Hum, Noise and Distortion

TVCA Audio Class #1	2. Conducting the Sound
Bringing it Back Alive
Hum, Noise Distortion, and Crosstalk

Many things can happen to the best audio signal.
Hum, Noise, Distortion and Crosstalk are the top four.

HUM
- What it is
  - A specific kind of noise: 60 Hz tone (and harmonics)
- What causes it
  - Coupling from power lines (especially lighting with dimmers)
  - Loose or damaged cables or connectors (broken grounds/shields)
  - Sometimes caused by inductive coupling from power transformers
- How to get rid of it
  - Check full length of signal path for cable or connector problems
  - Move audio cables away from power (or video) cables

NOISE
- What it is
  - Unwanted artifacts riding along with your desired signal
- What causes it
  - Improper level matching: too much gain at one stage
  - Sometimes caused by broken equipment, low batteries, bad tuning on wireless, etc.
- How to get rid of it
  - Check signal path for proper signal levels in and out.

DISTORTION
- What it is
  - Unwanted modification of your signal
- What causes it
  - Usually signal too "hot" at one point, overloading an input
  - May be caused by setting gain too high at one point in chain
  - Sometimes caused by dirty or corroded connectors or bad cables
- How to get rid of it
  - Check signal path for proper signal levels in and out.

CROSSTALK
- What it is
  - Some other audio signal leaking into yours
- What causes it
  - Coupling between two audio signals, high level (speaker) cable next to low level mic cable
  - Can also be caused by improper mixer settings
  - Sometimes caused by accidental reception of radio signals
- How to get rid of it
  - Check position of cables: not too close to others, or crossing at right angles
  - Check mixer settings, turn down (or off) any inputs you aren't using
  - Check cables and connectors (and mics) if picking up radio signals