ABSTRACT
Facilities that alter the shape of the frequency response are called tone controls when they are
incorporated in hi-fi systems, and equalization (or EQ) in mixing consoles.
Tone controls have suffered at the hands of fashion for some years now. It has been claimed
that tone controls cause an audible deterioration even when set to the flat position. This is
usually blamed on ‘phase-shift’. For a long time tone controls on a preamp damaged its
chances of street (or rather sitting room) credibility, for no good reason. A tone control set to
‘flat’ – assuming it really is flat – cannot possibly contribute any extra phase-shift unless you
have accidentally built in an all-pass filter, which would require truly surreal levels of
incompetence, and so the control really must be inaudible. My view is that hi-fi tone controls
are absolutely indispensable for correcting room acoustics, loudspeaker shortcomings, or the
tonal balance of the source material, and that a lot of people are suffering suboptimal sound as
a result of this fashion. It is commonplace for audio critics to suggest that frequency-response
inadequacies should be corrected by changing loudspeakers; this is an extraordinarily
expensive way of avoiding tone controls.
