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Q. Can I get rid of string buzz?

By Hugh Robjohns & Mike Senior

I've got a recording of an acoustic guitar that I'm loath to re‑record, but there are several sections in which string buzz is clearly audible. Can I remove this with a bit of clever processing?

Mike Fenton, via email

SOS contributor Mike Senior replies: As far as after‑the‑fact mix processing is concerned, I'm not sure I can think of any decent way to remove string buzz, I'm afraid. The problem is that, unlike a lot of other mechanical noises the guitar makes, there's not really any way to get independent control over it with normal plug‑in processing. (I suspect that even high‑end off‑line salvage tools such as CEDAR's Retouch might struggle to make much of an impact with this, in fact.) In the case of pick noise, for example, the transient nature of the noise means that it can be effectively targeted with transient‑selective processors such as SPL's Transient Designer or Waves' TransX Wide. For fret squeaks you can use high‑frequency limiting, or simply an automated high‑frequency shelving EQ to duck the high end of the spectrum briefly whenever a squeak occurs, because such noises are usually brief and occur as the previously played notes are decaying (therefore having less high‑frequency content to damage). String buzz, on the other hand, isn't transient by nature and usually happens most obviously at the beginnings of notes, where the noise spectrum is thoroughly interspersed with the wanted note spectrum.

 
It's relatively difficult to fix fret noises with processsing, due to the very specific nature of the transients produced. For this reason, it's always advisable to record several takes of an important guitar part.

All is not lost, however, because you still may be able to conjure up a fix using audio editing if your recording includes any repeated sections and the string buzz isn't common to all sections; you may be able to just paste clean chords or notes over the buzzy ones. The main thing to remember is to try to put your edits just before picking transients if possible, to disguise them, but you should also be careful that all notes sustain properly across each edit point too, because you may not have played exactly the same thing every time. If you know that string buzz is a problem for you, I'd recommend doing several takes of guitar parts, as this will increase your editing options. If the guitar part is important enough that a bit of string buzz really matters, you should probably be comping it anyway, to be honest, if you're after commercial‑sounding results.

Published February 2011

KORG HAVIAN30 Artistry meets exploration

Q. How can I prevent feedback?

When setting up for a gig we always suffer really bad feedback from the singer's mic. We've tried positioning things differently, but it doesn't seem to help. We're pretty new to this; how can we counteract feedback?

Jo Ellison, via e‑mail

SOS Editor In Chief Paul White replies: Acoustic feedback is caused when sound from the speakers gets back into the microphones at a high enough level to cause the signal to keep increasing. This produces acoustic feedback as the signal cycles round and round the system. Positioning the main speakers well in front of the vocal mics and aimed so as to minimise the amount of sound bouncing back into the microphones will help, but there are other issues to consider. For example, if the wall behind the band is hard, it will reflect more sound back into the live side of the microphones. Imagine the room is made of mirrors and it'll be easier to establish where the problematic reflections are likely to come from. If you can hang up a thick fabric backdrop, it will help, as will positioning the main speakers so that most of the sound goes into the audience, and as little as possible points toward the walls and ceiling.

Feedback always starts at the point where the gain is highest and where the phase of the audio picked up by the mic reinforces what is coming from the speakers. If you apply EQ boost, there's more likelihood that feedback will occur at the boosted frequency, as that's where the gain is highest, but the same applies to microphones and PA speakers that have significant peaks in their frequency response curves. Choosing good-quality mics and speakers might help to minimise the risk of feedback. A mic with a gentle presence peak should be OK, but some cheaper mics have very pronounced peaks that can cause problems. You also need less gain if the singer has a naturally loud voice, so those with quieter voices need to work close to the mic. Quiet singers who stand back from the mic have no chance in smaller venues, where mics are invariably closer to the speakers than is ideal.

Stage monitors can be particularly problematic when it comes to feedback, so it pays to spend a little more on monitors that have a reasonably flat response. You also need to ensure monitors are aimed toward the least sensitive part of the vocal microphone, which, for a cardioid pattern mic, is directly from the rear. You may need to angle the back of the mic downwards to achieve this, but it will help. Hypercardioid mics, on the other hand, tend to be least sensitive around 45 degrees off the rear axis, so aim the monitor there.

 
The area directly behind a cardioid mic is the least sensitive, so positioning stage monitors there will reduce the risk of feedback. However, if you're using a hypercardioid mic, this is true of the area at a 45‑degree angle to the rear axis.

 

A third‑octave graphic EQ can help pull down troublesome peaks, but the type you find built into mixers, with only five or six bands, isn't very useful for dealing with feedback, as they change too much of the wanted sound. They can help balance the overall room sound, but that's about it. A better solution may be to connect an automatic 'feedback eliminator' hardware device to the mixer output. These are set up during the soundcheck by turning up the mic gain until feedback occurs, at which point the device measures the frequency and sets up a narrow filter to pull down the gain at that frequency. Most have several filters that can lock onto the main feedback frequencies, and they can help you gain a few more dBs of level before feedback becomes a problem. As the filter bands are so narrow, they have little effect on the overall sound. Most also include roaming filters that can lock onto feedback that occurs during performance, as it might if the singer moves the mic around.

 
Small venues of the type that so many up-and-coming bands play definitely make the fight against feedback harder, as they provide fewer opportunities for optimum positioning of PA speakers. 

Finally, when setting up levels, establish a maximum safe vocal level, leaving a few dBs of fader travel in hand, rather than working right on the edge of feedback where the sound is ringing all the time. Then set up the level of the back line to match the vocals. It's no good setting up the backline first and then expecting the vocals to match it, because in most small venue situations the vocal level is the limiting factor. You'll also find that some venues are inherently worse than others for feedback and you just have to live with it.

Published August 2010

Q. Should I be mixing in mono?

By Hugh Robjohns & Mike Senior

I've read a lot of articles about the benefits of mixing in mono. So is pressing the mono button on your DAW's stereo output and turning off one of your stereo monitors the way to go? I've had a quick go from one speaker and mono switch, but it was a bit of a mess, to be honest! I've also read a lot on panning in mono, but I didn't think this would work.

Is it better to record in mono, pan, add effects, and mix to a single stereo master? The reason I ask is that when we recorded everything in mono it seemed to sit better than many stereo files fighting in the mix.

Via SOS web site

SOS Technical Editor Hugh Robjohns replies: There certainly are some advantages to mixing in mono. The main reason for checking the derived mono from a stereo mix is to make sure it still works for mono listeners, and there can be a lot of them. For example, a lot of portable radios are mono and all car FM radios automatically switch to mono whenever the signal suffers multi‑path problems or receives weak signals, which is surprisingly often in most places. Many clubs also play music in mono, and sometimes Internet files are converted to mono to reduce data bandwidth, or become near‑mono just because of the chosen codec.

So checking that the mix works in mono is a very sensible thing to do, and if you're going to do that, it is infinitely better to check mono on a single speaker, rather than as a phantom image across a stereo pair of speakers, because the latter over‑emphasises the bass end and stimulates more room reflections, which can be distracting and affect the perceived mix.

But what about mixing in mono? Well, it's generally much harder than mixing in stereo, but you'll get much better results for your effort. The fact is that when you mix in mono you can really only separate different instruments by using differences in their relative levels and spectral content. So achieving the right balance and applying the right EQ to separate sources, becomes a lot more critical: that's why it feels harder to do. But when it's right, it is very obviously right.
 
Even now that we have hi‑tech digital radio, a lot of listeners are still hearing a mono mix, as is the case for users of the Pure Evoke radio, currently one of the best‑selling DAB radios.

Conversely, when mixing in stereo you have the same level and tonal differences to help make the mix work, but you also have spatial position (panning). By panning sounds across the stereo image, you can make the mix sound great very easily, even if you have several near‑identical‑sounding sources. Yet, when that great‑sounding stereo mix is collapsed to mono, you will often find it no longer works, because those sources occupy the same spectrum and end up trampling all over one another.

However, if you can get the mix to sound good in mono first, it will definitely sound great in stereo too. I find it a lot easier and more satisfying to work in that way, although that's possibly partly to do with my formative BBC days working in mono. If you create the stereo mix first, it can be very frustrating afterwards to have to make it work in mono too.

Of course, the only problem with mixing in mono is what happens when you come to pan sources to create the stereo image. Panning a source will inevitably change its relative level in the two output channels. Depending on the panning law in use, this may also, therefore, affect the mono mix balance slightly. Since the mono balance is inherently more critical than the stereo balance, the result is that you end up having to work around the loop a few times. For example, you set up the initial mix in mono by adjusting the fader levels and, possibly, also using EQ to ensure each source occupies its own spectrum and doesn't trample over anything else. You then switch to stereo and pan the instruments to create a pleasing stereo image. This will usually modify the balance slightly, although you are unlikely to notice anything significant while listening to the stereo mix; it will still sound great. You then switch back to mono and, if you notice the mix has gone 'off' slightly, you can fine‑tune the fader positions to get the mix balance perfect once more.

Finally, check once again in stereo and print to master tape (or whatever!). In some descriptions of mono mixing, you'll come across the idea of finding the spatial 'sweet spot' for a source by adjusting the pan pot, while listening in mono. However, this is, quite obviously, completely bonkers! What you're doing in this case is fine‑tuning the mono mix balance by using the pan pot as an ultra‑fine fader, trimming the signal level by very small amounts. Sure, it may well make it easier to fine‑tune the mono mix, but there probably won't be much sense in the stereo image positioning when you finally do come to check the stereo mix. It's obviously far better to pan the sources while listening in stereo, so you can position them precisely where you want them, then revert to mono and fine‑tune the fader positions, if necessary, to make the mono mix work as well as it can.

Reverbs and some stereo effects can be tricky when you're trying to find a perfect balance in both mono and stereo. Almost all reverbs will sound much drier in mono compared to stereo, and so, usually, some compromise will be needed. If you adjust the reverb for a good sense of space or perspective in mono, it will often end up sounding a little bit too wet in stereo (although some people like it that way), and if you get the reverb sounding right in stereo, it will often end up a little too dry in mono. There's nothing you can really do about this; it's a fundamental issue with the way most reverbs are created and the way stereo works.

Narrowing the reverb width can make the differences less obvious — and some reverbs have a parameter to enable you to do this — but it also makes the reverb less spacious‑sounding in stereo. Some mix engineers like to pan mono reverbs with each individual instrument to try to maintain a better stereo‑mono balance, but it's a lot of extra work and I'm not convinced it sounds that much better anyway.

Published February 2011

Korg Pa-series Songbook and Songbook Editor Software

Q. Can I get rid of string buzz?

By Hugh Robjohns and Mike Senior

I've got a recording of an acoustic guitar that I'm loath to re‑record, but there are several sections in which string buzz is clearly audible. Can I remove this with a bit of clever processing?

Mike Fenton, via email

SOS contributor Mike Senior replies: As far as after‑the‑fact mix processing is concerned, I'm not sure I can think of any decent way to remove string buzz, I'm afraid. The problem is that, unlike a lot of other mechanical noises the guitar makes, there's not really any way to get independent control over it with normal plug‑in processing. (I suspect that even high‑end off‑line salvage tools such as CEDAR's Retouch might struggle to make much of an impact with this, in fact.) In the case of pick noise, for example, the transient nature of the noise means that it can be effectively targeted with transient‑selective processors such as SPL's Transient Designer or Waves' TransX Wide. For fret squeaks you can use high‑frequency limiting, or simply an automated high‑frequency shelving EQ to duck the high end of the spectrum briefly whenever a squeak occurs, because such noises are usually brief and occur as the previously played notes are decaying (therefore having less high‑frequency content to damage). String buzz, on the other hand, isn't transient by nature and usually happens most obviously at the beginnings of notes, where the noise spectrum is thoroughly interspersed with the wanted note spectrum.
 
It's relatively difficult to fix fret noises with processsing, due to the very specific nature of the transients produced. For this reason, it's always advisable to record several takes of an important guitar part.

All is not lost, however, because you still may be able to conjure up a fix using audio editing if your recording includes any repeated sections and the string buzz isn't common to all sections; you may be able to just paste clean chords or notes over the buzzy ones. The main thing to remember is to try to put your edits just before picking transients if possible, to disguise them, but you should also be careful that all notes sustain properly across each edit point too, because you may not have played exactly the same thing every time. If you know that string buzz is a problem for you, I'd recommend doing several takes of guitar parts, as this will increase your editing options. If the guitar part is important enough that a bit of string buzz really matters, you should probably be comping it anyway, to be honest, if you're after commercial‑sounding results.

Published February 2011