Tony Andrews, famed designer of Turbosound and Funktion One, dishes
on audio system distortion. We “Men of Audio,” as my
friend Clifford Henricksen put it in one of his frequent moments
of levity, fight either the good fight for good sound or high fidelity.
But let’s just take a look at the words high fidelity, or
hi-fi. Taken literally hi-fi large quantities of faithfulness to
the original sound; in other words we’re talking truth, or
purity. Accordingly, the next concern is how shall you judge fidelity,
and how do you maximize it?
CRITERIA FOR FIDELITY
Even frequency response. The desirability of flat response
is self-evident, but in practice this is not as important as believed.
This is fortunate for loudspeaker manufacturers as very few products
are in fact flat.
The sound system is able to run comfortably, delivering
the required sound levels. Conservative operation is common
sense and good practice when operating any kind of machine. As far
as audio goes, it maintains headroom by giving peak signals room
to breathe.
Absence of clipping, harmonics, artifacts, and so on.
Signal integrity is where things go horribly wrong and are often
completely out of control. As it is the most important aspect of
fidelity, we find ourselves all too frequently involved in an uncomfortable
audio experience. One is able to ameliorate frequency response,
and a flat out sound system can always be turned down. As this is
very often psychologically difficult for some people, one can always
get in more amplifiers and speakers.
However, it is very rare, if not impossible, to regenerate a degraded
signal. The concept of fidelity is replaced by all manner of noxious
waveforms, which is a matter of great concern to me. Apart from
being entirely offensive, it is actually very damaging to human
hearing. In fact, distortion is more damaging to hearing than level.
This is because distortion is often a clipped signal or a smooth
sinusoidal waveform with the top chopped off leaving very sharp
corners that now approximates a square wave containing excessive
amounts of unwanted harmonics, which is very unnatural.
Our ears and brain are not designed to deal with such waveforms
for extended periods of time. If responsibility and care is not
brought to bear on the situation, the whole industry is going to
be faced with draconian level legislation where in fact the real
culprit is distortion.
REDUCED TO SUBTERFUGE
Some of the worst offenders are clubs. I think I have only encountered
a minority of DJs in my entire life who didn’t run the outputs
of their mixers solidly into the red and There’s not much
you can do with the signal after that. Engineers are thus reduced
to subterfuge and doctor the controls/ meters so that even when
they are solidly into the red the output signal is still reasonable.
In my mind, distortion means twisting away from truth. Distortion
is the opposite of fidelity and is alarmingly easy to end up with.
It comes in many varieties and can be introduced at any point in
the signal path. A common event is over-driving either the input
or output levels as in the previously mentioned example. Another
is the source material itself.
A more recent introduction is the horrible result from inadequate
A to D and D to A. This has spawned an industry wide revival in
valve-based processing products. Certainly, the early samplers were
a glaring example of this.
But all these points can be summed up as involving the maintenance
of signal path integrity. I have left the most damning example of
distortion introduction to last, which is of course the famed loudspeaker.
Notwithstanding operator abuse, the intrinsic distortion figures
of loudspeakers working at just 10% of their rated power (when does
that happen in real life?) dwarf anything that can be found
in other parts of the signal path that are not being overdriven.
There are, it should be noted, some very guilty loudspeakers out
there.
|
Distortion
Truths
