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 • The other is the unwanted residual electronic noise heard as 'hiss’.
A-Weighting • The process of measuring noise levels • Shows how noisy equipment is
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 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… • As mentioned, Pink Noise drops 3dB per octave • It is a RATIO: Frequency vs. decibels
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 • 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 • 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 • 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