
Chapter
4 Audio-frequency signals and
reproduction
Audio frequencies are those within the range of
hearing - which is a definition vague enough to
mean different things to different people. To the
line communication engineer, everything has to fit
within a 4 kHz wide telephony channel, whilst to
the radio telephone engineer, audio frequencies
are those between 300 Hz and 3 kHz. To the hi-fi
enthusiast the definition means 20 Hz to 20 kHz,
no less, even though only the young can hear
sound waves of 15 kHz and above.
In this chapter we look at the amplification of
audio-frequency electrical signals and their trans-
formation into sound waves