Q What made me hear a phantom low note when singing in a choir?

Sound Advice : Recording



I recently attended a choir workshop in a large, square, empty church. The space had incredible acoustics and we measured around six seconds of reverb, even with 40 people in the room. At one point, the tutor had us all stand in a circle and sing particular notes of a scale increasing in pitch at the following intervals: 1, 5, 1, 3, 5, flat 7, 1 and 2, starting an octave below middle C. We all just held an ‘ah’ sound at our given note and, very quickly, a tone two octaves below middle C was clearly audible, appearing to come from different parts of the room — it sounded like there was an invisible nine–foot man singing in the middle of us! What on earth was going on, and can it be achieved with other instruments? Can it be used in any practical way in music–making?



Hugh Robjohns



Ellen Maltby, via email



SOS Technical Editor Hugh Robjohns replies: This sounds amazing! I suspect that the note intervals generated an interference beat–tone which resonated as a standing wave within the hall — the standing wave bit seems certain given your comment about it being audible at specific places within the room. I imagine the same would be possible with anything that generated suitably sustained tones of the right pitch — relatively pure–toned instruments, rather than very harmonically complex ones.



A ‘missing fundamental’ (dotted line) can sometimes be ‘heard’ if enough of its harmonics are present.A ‘missing fundamental’ (dotted line) can sometimes be ‘heard’ if enough of its harmonics are present.Could it be practical for music-making? If it’s related to standing waves, then it will be totally building specific, in which case it might be useful for a piece that will only ever be performed in the one place, but it would fail if performed elsewhere (assuming it didn’t match the precise dimensions). I have in the back of my mind that some monastic choral music only works in the monasteries where it was written — and that may be for similar reasons... or that might just be the random regurgitations of a befuddled mind!



SOS contributor Mike Senior adds: I’d agree with Hugh that acoustic interference effects almost certainly play an important part in creating the ‘phantom bass singer’ you heard. In other words, the frequency differences between note fundamentals are creating interference ‘beats’ at frequencies in the audible spectrum — in your specific case at a frequency of around 65.5Hz for C2 (two octaves below middle C). The chord you mention provides maximum opportunity for this, because it neatly arrays the fundamental of each note 65.5Hz apart from both its neighbours — assuming, that is, that the choir are singing unaccompanied and tuning amongst themselves by ear, using what we call ‘just’ intonation rather than the equal–tempered intonation used by most keyboard instruments.



However, the acoustic aspect of this effect was probably only part of what you heard. A very similar phenomenon has been demonstrated to occur within the physiological apparatus of the inner ear (so it doesn’t rely on tones mixing in the air), as well as entirely as a perceptual illusion (difference tones can be created even between sounds fed independently to separate ears over headphones — fairly freaky if you think too hard about it!).But why do you hear this added tone as forming part of the choir, rather than as some kind of separate note? I think this has something to do with the ‘missing fundamental’ effect, whereby we judge the pitch of a note according to its fundamental frequency, regardless of whether we can actually hear the fundamental. In other words, we’re very adept at perceptually extrapolating what a note’s fundamental should be even when we’re only presented with the upper partials of that note’s harmonic series. A common audio–engineering ramification of this is that we can still recognise low–pitched notes when they’re coming through a small speaker that could never produce their fundamental frequencies.In your situation, I reckon that your brain is (incorrectly) identifying the presence of a C2 note within the choir texture, simply because so many of the important frequency components of that note’s harmonic series are present. Your perception is filling in the missing fundamental, making it appear as if there’s someone in the choir channelling the spirit of Barry White!So what can we use this effect for? Not much, to be honest, simply because you need a stack of quite pure tones in ‘just’ intonation to create appreciable difference–tone levels, and the appeal of that kind of chordal texture is fairly limited, not least because most Western music is based around the deliberate tuning impurities of the equal–tempered scale. Plus, the relationship between musical intervals and the difference tones they generate is rather counter–intuitive from a musical perspective — whereas a C3–G3 interval produces a difference tone at C2, the C3–F3 and C3–A3 intervals give, respectively, difference tones a fifth below (F1) and a fourth above (F2). In practice, this pretty much rules out using difference tones creatively for most musicians, unless your music–making tends to involve burning a lot of incense. In fact, the most practical application of the idea I’ve discovered is where some church organs use difference tones (termed ‘resultant tones’) to mimic the effects of deep–pitched pipes that would be physically too long to install.    

Published in SOS February 2015

KORG ALL ACCESS: Wilco's Nels Cline brings the KAOSS

Q What gear should be burnt in before use?

Is ‘burning in’ studio equipment (monitors, headphones, tube gear, and so on) of benefit to certain types of studio gear, or is it all just Internet hype?



Hugh Robjohns



El Bungle, via email



SOS Technical Editor Hugh Robjohns replies: This is a widely and hotly debated topic which usually creates very polarised views. For the uninitiated, ‘burning in’ is claimed to be the electrical equivalent of ‘running in’ a car engine (not that it is necessary to do that any more); a process intended to help the device in question ‘settle down’ into its normal working condition, usually with claims of significantly better audio performance as a result.



Putting the better-performance argument to one side for a moment, the one inevitable aspect of burning in is that it will happen anyway as the equipment is used, so whether it’s a genuine phenomenon or not, all equipment will inherently become run–in quite automatically. We have no choice in that. I’d therefore suggest that it’s not something that warrants any real concern or effort in the vast majority of cases.



Returning now to the ‘better performance’ argument, my personal view is that there is credible science to explain why the technical performance might change during the initial period of use in some very specific cases, and I’ve personally experienced persuasive first–hand evidence of burning–in on several occasions. In general, though, I think many of the claims are little more than a misguided explanation for a period of increasing familiarity with the sonic characteristics of a new piece of equipment.



When opening the box of your latest swish reference headphones, should you suspend your excitement until you’ve broken them in? We can emphatically say... ‘definitely maybe’!When opening the box of your latest swish reference headphones, should you suspend your excitement until you’ve broken them in? We can emphatically say... ‘definitely maybe’!The specific cases I mentioned apply predominantly to the performance of some power–handling electro–mechanical transducers — by which I mean loudspeakers of various types. The technical parameters of some drive units can change slightly during their initial use because of the way the various materials employed in their construction flex and move, and the glues and dopes cure over time. To illustrate this concept in an everyday scenario, I’m sure we’ve all experienced the way in which formal leather shoes soften and become more comfortable after some use, for example.



The question of whether such drive-unit parameter changes become audible or not will depend entirely on whether those parameters play a critical part in the whole design’s overall performance. In some designs, a 10 percent change in compliance might have a very noticeable effect, and in others it might remain completely inaudible but, for the record, I’ve personally witnessed the effect of drive unit burn-in with various monitor loudspeakers. To put it into context, I’ve auditioned countless more monitors that appeared to have no burn–in effect whatsoever. I’ve also heard the effect first–hand once or twice with some types of high–quality headphones, too, but I should point out that I am in the unusual position of being able to make direct comparisons of brand-new and run–in products more easily and more often than most consumers.



When it comes to straightforward electrical components, like cables, the concept of burning in makes no sense whatsoever to me, and I can’t say I’ve ever noticed any kind of cable burn–in effect. I’ve never noticed it with electronic hardware either, whether it’s solid–state or thermionic (ie. valve) gear — although I have most definitely heard the effect of temperature variations in some electronic equipment as it warms up to a normal operating temperature. Again, the performance of some equipment might be temperature dependent, and other designs not at all, but this might be something which could well be mistaken for burning in.



Importantly, burning in is something which can only ever happen during the first few hours of use, and most electronic hardware manufacturers run ‘soak testing’ as part of the factory’s quality–control testing process. This is where the device is left powered–up for hours or days to test for early electrical component failure, because statistically it is most likely that a new product will fail very soon after manufacture. If it doesn’t fail in the first few hours or days, the chances are it will work reliably for a long time: a graph of failure rate versus time is known in the industry as the ‘bathtub curve’, because the failure rate drops steeply after manufacture to settle at a low rate, before eventually rising again as components reach the end of their working life! However, soak testing tends not to be applied to electro–mechanical devices, and perhaps that’s another reason why the effect of burning in is more likely to manifest with these devices than electronic hardware.



I take an entirely pragmatic view to burning in. If a brand new product doesn’t sound entirely right when I first start using it, I just leave some audio running through it and go off and do something else for a while instead. If it sounds better when I return, it may have completed a burn-in process or maybe I’ve just become used to it! And this last point is not meant to be as flippant as it sounds — there’s no doubt at all that we become familiar with the characteristics of things over time, and any change from that familiarity immediately seems wrong, until we become familiar with the new condition. Try altering the angle slightly of the seat backrest in your car, for example. Initially it will seem ‘wrong’ but after a week it will feel entirely normal, and resetting it to the original position will then be ‘wrong’! That process of becoming familiar with a new condition, or new sonic characteristics, may well be what some claim to be the burning–in period — but it’s the listener that’s actually ‘burning in’ rather than the equipment itself!    

Published in SOS December 2014

Q When and how should I use reference tracks?

Sound Advice : Maintenance




I keep reading that it’s a good idea to use reference tracks when mixing, but when should I be referencing other mixes — and what exactly is it that I should listen for?



Mike Senior



Jim Dodd, via email



SOS Contributor Mike Senior replies: Referencing your work in progress against commercial mixes is something that you might do at any point during the mixdown stage, in order to give your ears and brain a more objective benchmark when you’re making critical mix-balancing decisions. However, in my experience it’s easy to lose track of your own vision for the music you’re working on if you reference every little mix move you do, so in practice I’d normally only pull out the comparison CDs under the following circumstances:



Just before the mixing session, or during breaks.

When you’ve got a decent static mix balance sorted out.



In the first case, the purpose of the referencing isn’t anything specific. It’s mostly just to recalibrate your ears to known material, so that you head off any obvious problems in good time: for example if you’ve just dialled in too much low end overall, or you’re mixing a bit too wet in general, or you’ve massively overcooked your hi–hat levels.



We’ve written many times in the magazine about the importance of sifting through your CD collection for high–quality reference mixes. But precisely when and where should you use them to best effect?We’ve written many times in the magazine about the importance of sifting through your CD collection for high–quality reference mixes. But precisely when and where should you use them to best effect?It’s only in the second scenario that it’s worth bouncing out a mix in progress, and then lining it up alongside your reference material in a fresh DAW project. Here, you’re much more concerned with how specifics of your mix relate to the reference material, so you need to ask yourself some questions. Is the balance sensible? Is the stereo image wide enough? How much low end am I using, and how does that compare with the market I’m aiming the mix at? This is one of the most difficult parts of any mix, in my opinion, because you can’t just ‘photocopy’ the mix sound of the references, because they’re never exactly the same as the music you’re working on. You have to listen to the range of answers each mix offers for each mixing question, and then decide where you place yourself in relation to those. One mix might have more snare level than another, say, so you have to decide whether you match either of them with your own snare level, or split the difference between them somehow, or maybe deliberately take a more extreme stance. The point of referencing is that you make those kinds of decisions in as informed, and repeatable, a way as possible. Then when the artist says “there’s too much bass” you’ll have something sensible to say to them on the subject other than “but I liked that much bass”!



Referencing isn’t just useful for mixing, though, because it can also help to keep you from misjudging many aspects of a recording while tracking, especially when you’re working on location with monitoring equipment you’re not tremendously familiar with. A few minutes spent referencing some of your test recordings against commercial material can head off all sorts of problems that would otherwise require time–consuming remedial mix work later on — especially if you’re trying to judge bass levels and/or stereo width on headphones.    

Published in SOS December 2014

From The Vault: Introducing the PA1X and PA1X Pro!

From The Vault: Conozca el PA80

Q Should I buy my own digital mixer for a band tour?

Sound Advice : Mixing



I’m the sound engineer with a group called Flyte, who are heading out on a mini headline tour of 150-500 capacity venues next month. I have the chance to acquire a little digital mixer such as a Behringer X32 rack, but I’m not sure if it would be worthwhile. Obviously I’m trying to weigh all the factors, like having a lovingly pre-sculpted FOH and in-ears mix to start every day with, versus the ball-ache of crow-barring the mixer into tiny booths in the face of reluctant in-house guys. Any advice on this would be gratefully received.



Hugh Fielding via email



SOS contributor & the Prodigy’s live-sound engineer Jon Burton replies: In an ideal touring situation you’d carry the same equipment to every venue to ensure familiarity — and thus speedy operation. If you have a mixer you know well, and which is already configured with the basic settings you need to start the day, you’ll save a lot of the time you’d otherwise take setting up a house desk, configuring the monitors and generally wiring it all up. That frees up more time to consider the ‘variables’ in each venue — the house sound system, the amps and speakers, the unique acoustics. Don’t underestimate that, as getting the house system sounding good, and everything working correctly, can often take up a lot time.



However just turning up with your desk is only a small part of the answer — you must also consider the infrastructure that supports that desk. Having your own gains set in the mixer is only any use if you are using the same sources, for example, and this means not only the instruments, but also the various microphones and DI boxes that feed their sound into your desk. You can buy a reasonable 32-channel desk for very little,With sophisticated digital desks becoming ever more affordable, it seems tempting for the small touring band to invest. It may be the right solution, but there’s an awful lot more you need to think about than acquiring the desk!With sophisticated digital desks becoming ever more affordable, it seems tempting for the small touring band to invest. It may be the right solution, but there’s an awful lot more you need to think about than acquiring the desk! but buying all the microphones to go with it may cost you the same figure again and more.



The next stumbling block is carting all those mics around with you on tour, and then, of course, you have to have a means connecting them (placed somewhere on the stage) to your desk, which might be quite some distance away. There will be an in-house multicore which will go from the stage to the house desk, but using this is fraught with difficulties. Will there be enough channels in each and every venue? If so, do they all work? How is the cable terminated at the desk end? Will the leads be long enough to go to your desk? Is it a digital or analogue cable run? And so on...



As you point out, you might also run into space issues. With smaller venues, the mixer tends to be shoe-horned into a very small area, probably leaving very little space for your desk. Will you be able (or indeed allowed) to move the house desk? If you do move the house desk, who will mix the support band, and on what? If you move the multicore to your desk will it have to be patched back for the support act — and if so, who will do the re-patching of the 20-plus channels you’re using in the 15 minutes between bands when you are needed on stage to reposition microphones? It’s a lot to ask of anyone, and introduces unnecessary risks.



For all these reasons, if using your own desk, it’s usually best to also take your own multicore and stage box, so that you can be completely independent of the house system. This way you can just give the house engineer a left/right mix that he can run into his desk and into the house system. Great! Except now you need to spend money on a multicore and stage box. An analogue one will be big and heavy, but relatively inexpensive, whereas a digital one will be small and lightweight, but expensive. You’ll probably need some sub boxes or looms for the drums as well, to save you time and effort.



By now you have easily spent triple the cost of your desk alone, and have gone from a little mixer to a small touring package. You’ve also started taking up a lot more room in the backline van. By bringing in your own desk and cables you’ve also reduced the job of the house engineer to lending you a few mic stands and giving you two channels of the house desk for your mix. My experience of touring at this level (more times than I care to mention) tells me that the house engineer will be delighted; rather than jump in to help set up an unfamiliar system, he’ll probably slink off to his warm cubby-hole for a refreshing cup of tea while he imagines how you’ll end up ‘hoist with your own petard’!



Having said all this, if you can live with the budget, the risks and the inconveniences described above, a package like this can be fantastic for this sort of tour — but only if you prepare properly. Don’t turn up to the first show at three in the afternoon thinking you can just throw it all together! You need to be there in rehearsals with the band, doing a dry run. You need to label cables and boxes, check that the leads reach right across larger stages, and that everything works as it should. This is the role of the production rehearsal, and it’s best done with the band set up just as they intend to play live. You can then make up time-saving looms and label them clearly so everything can be interconnected easily and quickly.



If you’re creating in-ear monitor mixes, this level of system really comes into its own, as it virtually eliminates the variables from the stage point of view, and you’ll be ready with a basic mix straight away. One option you may want to look at is a monitor-only set up, whereby you carry a desk to use just for the monitors but use the house desk for the FOH mix. This would still involve carrying a microphone set and stage cables, and you’d need a simple microphone split system to go into the house multicore, but it can work really well, and save you a lot of time. A few times recently, I’ve seen this sort of setup but with the band themselves controlling their own monitors using iPads. Only certain desks will support this, but there are actually quite a few now, so perhaps that’s something to consider.



I know this hasn’t really answered the question — I’m afraid that you really do need to weigh up all of the pros and cons for yourself — but hopefully I’ve been able to give you a clearer picture of what you can expect when embarking on this road, and prompted you into a practical course of action!    

Published in SOS January 2015