Transcript Week 3 - Making the Right Connections

Making all the right
connections
Signal Flow 101
What is Audio Signal Flow?
 Audio: “Of or relating to sound or sound
reproduction” – Webster’s II New Riverside Dictionary
 Audio Signal: “a representation of sound waves in a
different form. Typically this is an electrical
voltage…An audio signal can be manipulated, stored,
transmitted and reproduced in ways that a sound
wave cannot.” - http://en.wikipedia.org/wiki/Audio_signal
 Audio Signal Flow: “the term used to describe the
path an audio signal will take from source
(microphone) to the speaker or recording device.” http://en.wikipedia.org/wiki/Audio_signal
Rules of Signal Flow
 Rule #1: Things always work better when they are
plugged in…
 Rule #2: Outputs are connected to Inputs (and vice
versa)
 Basic Plumbing - the signal only flows in one direction
 Follow the electrons (hint: they’re inside the cable)
 Audio signals require at least two wires: one for
signal and one for ground
 (Don’t confuse WIRE with CABLE – one CABLE can
contain several wires)
Common Audio Connectors
 Balanced (professional equipment)
 XLR
 1/4-inch TRS
 Unbalanced (consumer equipment)
 1/4-inch TS
 RCA
Balanced vs. Unbalanced
 An audio cable is an antenna - it picks up
noise along its length
 The signal cannot be separated from the
noise on an unbalanced signal
 A balanced signal can eliminate this noise
through “destructive interference”
 Unbalanced cables require two conductors,
 Balanced cables require three
“Pin-out” of typical connectors
UNBALANCED
Quarter-inch TS
Signal
Ground
RCA
BALANCED
Quarter-inch TRS
Signal +
Ground
Signal -
XLR
How noise affects a signal
A bit about “polarity” and “phase”
 Sound waves alternate between high pressure
and low pressure
 Electrical audio signals alternate between
positive (+) and negative (-)
 Polarity indicates a positive or negative value
 Musical Sounds have a repetitive wave pattern a cycle that repeats
 Phase tells us where we are in a cycle
 Phase is measured in degrees or radians
 One complete cycle = 3600 of phase
How “balanced” works
+
Same signal
polarity inverted
Same
noise
gets into
both
signals
=
Polarity inverted again
- signal “in-phase”
noise “out-of-phase”
Signal twice
as strong;
noise
cancels out
Male vs. Female
 use your imagination…
 With XLR, male tends to be an output
and female tends to be an input
 An XLR cable generally has two genders
 1/4-inch and RCA cables are generally
male at both ends
What level is it?
Every input expects ONE TYPE of level.
Mismatching can result either in distortion or
no usable signal
 Mic level - smallest (-60 dB)
 XLR connector
 Consumer level (-10 dB)
 Home stereo equipment
 VCR/DVD/TV
 Uses RCA connectors
 Line Level - highest (+4 dB)
 Professional equipment - mixers, preamplifiers,
keyboards, recording equipment, etc.
 1/4-inch or XLR connector
Gain Staging
 Signal must be the right level for the next
piece of equipment in the chain
 Too small = signal lost in noise
 Too big = distortion (“clipping”)
 Gain: “an increase”
 Any point in the signal chain where the
amount of signal can be adjusted (boosted) is
called a “Gain Stage”
 Mic-level signals must be raised to linelevel for recording - “Microphone Preamp”
- Webster’s II New Riverside Dictionary
Simple Signal Flow
Preamp
(microphone)
Power Amp
(speaker)
Mono vs. Stereo
 Mono literally means “one”
 Mono is one distinct channel of audio
information
 Stereo comes from the Greek “stereos”
meaning “solid” or something that has length,
width, and height
 Stereo is an aural illusion which requires two
or more distinct channels of information
Channel vs. Track
 Channel: “a means of passing,
transmitting, or communicating.”
 Webster’s II New Riverside Dictionary
 Track: a place to store audio
information
Multitrack Recording
 When you are recording to more than one
track, this is called multitrack recording
 In the recording studio, a number of
microphones or sources can be recorded
simultaneously
 The signal from each mic and/or source can
be recorded to a different track so that it can
be processed separately and mixed later
 You can also record one mic (or source)
several times to make it sound like it all
happened at the same time (overdub)
Analog Recording
 Comes from the word “analogous” meaning
“similar to” or “the same as”
 The voltage changes coming from the
microphone will have absolute correlation
with the changes in air pressure caused by
the sound wave that moved the diaphragm
 The fluctuations in the magnetic field
recorded onto analog tape will have absolute
correlation with the voltage changes from the
microphone
 Analog records continuously - there is no gap
in the recorded information
Digital Recording
 An Analog signal has a constantly changing value;
 A Digital signal is a series of pulses of only two
values (on/off)
 Analog to Digital Converter (ADC) - takes regular
measurements of the analog signal (samples) and
converts each measurement to a numeric (digital)
value
 The value of each sample is indicated by a pattern
of on/off pulses
 The series of samples is then stored (recorded)
 Digital to Analog Converter (DAC) - converts the
digital signal back to a continuous analog signal
 More on this later…
(microphone)
TYPICAL SIGNAL FLOW IN A DIGITAL AUDIO
CHAIN
A computer needs a soundcard (aka Audio Interface)
to receive or send audio signals. Often, the computer
acts as a Digital Recorder. Usually, the soundcard
will convert the signal from ANALOG to DIGITAL for
the computer. Then, it converts the DIGITAL signal
from the computer back to ANALOG to be played
back for humans
SOUNDCARD
Preamp
ADC
A computer soundcard can be internal or external.
Many external soundcards use Firewire or USB. All
computer soundcards have ADC’s and DAC’s built
into them. Some soundcards even have built-in
preamps.
Computer/Recorder
DAC
Power Amp
(headphones)
(speaker)
Summary
 Signal only flows in one direction
 Outputs are connected to inputs
 There are three basic signal levels: mic (-60dB),
consumer (-10dB), and line (+4dB)
 Unbalanced signals: 2 conductors - signal and
ground; CANNOT eliminate noise picked up on the
cable
 Balanced signals: 3 conductors: signal + , signal - ,
and ground; CAN eliminate noise picked up on the
cable
 Gain Staging: optimizing the signal level for the
next device in the signal chain