Live Sound University Article Fri, September 05, 2008

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.

ODD HARMONICS

Loudspeakers can introduce distortion with harmonic resonance, which can sometimes be greater than the fundamental. Odd harmonics seem to be musically worse than even harmonics. And neither is obviously best.

Another common occurrence is ringing, which is basically the cone or diaphragm that carries on bouncing around long after the original signal has ceased. The cure for this is more dampening. However, the most frequent source of distortion is over-driving the loudspeakers.

I’m not talking about giving them more watts than their voice coils are able to handle temperature-wise, but the sheer inability of most loudspeakers to deliver clean sound at just 50% of their rated power, bearing in mind how large the harmonic distortion numbers are at the AES standard of 10% of rated power.

And whilst I am on this subject, I really must take extreme exception to probably the most ridiculous measurement parameter that has been introduced in the last 20 years, namely the terminal SPL figure. This is a function of power rating, sensitivity and power compression. Taking into account the above points, 100% power input into a loudspeaker is going to result in the most dreadful audio and therefore is completely irrelevant.

In contrast, I cannot help but notice a dearth of published distortion figures for most speaker systems now on the market. This wasn’t the case in the past, so I am concluding that in fact the business has in some respects gone backward, and there’s a general tacit agreement not to publish these embarrassing specifications anymore.

TORRENT OF NOISE

The difference between clean, well-defined sound and the all-too-frequent torrent of white noise cannot be over emphasized. Firstly, working in the usual stereo mode, the producer will have the instruments mapped out on the sound stage. In the multidimensional internal listening space, the separation and placement of these instruments will be apparent and easy to find. Distortion prevents this subtle, mental reconstruction process by changing the audio information.

While this is bad enough on its own, what’s even more important is the fact that the ugly sound literally drives you away, much like your desire to leave the company of an aggressive and vexatious person. There is no way under these conditions that you are going to open your mind to the possibilities of a multi-dimensional sound stage inside your head.

But I am beginning to realize that there are many so-called audio engineers who have lived with awful sound systems for so long that they have no idea what I am talking about. You know the kind of people I mean the ones who say, “Make their ears bleed.” Crushing level is absolutely NOT what the audio experience is about. It IS about internal space. Anyone who really knows will understand that a righteous audio experience is akin to meditation.

A yet further aspect of this is the complete abuse of fee-paying audiences with horrendous sound. Let’s remember that being able to enjoy music, nay sound, is one of our freedoms, and it breaks my heart to see it so consistently abused and misapplied. 

From his early steps with his live sound rental company to his current involvement in the evolution of loudspeaker engineering, Tony Andrews has a maintained a consistent focus on maximizing efficiency and optimizing the conversion of amplifier energy into acoustic energy. He also digs windsurfing.