Audio Systems 2 - Study Guide


Fundamentals of Power and Electricity

  • Be prepared to solve for electrical variables using Ohm's Law.

    • Ohm's Law: V=IRV = IR, where V is voltage, I is current, and R is resistance.

The Role of Ground in Electricity

  • “Ground” serves as a safety measure and a return path for electrical current.

  • Protects people and equipment from electrical shock and damage.

  • Ground lifts in DI boxes are necessary to eliminate ground loops, which can cause buzz in audio signals, and reduce/cancel noise.

The Decibel (dB)

  • Definition: A logarithmic unit used to express the ratio of two values of a physical quantity, often power or intensity.

  • 10 log (W1/W0) for power ratios

  • 20 log (W1/W0) for voltage or sound pressure ratios

10 log vs 20 log

  • Use 10log⁡10 \log when dealing with power ratios.

  • Use 20log⁡20 \log when dealing with voltage, current, sound pressure, or amplitude ratios.

Pro Audio Levels vs Consumer Audio Levels

  • Pro Audio Level: line level @ -10dBV (0.316vrms)

    • 0 dBu = 0.775Vrms

  • Consumer Audio Level: line level @ +4dBu (1.23vrms)

    • 0 dBV = 1Vrms

  • Consumer to Pro gear is okay, Pro to Consumer gear can cause overload.

Basic Electronic Components

  • Roles of various electronic components:

    • Transformers: Devices that transfer electrical energy from one circuit to another through electromagnetic induction; used for voltage step-up/step-down and isolation.

    • Capacitors: Components that store electrical energy in an electric field; used for filtering, smoothing, and coupling/decoupling signals.

      • 2 charged plates with a gap or dielectric material in
        the middle

      • Similar to a battery – can store and then discharge
        electricity

      • When used in an AC system, it resists LF information
        and passes HF

    • Resistors: Components that resist the flow of electric current; used to control current, divide voltage, and provide bias.

    • Inductors: Components that store energy in a magnetic field; used in filters, oscillators, and power supplies.

      • A coil of wire around a piece of metal

      • Electricity induces a magnetic flux which in turn
        fights against the electric current of the coil

      • LF is allowed to pass, while HF current is filtered

    • Transistors: Semiconductor devices used to amplify or switch electronic signals and electrical power.

Impedance

  • Definition: The measure of opposition to alternating current (AC) in an electrical circuit; includes resistance and reactance.

  • Symbolized by Z, measured in ohms (Ω).

    • Z=R+jXZ = R + jX, where R is resistance and X is reactance.

  • Capacitors, inductors, and transducers can be used to create reactance.

    • Mic output: (low-z) 50-
      200Ω, as high as 600Ω

    • Line output: (low-z) around
      100Ω

    • Microphone Preamp: 1-
      2.5kΩ (relatively low, but still
      satisfies the 1:10 rule)

    • Line input: 10kΩ +

Impedance Matching vs Impedance Bridging

  • Impedance Matching: Making the output impedance of a source equal to the input impedance of the load to maximize power transfer (typically used in RF and high-power applications).

    • • Vout=Vs*(ZL/(ZL+Zs))
      • Vout = Our new voltage
      • Vs = voltage source
      • ZL = input impedance (where we’re going)
      • Zs = Output impedance (Signal source)

  • Impedance Bridging: Making the input impedance of the load much higher than the output impedance of the source to maximize voltage transfer and minimize loading effects (typically used in audio signal transmission).

    • Vout=Vs*(ZL/(ZL+Zs))

    • High input impedance, low output impedance

Dynamic and Condenser Microphones

  • Dynamic:

    • Coil attached to a diaphragm

    • Coil sits over a magnet

    • Diaphragm moves the coil – magnetic field
      causes electricity to alternate back and forth

  • Condenser:

    • A condenser uses two charged plates

      • One in back is rigid

      • One in front is movable and acts as our
        diaphragm

      • The movement changes the capacitance
        up and down, which translates to an AC
        signal

    • Condensers need to be powered

      • Can’t have two charged plates without some charge

Phantom Power

  • Phantom power (48V) provides the DC voltage needed for condenser mics to operate and polarize the diaphragm.

  • Explain how it works: DC voltage supplied through the same cable as the audio signal (XLR).

    • Powered through output signal

Balanced vs Unbalanced Audio

  • Balanced Audio: Uses three conductors (two signal wires and a ground) to reduce noise through common-mode rejection.

  • Unbalanced Audio: Uses two conductors (one signal wire and a ground), more susceptible to noise.

Cables

  • Compare and contrast different audio cables:

    • RCA cable: Unbalanced, typically used for consumer audio.

    • TRS cable: Can be balanced (Tip-Ring-Sleeve) or unbalanced (Tip-Sleeve), used for various audio connections.

    • XLR cable: balanced cable that is high quality and has three pins, ground/shield, red/hot, black/cold.

      • Signal is split, signal on pin 3 flips polarity, eliminates noise


Computer Components

  • Define the roles of basic components inside a standard computer:

    • Power Supply: AC to DC, contains lots of connectors so individual elements can be powered.

    • Motherboard: Large circuit that acts as a physical, electrical foundation for all connected components.

      • CPU: Central Processing Unit, performs calculations and executes instructions.

      • RAM: Random Access Memory, temporary storage for data and instructions.

      • GPU: Generates graphical elements

      • ROM, BIOS: Why you can hard reset your computer and it boots up again.

      • CMOS: Why you can unplug your computer and the computer still knows what time it is, important for connecting to the internet.

    • Expansion Cards: Ability to add extra visual and audio cards for more storage.

    • Storage: Where all info is stored, can be a hard drive.

    • Cooling: Fans designed to keep computer cool.

    • I/O: Ways to plug into and out of a computer.

Software

  • Audio MIDI Setup (macOS): Control all I/O for the computer.

  • Disk Utility (macOS): Hard drive maintenance and reformatting.

  • Activity Monitor (macOS): Understand what’s running on your computer, close things that aren’t responding.

Kernel Panic

  • Kernel: Runs the operating system, loads first, controls how different parts run.

  • Definition: A fatal system error on macOS, kernel stops working. Happens due to incompatible RAM, hard disk corruption, etc.

  • Troubleshooting: Restart the computer.

Safe Mode on Mac

  • Definition: All “extra” programs do not run during startup, OS runs with minimal features, good way to troubleshoot problems.

Recovery Mode on Mac

  • Definition: A special boot mode that allows users to reinstall macOS, repair disks, and restore from backups.

MIDI

  • Define MIDI: Musical Instrument Digital Interface, a protocol for communicating musical information between electronic instruments and computers.

  • Compare MIDI to digital audio: MIDI transmits instructions, while digital audio transmits sound recordings.

    • Digital audio is used for recording and playback of music, sound effects, and voiceovers. MIDI is used for creating and controlling electronic music.

    • For MIDI, one instrument can create infinite sounds. For digital audio, one instrument creates one sound.

Sampler vs Synth

  • Sampler: An electronic instrument that records and plays back audio samples.

  • Synth: Taking waveforms and creating new sounds, often with oscillators, modifiers, and filters.

    • Synthesizer generates its own sound by manipulating waveforms, sampler plays back pre-recorded audio samples.

ADSR (Synthesizers)

  • ADSR: Attack, Decay, Sustain, Release - parameters that control the envelope of a sound.

Video

  • Understand the relationship between shutter speed, aperture, and ISO:

    • Shutter Speed: The duration for which the camera's shutter is open, affecting motion blur and exposure.

      • More shutter speed means less light hits film, but less blurry.

    • Aperture: The size of the lens opening, affecting depth of field and exposure.

      • Wider aperture means more light is let in, bigger depth of field.

    • ISO: The sensitivity of the camera's sensor to light, affecting noise and exposure.

      • Lower numbers need more light but the image is clearer, less noise.

Interlaced vs Progressive Image Rendering

  • Interlaced: Displays alternating lines of an image (fields) to create a full frame.

  • Progressive: Displays all lines of an image (frame) at once.

Color Bit

  • Definition: The number of bits used to represent the color of a single pixel.

    • 8 bit – 16,777,216 colors

    • 10 bit – 1 billion colors

    • 12 bit – 68 billion colors

Color Space

  • Definition: The range of colors that can be displayed or reproduced.

Gen Lock

  • Definition: A technique of synchronizing the scanning process of multiple video sources.

Time Code

  • Definition: A system for labeling individual frames in a video or audio production.

  • Drop vs Non-Drop: Different methods of counting frames to maintain accurate timekeeping.

Ways to Capture Audio on Set

  • Boom microphones, lavalier microphones, etc.

AAF vs OMF

  • AAF (Advanced Authoring Format) and OMF (Open Media Framework) are file formats for exchanging media between different editing systems.

    • AAF retains more data, supports larger file sizes, is considered more reliable and easy to use, becoming the common standard.

Troubleshooting Strategies

  • Describe some strategies for successful troubleshooting, such as:

    • Walk into the situation with knowledge already of how each part
      works

    • Stay calm in the moment

    • Identify the problem – describe it in detail

    • Identify the last time you “saw” audio

    • Middle-out technique: starting in the middle of the system rather than the top or bottom to effectively narrow down the source of the problem.