AV Signal Fundamentals: Audio, Video, Analog vs Digital, Balanced vs Unbalanced
Learning objectives
- Explain what an AV signal is and the difference between audio and video signals.
- Compare analog and digital signal representations.
- Distinguish balanced and unbalanced audio connections and when each is appropriate.
- Relate signal properties to the cables and connectors that carry them.
Vocabulary
- Signal
- A changing voltage or data pattern that carries information.
- Analog
- A continuous waveform whose value varies smoothly with the source.
- Digital
- Discrete samples (numbers) that represent a waveform or image.
- Balanced audio
- A three-conductor audio link using a hot, cold, and ground that rejects noise.
- Unbalanced audio
- A two-conductor link (signal + ground) more susceptible to noise over distance.
- Impedance
- The opposition a circuit presents to alternating current; must be matched between devices.
Lesson content
An AV signal is information in motion. In audio it is a waveform representing sound pressure; in video it is a stream of pixel and color data representing an image, often many times per second.
Audio signals
A microphone produces a tiny analog voltage (millivolts) proportional to sound. A line-level signal is stronger (around 1 volt). A speaker output is higher still and driven by an amplifier. Matching these levels correctly is the heart of gain structure, which you will meet again in Week 4.
Video signals
Modern video is almost always digital. A source captures pixels as red/green/blue values at a resolution (e.g. 1920×1080) and a frame rate (e.g. 60 Hz). The signal carries resolution, color depth, timing, and optional audio together over interfaces like HDMI.
Analog vs digital
- Analog = continuous. Value can be anything within range; easy to corrupt with noise but intuitive to mix.
- Digital = sampled numbers. Resistant to noise up to a threshold, then fails hard. Can be copied losslessly.
- Converters (ADC and DAC) move between the two worlds; every digital audio chain starts and ends analog.
Balanced vs unbalanced audio
Balanced audio sends the same signal on two conductors with opposite polarity, then subtracts them at the receiver. Noise picked up equally on both conductors cancels out — this is common-mode rejection.
- Unbalanced (TS, RCA) — tip = signal, sleeve = ground. Fine for short runs (under ~3–5 m / 10–15 ft).
- Balanced (XLR, TRS) — hot, cold, ground. Rejects noise and supports long runs (tens of meters).
- Professional commercial audio uses balanced connections for mic and line runs inside walls and ceilings.
Do not split a balanced microphone signal with a passive Y-cable to two inputs and expect clean results. Use a proper splitter or route it inside the DSP. Unbalanced consumer outputs (RCA) should not be run long distances alongside data lines.
Worked example
A ceiling microphone on a 15 m / 50 ft run to a DSP below the desk: balanced XLR the whole way. A laptop's headphone jack feeding a small room's aux input 1 m away: unbalanced is acceptable, but a DI box gives you isolation and a balanced feed if the run must go farther.
Implementation checklist
- ✓Use balanced connections for mic and long line runs.
- ✓Match levels (mic → preamp → line) — do not plug a mic straight into a line input.
- ✓Keep unbalanced runs short and away from power and data cables.
- ✓Confirm impedance matches the destination (e.g. 600Ω line, 75Ω video).
Downloadable study guide
01. Audio levels rise mic (mV) → line (≈1V) → speaker (V); amps drive speakers, not DSPs. 02. Balanced audio = hot + cold + ground; common-mode noise rejection; long runs. 03. Unbalanced = signal + ground; short runs only. 04. Digital resists noise to a threshold then fails; analog degrades gradually. 05. Video carries resolution, color depth, timing, and often audio in one interface.