BASSIC INSTINCT

Recording Bass Instruments

Published in SOS October 2001
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Technique : Recording/Mixing

Paul White provides some practical tips for achieving better recorded bass guitar and bass synth sounds.

In the context of pop music, bass instruments tend either to be synthesizers or bass guitars, and in both cases choosing an appropriate sound at source is just as important as the recording technique itself. Indeed, in the case of the synthesizer, recording may comprise little more than playing the part into a MIDI sequencer, though, as we shall see later in the article, some post-processing may be necessary in order to get the best results.

Today, bass guitars can be DI'd very successfully, either via a DI box, often followed by a compressor, or by using one of the new breed of modelling preamplifiers that cater for basses, such as the Line 6 Bass Pod or the Johnson J Station. If you're using one of these devices, the recording process can be simplified to choosing an appropria

Using new strings often helps to bring back some of the 'edge and detail' that naturally subsides as the strings begin to wear and stretch.

te sound and setting a suitable record level. Nevertheless, arriving at the right sound isn't always easy, so I'll be talking more on that subject later in the article.

Where a regular DI box is being used, it must have a high-impedance input unless the bass guitar has active pickups, and where a compressor is being used, this should ideally be set to compress fairly lightly to leave some leeway to add more compression if required when mixing. Compression is easy to add but very difficult to remove. I'd recommend you start off with a ratio of around 4:1 with a release time somewhere around a quarter of a second, but if you have a compressor with an

If you set your compressor's attack and, especially, release times too fast, it will actually follow the slow-moving waveform of the bass signal, and not provide any useful compression at all!

auto attack and release setting, you might find that this works more reliably, especially on bass parts where the style changes throughout the song. If you don't have a model with an auto mode, experiment with the attack time to see what produces the best attack sound for the instrument -- it'll probably be between 10 and 50mS. As to gain reduction, aim to trim no more than 8dB off the loudest notes if the bass is being played conventionally, but if there's a lot of dynamics, such as in slap/pull playing, then use your ears to gauge when you have just enough compression to even out the sound. A slower attack time allows the transient response of the bass to be retained.

Some bassists, and apparently Sir Paul McCartney is one of them, prefer to mic an amp rather than use a DI, as miking produces a different sound and one that sometimes sits better with the rest of themix. Others prefer to both mic an amp and DI, then balance the two signals for the best sound. If you try this latter approach, try flipping the phase of either the mic or DI channel to see if one setting gives you a better sound than the other. The chances are that one position will produce more bass than the other due to the effects of partial phase cancellation.

The interesting part of recording bass amplifiers is choosing a suitable mic and finding a good place to put it. Most dynamic vocal mics have a built-in low-frequency roll-off to compensate for the natural bass boost caused by the proximity effect when the mic is used very close to the lips. Therefore you'll most likely find that using your vocal mic will deliver less low-end punch than you want, unless it's jammed right up against the speaker grille, and even then it may not be enough. If you have a vocal mic with a switchable low-cut filter (high-pass filter), then by all means give that a try, with the filter set to its flat position, or choose a general-purpose dynamic mic like the Sennheiser MD421 that has a naturally good bass extension.

Dedicated bass microphones, such as the types used on kick drums, will produce the greatest depth of tone, as these are tuned to emphasise low frequencies. But be aware that many of these have anything but a flat frequency response, so it's a matter of trying them out and seeing if you like the result. The resonant-cavity technique used by these mikes to add weight and power to kick drums might also tend to over-emphasise just one or two notes in the bass line. Because bass amplifiers cause a lot of local vibration, mounting the mic in a shockmount cradle is a wise precaution against stand-borne noise.

It is well worth keeping the bass amp turned down as far as is practicable -- give the bassist headphones if he or she wants to listen loudly. I know it's not the same, and they won't be able to 'feel' the bass, but it makes the rec

Synth players may find that playing bass parts through a miked bass amp will produce a sound that is subjectively more powerful than simply DI'ing, but a halfway house approach that often yields excellent results is to run the synth part through a guitar preamp that includes a speaker simulator. This warms up the sound enormously, while at the same time attenuating higher frequencies that might otherwise conflict with other parts of your mix.

ording a whole lot cleaner. Turning the bass amp down stops it rattling quite as much, and also reduces the LF spill into any other mics in the studio. Controlling LF spill is almost impossible because of the long wavelengths involved -- screens are virtually useless, so control at source is the only option. If the bass amp really has to be loud, consider placing it in a different room altogether.

As an alternative to a dynamic microphone, you can use a capacitor microphone with the bass roll-off switched out, as many of these go down to pipe-organ bass pedal frequencies quite happily. They're a little more sensitive to loud sounds than dynamic mics, but, unless your bass amp is being used at stadium volumes, most capacitor mics will be happy enough, though you may need to switch in a pad, either on the mic or at the mixer end, if the signal is too hot. Once again, capacitor mics produce a different tonality to dynamic models, so if you have access to both types, compare them and see which sound you prefer. Capacitor mics tend to have a more open quality at higher frequencies, and most bass instruments generate high harmonics as well as deep fundamentals, so it can make a difference.

Traditionally, electric guitars are recorded using a dynamic mic jammed up against the speaker cloth and pointing directly down the throat of one of the speakers, but bass sounds seem to need space to breath, so placing the mic between six inches and 18 inches from the grill may sound better. When miking an amp, there are so many variables interacting (room, speaker and mic characteristics) that it's impossible to provide a 'one size fits all' mic placement solution, so start out with the mic around 12 inches from the centre of the best sounding speaker in the cabinet and then make small adjustments while listening to the result. Pushing the mic closer will reduce any contribution from room reflections and from the other speakers and will also increase the bass boost due to proximity effect (cardioid and figure-of-eight patterns only), while moving it away will allow the room to have a greater influence.

Because sound reflects from floors, you may notice some tonal difference depending on whether the speaker is on a solid floor or carpet, and the height of the mic from the floor can also make a difference. If the floor is solid, placing a PZM (pressure zone or boundary mic) on the floor in front of the cabinet can work well. But don't try it on a wooden stage if the rest of the band and drum kit are contributing to floor vibrations! If you're using a cab with multiple speakers, such as a 4x12 or 4x10, see if you can hear a difference between miking one of the lower speakers and miking one of the upper speakers. You can also put the cabinet on a stand if the floor reflections are influencing the sound in an undesirable way.

Ultimately, all that matters is the sound, and most genres of music have specific sound types associated with them. For example, a typical pop bass today is much clearer sounding than it was in the 60s or 70s, but it will still be designed to sit in the background, driving the song along rather than striving for the listener's attention. Miking an amp or using a speaker simulator preamp helps in this respect, as it smooths out the attention-grabbing high end allowing the bass to get on with its job. Alternatively, if anyone has just rediscovered the Stranglers or listened to some of the early Who records, they'll notice that the bass is more predominant and is often characterised by a brighter, more throaty sound, but still with lots of low end. The throaty tone is due to amp distortion, something that's easy to simulate using a modelling preamp or, if you're miking an amp, a distortion pedal, but the secret is not to add too much distortion, as the sound will otherwise lose all its focus.

Interestingly, using the same guitar amp distortion techniques on synth basses can produce some seriously 'attitudinous' tones, and you can often hear good examples of this in TV commercials. If you try this using an overdrive pedal, you'll almost certainly need to use a speaker simulator box, or at the least some fairly aggressive high cut EQ, to stop the sound from being too raspy or edgy.

Another aspect of bass sound that always requires attention is the area of overlap between the bass instrument and other elements of the mix, especially the kick drum. These two sounds occupy similar frequency bands, and where the kick is electronic rather than acoustic, it's quite easy for the sounds to merge into a wall of low-frequency stodge. This is particularly true where the bass notes are long -- it's less of a problem where brighter, fast attack bass sounds are being used in a more percussive way, as is often demons

If you don't have a shockmount for your particular microphone, try placing the stand on a foam-rubber pad or dense sponge to provide some mechanical decoupling.

trated in dance music. One thing that can help is to check out a rough mix on a small home hi-fi or a car system (without a boot full of subwoofer) to see if the bass sound still works. A 25Hz sine-wave bottom note might sound hugely impressive on big studio monitors, but played back on small speakers it will be all but inaudible. For a bass sound to translate well on all systems, there needs to be a useful amount of energy in the 100-200Hz range as well as in the 40-80Hz deep bass range. Plug-ins such as Waves' MaxxBass can be used to salvage already recorded bass tracks that don't have enough low mid-frequency energy as they can synthesize it from the existing low bass, but you can also try adding a little controlled distortion, as that also introduces higher harmonics.

Recording Acoustic Double Bass     To the recording engineer the acoustic double bass represents an entirely different challenge to the electric bass. For a start, the sound is produced by a sizeable chunk of resonant wood, and secondly, it ain't that loud to start with. You can either use a microphone or an acoustic pickup, or both at once. If you're trying the microphone approach, remember that the double bass can generate fundamentals down around the 40Hz mark, so a microphone with an extended low-frequency response is called for. Most engineers like to use large-diaphragm condenser mics -- the Neumann U87 or AKG C414 are very popular in large studios, but more affordable large-diaphragm mics should provide similarly good results. There is nothing to prevent you using a small-diaphragm mic, though, as many have excellent low-frequency responses -- the Sennheiser MKH range, for example. The typical miking position for a single instrument is fairly close (20-30cm) to its front and a little higher than the bridge, looking down at the strings. It is the wooden panels of the front of the instrument which radiate most of the sound, so experimenting with the proximity and angling of the mic can have a significant effect on the sound quality. Moving the mic closer to the f-hole on the high-string side tends to produce a fuller, warmer sound, whereas moving further away and higher up tends to produce a lighter, tighter sound. Moving more around to the sides, or looking up at the front from closer to the floor gives a duller, more weighty sound which would be more typical for adding weight to an orchestral balance. As always, be careful when using close cardioid or other directional mics, as the proximity effect can increase the low bass output substantially. If the acoustic environment permits, a more distant miking position can be very effective and produces a more natural effect. Try placing the mic between one and two metres away, but still aiming it just above the bridge. Beware of any kind of rostrum or staging when working with double bass players. The spike at the base of the instrument couples its vibrations very effectively into the flooring, and if this happens to be a lightweight rostrum, the whole staging can act as a resonator, producing a considerable amount of colouration. Where it is necessary to record the bass played in a live situation, better separation can be obtained by mounting a mic actually in the f-hole, under the foot of the bridge (looking up), or even wedged between the tail-piece and the body (looking up, again). There are specialist mic systems for this situation which won't damage the instrument, including the one designed by Gregg Jackman (who was interviewed in SOS March 2001) or the contact mics available from Accusound, for example. A DIY miking alternative is to use a slim-bodied microphone wrapped in sufficient foam to support it either in the f-hole, or wedged under the bridge or tailpeice. A little electrical insulating tape can be useful to help hold the wrapped package in place, but don't use gaffer tape, as the glue is too strong and will almost certainly damage the intrument's varnish. A lot of bass players have already fitted some kind of pickup to their instruments -- particularly those who play regularly in jazz bands and the like. This is usually some kind of contact mic fitted somewhere near the bridge, and will have been positioned to produce the kind of sound the player likes with his own equipment -- although it may not suit your requirements as well! In general, a good pickup will tend to give a more mechanical sound, usually with greater clarity and definition, but less body and warmth. Conversely, a poor one mounted in a bad position can produce a very heavy, lumbering kind of sound which is very difficult to use within a mix. Watch out for rattles -- the lead from the pickup to the connector and the mounting of the connector itself are notorious for being poorly secured and consequently rattling. If you decide to combine a mic feed with the pickup, check on the phasing of the two sources -- the configuration with the greater bass output is the one to use. Hugh Robjohns

Another thing you learn as you gain experience is that, no matter how the bass sounds when you first set up the recording, it will sound quite different in the context of the complete mix, so you may have to use some fairly heavy-handed EQ to make it sit in properly. Don't be afraid to do this, because, unlike vocals that sound best when

When miking up a bass cab, a good rule of thumb is that moving the microphone off the axis of the speaker usually results in a warmer fuller sound. It's worth experimenting a little with this, as a move of only a few inches can make a significant tonal change here.

messed with as little as possible, bass guitars and bass synths are not natural sounds, and so we have no real built-in expectations of how they ought to sound. If the bass is overlapping another sound with detrimental results, then either shave off some top end or notch out the offending frequency. Similarly, if the bass sound has lots of low end, but you can't get it loud enough in the mix, roll off some of that low end and then you'll be able to turn the whole bass part up.

Where the bass sound is being driven from a MIDI track, you can, of course, change the synth sound itself while you're setting up the mix. If deep editing doesn't take your fancy, consider layering two bass parts to get the effect you need. For example, a bass sound that lacks depth can be layered with a deep sound that uses only a very simple waveform, such as a sine or triangle. This will add a lot of weight to the bottom without changing the basic sound too much. Conversely, an over-simple bass sound can be livened up by layering in a more harmonically rich sound. A useful trick is to use a shorter, perhaps slightly percussive sound for the harmonically rich layer to give the note some definition, while the depth of the simpler sound will underpin the rhythm section without getting in the way.

Finally, compression can be used in the mix to increase the average bass energy, even on some synth sounds, so don't be afraid to try compressing synths, especially if the sounds are made up of layers or have percussive envelopes. More aggressive compression or even limiting may be necessary when using bass synth

In smaller rooms, you may notice the room modes causing some notes to sound more lively or boomy than others, so moving the speaker cab around in the room to find the most even spot is a worthwhile exercise.

sounds that have highly resonant filter sweeps, as these can cause huge energy peaks that need taming if you're to maintain a suitable average level. With virtual instruments, you can easily do this using a plug-in, while, with a hardware module, you'll need to use a hardware compressor. If the module is multitimbral and doesn't have enough outputs to allow you to separate the bass part, you may be better off recording the synth output (bass part only) to an audio track and then compressing it.

As is so often the case, a degree of experimentation is needed to get the best results, but hopefully I've suggested a few areas where your experimentation might be time well spent. Bass sounds are such an integral part of today's music, yet, in so many cases, they're less effective than they would be if a little more care had been applied when recording and mixing.