Analog vs Digital Audio: Levels and Conversions

• Analog audio uses continuous electrical flow for audio signals.
• Digital audio uses discrete/discontinuous values (1s & 0s) for audio signals.
• Analog to digital converters are the inputs of an audio interface.
• Digital to analog converters are the outputs of an audio interface.
• Microphones, speakers, and headphones are transducers.
• Transducers change one form of energy into another.
• Microphones change mechanical energy into electrical voltage.
• Speakers and headphones change electrical voltage into mechanical energy.
• Magnetic tape recorders convert electrical audio signals into analogous patterns of magnetic fluctuation.

Analog Audio Level Standards

• Microphone level is the lowest level, measured in single millivolts.
• Instrument level is next, measured in tens of millivolts.
• Line level follows, measured in single volts.
• Speaker level is the highest, measured in tens of volts.

Analog Audio Level Transformations

• Preamplification is needed to change from microphone or instrument level to line level.
• Amplification is needed to change from line level to speaker level.
• Active speakers accept line level and change it to speaker level with an on-board amplifier.
• Passive speakers accept speaker level from a power amplifier.
• Passive speakers do not have an on-board amplifier.

Basic Electricity

• Valence electrons in the outermost shell are unstable and can move between atoms.

• Free electrons are valence electrons that have broken free from the atom.

• Electrical flow involves the movement of valence electrons.

• Current flows when free electrons connect to neutral or positively charged atoms.

• Atoms with few valence electrons are good conductors (copper, aluminum).

• Atoms with many valence electrons are good insulators (rubber, plastic, glass).

• Current measures the rate of flow of free electrons, measured in amperes/amps.

• Voltage is the electromotive force pushing free electrons, measured in volts.

• Resistance impedes the flow of current, measured in Ohms Ω.

Electromagnetic Induction and AC

• Electromagnetic induction requires a moving magnetic field and a fixed conductor, or vice versa.
• Moving coil microphones use a magnet, coil of wire, and a diaphragm.
• Ribbon microphones use a magnet, corrugated aluminum ribbon, and a step-up transformer.
• Passive guitar pickups use a magnet, coil of wire, and a steel string.
• Direct Current (DC) moves in one direction.
• Alternating Current (AC) alternates between positive and negative.

United States AC Standards

• AC frequency in the US is 60 Hertz.
• Standard household voltage in the US is 120 volts.
• Standard household amperage in the US is 10, 15, or 20 amps.

Impedance

• Resistance in an AC circuit is constant across all frequencies.
• Impedance (Z) is a frequency-dependent type of resistance.
• Impedance is measured in Ohms Ω.
• Bridging Impedance systems need an input/load impedance at least 10x the output/source impedance.
• Matching Impedance systems need an input/load impedance equal to the output/source impedance.
• Microphone preamps and devices like the Cloudlifter Z can provide impedance loads.
• These loads apply to moving coil, ribbon microphones, and instrument level inputs.

High Z and Low Z

• High Z interconnections can filter high frequencies and are susceptible to noise.
• Instrument cables should be short (under 15 ft) and have low capacitance.
• Instrument level in electric guitars/basses is the only High Z system in pro audio.
• All microphone/line level equipment used in a professional audio studio are always Low Z.

Unbalanced Connections

• Unbalanced systems reject noise with the braided shield connected to ground.
• They have two connection points: inner conductor and shield/ground.
• Unbalanced cabling should be short for both Hi or Low Z.
• AC current conductors (power cables) create fluxing magnetic fields at right angles to the conductor.
• The magnitude and rate of the magnetic field is analogous to the AC current.

Balanced Connections

• Balanced Systems use twisted pair cables.
• They have three connection points: Hot/+, Cold/-, and Shield/Ground.
• The same signal is on both conductors of the twisted pair.
• The Cold/- connection is polarity reversed from the Hot/+ connection.
• Conductors polarity reverses, so the noise accumulating on these conductors is the same polarity.
• Balanced connections only accept different signals.
• The Cold/- signal’s polarity is reversed to match the Hot/+ signal, and volumes are summed.
• Common signals (noise on the pair) are rejected at the input.
• Star Quad cable uses four conductors and the shield/ground.
• Star Quad cables use two conductors for the Hot/+ and two for the Cold/-.
• Star Quad cables have superior EMI rejection compared to twisted pair.

Audio Interfacing Examples

• Electric Guitars and Basses are Unbalanced, Hi-Z, and instrument level.

• Professional mics are Balanced, Low-Z, microphone level.

• Microphone preamps accept Balanced, Low-Z, Microphone level.

• Many preamps accept Unbalanced, Hi-Z, Instrument Level.

• Microphone preamps always produce Balanced, Low-Z, Line Level at their outputs.

• The Lynx Aurora accepts Balanced, Low-Z, Line Level at its analog inputs.

• The Lynx Aurora produces Balanced, Low-Z, Line level at its analog outputs.

• DIs accept Unbalanced, Hi-Z, Instrument Level at their inputs.

• DIs produce Balanced, Low-Z, Microphone Level at their outputs.

• Passive DIs use a step-down transformer with more primary winding turns than secondary.

• Passive DIs use a 10:1 winding ratio.

• Transformers are Bi-Directional and act as step-up transformers (when the secondary winding output is the input).

• Active DIs need power and a tube or FET and are unidirectional.

• A Reamp Box accepts Balanced, Low-Z, Line Level at its inputs.

• A Reamp Box produces Unbalanced, Hi-Z, Instrument Level at its output.

• Two DIs can create a remote amp setup, where the sending DI can be passive or active.

• The sending DI balances the guitar signal and steps down the level and Z.

• The "receiving” DI must be passive and the “sending” signal connects to its output (secondary winding).

• This allows the signal to be stepped up in level, the signal made unbalanced, and Z adjusted.

Explanation of analog and digital audio signals, including analog-to-digital and digital-to-analog converters in audio interfaces. Transducers like microphones and speakers are discussed. Also covers analog audio level standards: microphone, instrument, line, and speaker levels.