Making all the right connections

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Making all the right connections

• Signal Flow 101

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What is Audio Signal Flow?

• Audio Of or relating to sound or sound
  reproduction Websters II New Riverside
  Dictionary
• Audio Signal a representation of sound waves in
  a different form. Typically this is an electrical
  voltageAn audio signal can be manipulated,
  stored, transmitted and reproduced in ways that a
  sound wave cannot. - http//en.wikipedia.org/wik
  i/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

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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 theyre inside the
  cable)
• Audio signals require at least two wires one for
  signal and one for ground
• (Dont confuse WIRE with CABLE one CABLE can
  contain several wires)

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Common Audio Connectors

• Balanced (professional equipment)
• XLR
• 1/4-inch TRS
• Unbalanced (consumer equipment)
• 1/4-inch TS
• RCA

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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

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Pin-out of typical connectors
UNBALANCED
BALANCED
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How noise affects a signal
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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

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How balanced works


Signal twice as strong noise cancels out
Same noise gets into both signals
Same signal polarity inverted
Polarity inverted again - signal in-phase noise
out-of-phase
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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

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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

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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 - Websters II New Riverside
  Dictionary
• 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 line-level
  for recording - Microphone Preamp

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Simple Signal Flow
Preamp
Power Amp
(speaker)
(microphone)
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Channel vs. Track

• Channel a means of passing, transmitting, or
  communicating.
• Websters II New Riverside Dictionary
• Track a place to store audio information

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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

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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)

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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

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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

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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 A computer
soundcard can be internal or external. Many
external soundcards use Firewire or USB. All
computer soundcards have ADCs and DACs built
into them. Some soundcards even have built-in
preamps.
(microphone)
Preamp
ADC
SOUNDCARD
Computer/Recorder
DAC
Power Amp
(speaker)
(headphones)
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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