Engineering Bass Guitars Live

They form the foundation of most bands, but getting them right can be tricky. We explore the many ways to deal with bass guitars on stage.

The bass guitar is an important part of any band’s overall live sound. Along with the kick drum, it will be the foundation of the rhythm section, but getting across the sound of the bass whilst adding weight to the overall sound can be more difficult than it would first appear. Bass players can have a wide range of sounds, from fretless jazz to rock, funk and the sonic onslaught of Lemmy. Playing styles — fingers, plectrum or slap — all come with their own problems, and in this article I will show you a few ways of dealing with them.

Direct Line

The most common way to reinforce the bass guitar is with a DI or ‘direct injection’ box. These come in two standard forms — active and passive. Passive boxes are the simplest, usually having one input, a parallel output to loop through to the amplifier, and an XLR output to go to the mixing desk. Inside, they have a transformer which makes the signal more suitable for the mic input on a mixing desk. Passive boxes are normally placed between the bass guitar and the amplifier, although some have an input that can be used after the amplifier, accepting a signal from the speaker output (rarely do these provide a load, so always make sure you are using a speaker as well). The quality of passive boxes varies enormously and is usually dependent on the transformer used inside. The best are very good and will prove incredibly reliable as there is very little that can go wrong. These boxes do not require any external power, hence the name ‘passive’.

Active boxes do require power, usually either from an internal battery or via phantom power from the mixing desk. They perform much the same task as a passive box but use active buffer circuitry instead. They range from being simple boxes similar to passive DIs, to being more complex devices with gain and equalisation. They have the advantage that they are able to deal with a wider range of levels than passive DIs, even very low ones. Once again, the quality of components and design can vary dramatically, as can the cost.

The choice of DI boxes is huge, with boutique specialist boxes now being available, such as the Ridge Farms Gas Cooker, with its distinctive oversized knobs — an incredibly warm-sounding valve-based device. There is also an increasing number of boxes that are designed to go between the amplifier and the speaker, capturing not just the tone of the instrument but also of the amplifier. Radial’s JDX and Palmer’s PDI 09 are popular choices for taking the signal after the preamp stage.

It is always worth looking at the bass amp itself, as many bass amps have a DI output in the form of an XLR socket on the back of the amplifier. If the bass amp is contributing to the bassist’s tone, this would be my first choice, as these outputs are usually post preamp, which is where most of the amplifier’s coloration will occur. These days this feature is quite common and an excellent sound can be achieved using this handy output. Some amplifiers have an option to make this DI either pre (before), or post (after) the equaliser section: there are no hard and fast rules here, but I would always get the bass player to play and get a handy third person to switch between the settings while you listen from out front.

Six Million Ways To DI

So which is best? A good passive box will be just as good as an active box and would normally be my first choice, but if there are likely to be any level problems, such as weak pickups, I may well go for an active one. My first act will be to look at the bass player’s equipment and ask them about their sound. If they have what I would call a ‘clean’ setup — an Eden, SWR or Trace Elliot amp without any pedals, say — it is usually just the sound of the bass guitar itself I will be looking for. A DI box between the bass and the amp will be your best bet at capturing the sound as closely as possible. If, however, the bass player has a valve head, like an Ampeg, Fender or similar, then they are probably using the qualities of the amp to add to the tone. Then I will look at taking the sound after the amp.

Bass players who use effects pedals are becoming increasingly common, and if the bassist is using pedals then I will definitely need to capture the sound as far down the chain as possible. The trouble with using a DI box just after a pedalboard, however, is that the effects are often mellowed by the settings on the amp, and without the EQ on the amp the sound can get fizzy. In this case, I would pay attention to the amplifier’s output first. It will, of course, come after the pedals in the chain, and will capture the sound of the effects, but will also be getting the sound of the preamp section as well.

DI boxes are most commonly connected directly to the bass, with a feed going from the DI to the amp.As with guitarists, it is also always wise to run through the various sounds that they will be using. Leaps in level caused by distortion pedals or envelope filters are common events, so it is worth listening out for these during the soundcheck.

Decisions, Decisions...

You will notice that no mention has yet been made of microphones! That’s because in many situations a DI box will actually be the best approach. For me, several factors dictate this choice. My first consideration is always sound, the second is practicality. Listen to the bass guitar and note what it sounds like: if it is a clean, ‘straightforward’ sound then a DI box is the obvious answer, as it will capture the sound of the bass guitar best, with less coloration. It is an easy and practical choice. The main advantage of the DI box is that it only picks up the sound of the guitar; there is no spill, and no chance of feedback or boominess if you add more low frequencies to the bass. However, if your bass player is using pedals, or has a distinctive amp tone, then a microphone might be your best bet...

The choice of microphone depends very much on what sound it is you want to capture, and whether it is the full frequency range or just a part of it that you’re interested in. There is no such thing as the ‘perfect’ microphone for bass guitar, because the choice is very dependant on what you are hoping to achieve. Choosing a microphone can be a complicated task, because bass guitars have a surprisingly wide frequency range. A standard-tuned four-string bass starts at 41Hz on the lowest E-string in standard tuning. If your bass player has a five-string then the lowest frequency will be around 30Hz for the low B. The sound can also vary greatly depending on the type of string (whether they are round or flat wound, nickel or nylon coated), the style of playing (fingers, pick or slap) and the type of pickups (passive or active). All these factors will affect how much low-, mid- and high-frequency information you have.

Mic Models

I will usually choose a microphone that will give me a sound close to the one I am looking for without having to add too much equalisation. If I am after a very neutral sound, as close as possible to the bass itself and with a nice extended low end, I will look first at a large-diaphragm dynamic microphone. Traditionally, this means an AKG D12 or D112, or possibly an Electro-Voice RE20. Both the D12 and RE20 were originally designed as vocal microphones, but they deal with bass very well. The RE20 is a very interesting microphone as it is not susceptible to proximity effect, so using it close up to an amp will not add any unwanted low end. This is due to a design feature that EV call ‘Variable D’: multiple sound-cancelling entrances at varying distances from the capsule combine to provide a uniform cardioid response across the mic’s frequency range. This helps to maintain a tight, smooth sound even at high levels. The D12, on the other hand, has a bass chamber to increase low end, but is also able to deal with incredibly high SPLs. More modern microphones such as Shure’s B52, Sennheiser’s E902 and Heil’s PR40 have seen designs developed especially for capturing low-end sources, whether it be kick drums or bass guitars.

Many bass amps have a DI output built in, which can be useful as it allows the front-of-house bass tone to be affected by the amp’s preamp and EQ settings.Sometimes I am more interested in capturing a part of the character of the sound rather than the full range. With some bass players low end is not the issue, it is the mids and highs that are important. If you are trying to capture a distorted bass sound, for example, then you want a microphone that is going to maintain that gritty edge.

The Beyer M88 and Shure SM57 are both good in this respect. The Beyer has a very smooth sound and a surprisingly good low end. It is not an uncommon choice on kick drum, especially for a mellow jazzy sound. The Shure SM57 has a pronounced presence peak that helps it cut through other sounds, which is perfect for the mid/top range of a distorted bass guitar.

Best Of Both?

Quite often, if I have a bass that is using a wide range of sounds, I will combine a microphone and a DI box. I will get the low end from the direct signal, and the mids and highs from the microphone. This can help to give a best of both worlds situation. Having two channels can also give you the chance to favour one sound over another, blending the mic in with the DI to add colour to the sound. I will, on occasion, roll off most of the low end of the microphone using the high-pass filter on the channel so that it is only looking at the mids and highs of the sound.

As soon as you do combine more than one source on your bass guitar, be it a DI and a microphone or two microphones, the problem of phase will rear its ugly head. The direct signal and the microphone can often be out of phase with each other. Normally this is due to the two signals looking at opposite sides of the waveform. This will result in cancellation of frequencies, which will be particularly noticeable in the low end. If both signals sound fine on their own, but the sound becomes thin when combined, then this is usually the cause. Reversing the polarity of one channel on the desk relative to the other should remedy things. Which channel you switch depends on which signal is in phase with the sound coming from the stage. I will always check the bass channel on the desk with the sound coming off stage to make sure the two are relatively in phase. I will normally stand where I can hear both the bass guitar cab and the PA system at equal levels, and get a colleague to switch the polarity button on the bass guitar channel. I will then go with whatever sounds best. It is important to do this from where you can clearly hear the bass from the stage, not just the PA sound at the mix position.

Phase adjustment tools can help on a bass guitar if your are combining a microphone and a DI box. Little Labs IBP, Radial’s Phazer and the various plug-in options such as those from Waves will help you to adjust the phase of one signal to help it line up with the other. Even slightly out-of-phase signals will produce comb filtering, which can make the combined sound thin and lacking body. Adjusting the phase can help to minimise any problems and add the punch back into the sound.Large-diaphragm dynamic mics, like the AKG D112 (pictured) are a common choice for use on bass amplifiers.

Compress For Success

There are other tools that can help on bass guitar, compression being the main one. By using a compressor to restrict the dynamic range you can end up with a punchier sound. I like to use a solid-sounding compressor like a Dbx 160 or similar. A slow attack time will let any initial transient information through but will help to control the more troublesome low-end tail of the sound. I normally use a medium delay time, slow enough to compress the note but fast enough so it has recovered before the next note has been played. More dynamic styles of bass playing, such as slap bass, will require a much faster attack time to try and tame those extreme peaks. As with all these things, experimentation and listening play an important role — there are no hard and fast rules. I will also always switch the compressor in and out, in case I am either removing or adding too much level, and also to see if I am actually improving the sound!

Equalisation

Equalisation, as with all things, is a matter of taste, and the bass guitar is no exception. I always try and reference the bass player’s stage sound, and will keeping checking to make sure I haven’t strayed too far. For me there are three main considerations. Can I hear the bass line? Is the bass adding to the overall sound or is it distracting? Is it working well with the drums, particularly the kick?

When combining the signals from a microphone and a DI, a phase-alignment tool such as Radial’s Phazer can help you make sure the two channels sum constructively.The first of these seems obvious but is often the one that is missing in a lot of gigs as it can be the hardest to achieve. Getting clarity whilst maintaining the weight of the bass is a challenge. It is usually to do with clarity in the mid-range, finding the right frequency to boost whilst, possibly, cutting some low mid to help free up some space. At the same time as adding high mids it is important to remember that the bass guitar is usually providing the majority of the low end for most bands, so you have to maintain the weight of the sound, which can be a tricky balancing act at times!

In Context

When soundchecking I always like to get the drummer and bass player to play together so I can hear how the rhythm section are interacting. Musicians always play better when they are playing along to something, and you will find that this will give you a much better idea of what the bass sounds like and also how the drum kit will sound.

The bottom line with bass is to not forget its role in the band, and to work with it in context. A good bass sound will underpin your mix and make it powerful and driving, but it’s important to keep it at the right level, and in balance with the other members of the band. Making sure what you do as an engineer is in context with what is coming off stage is crucial. At all times though, listen and experiment!