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NOISE - PowerPoint PPT Presentation


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NOISE Images provided by Tristan… Noise Noise refers to the residual low level sound that is heard in quiet periods. Commonly called HISS and HUM Can be in AUDIO RECORDINGS, or LIVE BROADCAST Types of Noise One kind is the acoustic noise from loudspeakers

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noise3
Noise
  • Noise refers to the residual low level sound that is heard in quiet periods.
  • Commonly called HISS and HUM
  • Can be in AUDIO RECORDINGS, or LIVE BROADCAST
types of noise
Types of Noise
  • One kind is the acoustic noise from loudspeakers
  • The other is the unwanted residual electronic noise heard as 'hiss’.
a weighting
A-Weighting
  • The process of measuring noise levels
  • Shows how noisy equipment is
slide6

Noise is often generated on purpose and used as a test signal.

  • 'white noise’ has a uniform spectral power density at all frequencies
  • 'pink noise’ has a spectral power density that falls at 3dB/octave with rising frequency.
pink noise
PINK NOISE
  • PINK NOISE is often more useful in audio testing because it contains constant energy per octave
  • It contains energy that is distributed more evenly rather than linearly
pink noise continued
PINK NOISE Continued…
  • As mentioned, Pink Noise drops 3dB per octave
  • It is a RATIO: Frequency vs. decibels
white noise
White Noise
  • White noise is a random signal (or process) with a flat spectral power density.
  • The signal contains equal power within a fixed bandwidth at any center frequency.
  • White noise draws its name from white light
  • It’s like FUZZ on a TV
signal to noise ratio
Signal to Noise Ratio
  • Similar to Dynamic Range
  • The signal to noise ratio is the difference between the noise floor and the reference level.
  • The reference level is determined by the person making the measurements.
common s n levels
Common S/N levels
  • Microphones: 140 dB
  • FM Radio: 50-60 dB
  • 16-bit CD audio: 96 dB
  • 24-bit audio: 144 dB
  • (Digital audio is approx. 6dB per bit)
misleaing s n ratio
Misleaing S/N Ratio
  • S/N measurements can be misleading because other factors come into play
  • Wattage (power output) involved or chosen signal level can affect the S/N ratio