate delay times

Early Reflections (Reverb)

give a sense of how big the space is and where you are in it

Onset of Reverb

begins when reflections build up in the space to form a wash of sound

Reverb Time

determined by how reflective the space is

RT60

how long it takes the reverb to decay 60dB

Chamber Reverb

a dedicated space (chamber) with a speaker in it and one or more microphones; we send a signal to the speaker and capture the reverb with the mics

Plate Reverb

Utilizes a metal plate suspended in a box like enclosure, a driver excites the plate and contact microphones pick up the vibrations dissipated in the plate

Spring Reverb

energy is dissipated in one or more springs and picked up the same way as plate reverb

Digital Reverb

uses algorithms to mimic the sounds of the other three methods of reverb, and of all kinds of spaces.

doubling delays

delays that are not heard as individually discernible events, but are not reverb.

The Haas effect

Short delays are perceived as coming from different places but are not heard as echoes

Direct/Reverb Ratio

the balance between the direct sound a source and the reverberant sound in a space.

Digital Audio

Computer based encoding and decoding of a waveform

Two big advantages of digital over analog

1. You can use computers to manipulate audio

2. There is no noise from storage media on playback

Binary Numbers

Utilize 1’s and 0’s to allow computers to make calculations super fast

How many values does a 16 bit word have?

0 - 65,536

What is a Sample

an instantaneous snapshot of amplitude

Sample Rate

how many samples are taken per second

Sample and Hold

this takes a sample and holds that value until the next sample is taken

Nyquist Rule

As long as the sample rate is at least 2x higher than the highest frequency present in your signal, you retain all the information.

Nyquist Frequency

the high frequency limit of a sampler

Aliasing

a frequency at the output that was never at the input; happens when you violate the Nyquist rule

Anti-Aliasing filter

a low pass filter that cuts off any frequency higher than half the sample rate

Quantization

the approximation of amplitude; rounding up or down to the nearest available quantization level

Analog to digital converter

outputs the 16 bit word that corresponds to the quantized amplitude

Multiplexor

takes the 16 bit parallel of the A/D converter and puts it into serial, or sequential form

low level distortion

when a waveform doesn’t cross at least 2 quantization levels, it gets quantized to only one, and causes distortion

Dither

a low level noise that is added to all inputs to ensure that all signals cross at least two quantization levels

Error protection and interleaving

the scrambling of the data on the storage medium so that any damage affects small parts of many digital words instead of wiping out entire words

Disadvantage of digital compared to analog

digital audio has a counterintuitive distortion characteristic

2/1 rule

the distance between microphones should be at least twice the distance from the microphones to the sound source

Granulation noise

the sound artifacts that can occur during the process of granular synthesis

What is Bandwidth

The range of frequencies that a device can handle