Page 138 - The Master Handbook Of Acoustics

113
SPEECH, MUSIC, AND NOISE

5600

White 2700 820 270 Pink
noise 0.05 noise
in out
1.0 0.1
0.316

FIGURE 5-19
A simple filter for changing white noise to pink noise. It changes random noise of con-
stant energy per Hz to pink noise of constant energy per octave. Pink noise is useful in
acoustical measurements utilizing analyzers having passbands with bandwidth of a con-
stant percentage of the center frequency. General Radio Company 1

to the precious signal in passing through transducers, amplifiers,
and various forms of signal processing gear. Here is an incomplete
list: 8,9,10
Bandwidth limitation If the passband of an amplifier cuts lows or
highs, the signal output is different from the input. If the scratch filter
reduces record surface noise, the overall effect can be improved, but
basically the signal itself is the poorer for it.
Nonuniform response Peaks and valleys within the passband also
alter the signal waveshape.
Distortions in time If tape travels across the head at any other
than the recording speed, the frequency components are shifted up or
down in frequency. If there are slow or fast fluctuations in that speed,
wow and flutter are introduced and the signal is degraded.
Phase distortion Any phase shifts introduced upset the time rela-
tionship between signal components.
Dynamic distortion A compressor or expander changing the
original dynamic range of a signal is a form of distortion.
Crossover distortion In class-B amplifiers, in which the output
devices conduct for only half of the cycle, any discontinuities near
zero output result in what is called crossover distortion.
Nonlinear distortion If an amplifier is truly linear, there is a
one-to-one relationship between input and output. Feedback helps
to control nonlinear tendencies. The human ear is not linear. When