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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

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What is audio signal flow l.jpg
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


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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: 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)


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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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Quarter-inch TS

Quarter-inch TRS

Signal

Ground

Signal +

Ground

Signal -

RCA

XLR

“Pin-out” of typical connectors

UNBALANCED

BALANCED



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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”- Webster’s 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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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 l.jpg
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 l.jpg
    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 l.jpg
    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 l.jpg
    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 ADC’s and DAC’s built into them. Some soundcards even have built-in preamps.

    (microphone)

    Preamp

    ADC

    SOUNDCARD

    Computer/Recorder

    DAC

    Power Amp

    (speaker)

    (headphones)


    Summary l.jpg
    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


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