Cable Sounds and uk.rec.audio

Arguments about the ‘sound’ of audio cables crop up with monotonous regularity on the uk.rec.audio newsgroup (and elsewhere!). Usually, this arises when someone posts a message claiming that they can hear “obvious differences” between one cable and another. This then prompts responses which challenge/doubt/attack/dismiss the claims. The resulting posts then usually go over much the same ground as on many previous occasions. Sometimes venomous arguments develop which do not really help to clarify the matter.

The purpose of this webpage is to summarise some of the basic, recurring, points that I would personally tend to make in such discussions, so as to avoid having to re-write them on each occasion. I hope that what follows will be useful as a summary/reference for those involved on uk.rec.audio and elsewhere. It should serve as a start-point and avoid the need to make the same points repeatedly on the newsgroup.

Set of basic comments

With the exception of a few specific situations (detailed later) the following comments can be made with regard to the argument about ‘cable sound’ in audio:

1) That arguments about this have now been proceeding for some decades in the audio magazines, and for some years on newsgroups like uk.rec.audio. But during this period the following statements have – so far as I know – applied.
2) That none of those who say they can hear such audible difference have ever been able to establish in a suitable test that they can tell one cable from another when the only way available for them to discriminate was the sounds.
3) That the ‘explanations’ given by cable makers, sellers, and in audio magazine reviews tend to be either technobabble, or exploit points by exaggeration or by taking them wildly out of context. Thus no reliable theories or explanations for the claims have been established which would be accepted by most professional physicists and engineers.
4) That I, and many others, simply do not hear these claimed differences, despite having repeatedly attempted to do so.
5) That – although a succession of people have appeared on uk.rec.audio and claimed they can hear ‘obvious differences’ – they then generally refuse to participate in a test whose outcome would have the ability to either support or confound their claim with some measure of reliability or statistical significance based solely on the sounds.
6) That – although makers, sellers, and magazine reviewers often publish material which asserts and comments upon such ‘sounds’ – to the best of my knowledge none of those involved have ever shown in a test of the kind referred to in (4) that they can actually tell one cable from another solely on the basis of the sounds produced. Indeed, when makers, sellers, or reviewers have been invited to participate in such a test, the standard reaction seems to be to refuse and simply insist that they ‘know’ the can tell the difference. Thus avoiding the risk that a test might show they were unable to actually do so on a reliable basis.

Exceptional cases

There are some specific situations where swapping one cable for another may well cause an audible change to the sounds produced by an audio system. These may be summarised as below, and can be regarded as exceptions to the above. In these exceptional cases there are well-known reasons in terms of the relevant physics, etc, to expect and audible effect when one cable is replaced by another.

1) The frequency response may be altered as a result of the output resistance of a source unit (CD player, tuner, etc) interacting with the shunt capacitance of the cables used as ‘interconnects’ to link them to an amplifier. This combination acts as a low-pass filter and may slightly reduce the level of high treble.

Typically, co-axial cables used for domestic audio have shunt capacitances in the range from 50 to 500 pF per meter of cable, and are less than a couple of metres in length. Typical sources have output impedances in the range 50 - 500 Ohms. What matters here is the product of these values. (This is covered in more detail on the Analog and Audio pages of the ‘Scots Guide to Electronics’.)

Taking as an example a ‘worse case’ from the above ranges we can say that a 1 metre interconnecting cable having 500 pF/m, combined with a source impedance of 500 Ohms produces a low-pass filter effect with a -3dB point at 630 kHz. The change at 20 kHz is around 0·005 dB. This is so small that it seems unlikely to be audible. Hence in most cases this effect should have no audible consequences. However, if the system is unusual and includes an exceptionally high source resistance and/or a cable of exceptionally high capacitance then the result may be an audible when one cable is changed for another of different capacitance.

There are two specific well-known cases where such an effect is more likely to arise:
- Where the signal source is a Moving-Magnet (MM) pickup cartridge as used to play Vinyl LPs. Many types of MM cartridge (e.g. those made by Shure) have characteristics that means their output frequency response is very sensitive to the capacitance of the cables used to connect the cartridge to the RIAA/phono pre-amp. Hence when using such a cartridge, we can expect the capacitance of the connecting cables used to have a noticeable effect. Indeed, Shure and other makers recommend a specific amount of ‘load capacitance’ which should be used for optimum performance.
- When the source component uses valves (vacuum tubes) as the output devices and/or has low internal feedback. This may result in particularly high output impedance for the source component. Hence making an audible effect more likely than is the case in general.
2) The frequency response may be altered as a result of the series resistance and/or series inductance of the loudspeaker cables interacting with the loudspeaker’s input impedance. I have examined this effect in more detail in the Analog and Audio pages. It seems more likely to arise in domestic systems than (1) unless the cables are chosen with low resistance and inductance in mind. For domestic cable runs of a few meters it is quite easy to obtain cables with suitable low series resistance and inductance so as to ensure this is unlikely to have an audible effect. However the effect can be audible in some circumstances, depending on the type and length of cables, and the loudspeakers employed. In particular, audible effects due to this are more likely with loudspeakers with an impedance that drops to a low value at some frequencies in the audio band - e.g. electrostatic speakers like the QUAD ESL57.
3) Some designs of Power Amplifier (and in some cases a faulty amplifier) can produce parasitic oscillations or become unstable when used with some cables. Typically with loudspeaker cables that have a relatively high shunt capacitance. Most professional or commercial modern designs of amplifiers should not show this problem under any domestic circumstances if used as intended. Hence this should not be a problem. However in some cases it may occur, and will alter the performance of the amplifier, than thus may have an audible effect.
4) Poor connections may produce ‘non-ohmic’ contacts. These can act as non-linear devices in the signal path, and create distortion. The typical cause of this is dirty or tarnished surfaces of pugs or sockets. In some cases a soldered or wrapped joint may also become non-ohmic. These distortions can become audible.
5) Some cables may provide poor levels of screening or earth return. This may lead to problems due to hum loops or interference. This may be audible in some way, or may upset some of the associated equipment in the audio system, thus altering the sound.

Each of the above represents in engineering terms a well-known effect that can be measured and avoided. Hence they are not regarded as contentious. In general, the above situations would tend to be regarded by engineers as a fault or imperfection in the system/cable that should be dealt with and removed. For these reasons if someone on uk.rec.audio says that they doubt that a change of cable will physically alter the resulting sounds, then the above cases may regarded as being exceptions to that statement.

As a result, arguments about ‘cable sounds’ should be limited to situations where it is established or agreed that the situation is such that none of the above are likely to be the cause of a claimed alteration in the sound when one cable is replaced by another.

Assessing claims

Given the above, I, and various others on uk.rec.audio, rather doubt (excluding cases covered by the exceptions described below) that the claims made are reliable. Speaking personally, I regard it as a pity that people make the claim, and then refuse to put it to a suitable test. As a physicist/engineer I’d love to discover that audible ‘cable sounds’ arise which were not due to one of the above exceptions. This would imply there was some ‘new’ physics to be discovered, and I would find this both interesting and exciting. I would also welcome finding that – despite my experiences to the contrary so far – that I could get an improved result by such means since I do enjoy listening to music via the audio systems I use.

I am therefore disappointed that people keep making claims, and then refuse to even try to show they can actually hear what they claim.

This refusal to engage in such a test keeps the claims to having the status of being a ‘belief’ which they hold, and expect others to accept on as a matter of ‘faith’. Hence we are unable to resolve the matter since those making the claims decline to make this possible. Yet many of us do not hear what is claimed, and when people have tried in tests, the results do not support this belief. Hence my doubts, and those of others. Again, speaking personally, I am not attracted to the idea of applying a ‘faith based’ approach to such a topic. It seems to me that the scientific method is more likely to prove useful. But can only be the case if at least some of those who make the claims are prepared to engage in suitable tests which could then provide relevant evidence, as distinct from personal opinions/beliefs.

The above does not mean I regard those making the claims as being liars or fools. Nor do I necessarily think that no audible differences can ever have occurred in at least some of the reports. If we ignore the possibility of one of the above exceptions having occurred without the claimant being aware of it, there are still many reasons why someone might come to believe that a change of cable altered the sounds, when this was not actually so. Here I can give some examples.

Physiological Effects. If we examine the research literature on the physiology of human hearing we can find measurements and other tests which show that the biomechanics of hearing are altered by various factors. One of the most well-known of these being that the sensitivity of hearing physically alters as a result of listening to loud sounds. This can change the response of the hair cells in the ears, and the output patterns sent to the brain. Some of these changes are temporary and the ears ‘recover’ after a period of minutes or hours. This means that if we listen to the same recording twice in succession, our ears may simply respond differently the second time around.

In addition to the above, becoming tired, or alert, or the diurnal cycle can alter the biomechanics of human hearing. As can illness, etc.

Psychological Effects. The most commonly mentioned effect in this class is what people call “expectation” when referring to a pre-conception that a given cable has a given effect upon the resulting sound. Put most bluntly this tends to be phrased along the lines of, “If you spend a fortune on a cable you will wish to hear an effect that makes the results sound better!”

However even if we discount the above, there is a more subtle problem. This is due to the way the music/speech used for any comparison has been chosen and used. If we use a different recording each time we changed cables, then it would become almost impossible to tell if any changes were due to the change in the recordings. Hence the tendency is to use the same set of recordings and play them via each choice of cable in turn. This nominally ensures we are comparing ‘like with like’ so far as the source material is concerned.

The difficulty with this approach is that the listener, when listening, will tend to notice particular features or details of the sound on one ‘play’, and then may find they are listening for them again the next time the same recording is played. This means they may tend to ‘focus’ on some detail and hence are listening in a different manner to the previous occasion. This tendency should be a familiar one to many people who enjoy listening to music. When we listen to music repeatedly we tend to both look for some anticipated details, and hope to discover new ones each time we listen. If the sounds are reasonably complex this means that we may mentally ‘pilot our attention’ through the music in a different manner from one occasion to another. Indeed, we may either find more to enjoy, or become bored. This implies that we are not actually listening in the same way every time, and our ability to judge what we hear is being altered by the act of having previously heard the recording.

Acoustic Effects. Slight movements of the head/ears whilst listening can also change the sound patterns reaching the ears to a significant degree. As can any movements of the speaker positions, or the opening or closing of the doors of the listening room, or movements of the furniture. Such changes are also easily demonstrated by making acoustic measurements. Even the attenuation properties of the air will vary with humidity and temperature.

Equipment Variations. It may be the case that the signal level was not kept the same during each period when cables were compared. Or, for example, that the speakers in use changed their properties as a result of being used for some time.

The above set of examples is not meant to be exhaustive or to be the ‘reason’ for all cases where people make claims. However it serves to indicate that unless great care has been taken to deal with issues like the above, that there may be good reasons to suspect that a claim that a change of cable alters the sound might actually be due to some other cause that has nothing to do with the cable as such.

Conclusions

I do not doubt that the arguments over ‘cable sound’ will continue, and people will continue to make and sell expensive cables. Some people will buy these and pronounce that they very pleased with them. Others will insist this is all utter nonsense, and that people are being deluded. I suspect this will continue until some of those making the claims actually come forwards and start participating in tests designed to resolve the issue. Until then, my personal position is to be sceptical for the reasons outlined above.