Fundamentals and Instruments
John Linsley HoodCHAPTER 30Audio equipment is, by defi nition, ultimately intended to provide sounds that will be
heard by a listener. Despite rather more than a century of experience in the electrical
transmission and reception of audible signals, the relationships between the electrical
waveforms into which sound patterns are transformed and the sound actually heard by the
listener are still not fully understood.
This situation is complicated by the observable fact that there is a considerable
variation from person to person in sensitivity to, and preferences in respect of, sound
characteristics, particularly where these relate to modifi cations or distortions of the sound.
Also, since the need to describe or indeed the possibility of producing such modifi ed
or distorted sounds is a relatively new situation, we have not yet evolved a suitable and
agreed vocabulary by which we can defi ne our sensations.
There is, however, some agreement, in general, about the types of defect in electrical
signals that, in the interests of good sound quality, the design engineer should seek
to avoid or minimize. Of these, the major ones are those associated with waveform
distortion, under either steady-state or transient conditions; the intrusion of unwanted
signals; relative time delays in certain parts of the received signal in relation to others;
or changes in the pitch of the signal, known as “ wow ” or “ fl utter, ” depending on its
frequency. However, the last kind of defect is only likely to occur in electromechanical
equipment, such as turntables or tape drive mechanisms, used in the recording or replay
of signals.
It is sometimes claimed that, at least so far as the design of purely electronic equipment is
concerned, the performance can be calculated suffi ciently precisely that it is unnecessary