Bass, How Low Can You Go?
It may be at the bottom of the mix, but it's often the heart of the song: the bass. Tom McLaughlin offers some sound advice on sampling the electric bass guitar.
Listening to commercial sample libraries, you'd be forgiven for believing that the electric bass is capable of producing only a handful of different sounds. A session with your sampler could take your music to new depths.
NEW STRINGS MAKE a difference like night and day, and can give a mediocre instrument a new lease of life, producing a brighter sound than an old, beat-up set. Strings come in several gauges, metal alloy combinations and flat or round outer windings. Flatwound strings keep finger squeaks to a minimum but tend to lose their tone in a matter of weeks. Even when new, flatwounds never seem a match for roundwound strings' crispiness and clarity. New strings don't come cheap though (£15-20 a set). Simply cleaning the grime and finger perspiration from a used set of strings with isopropyl alcohol (from your chemist) or tape-head cleaner, can make a big difference and is the next best thing to buying a new set if your budget doesn't allow it.
How and where you pluck the string has a lot to do with the tone colour of the sound. In addition to your fingers, there are all sorts of plectrums available, made from a wide variety of materials. The nylon variety have the widest range of flexibilities, ranging in hardness from a baby's fingernail to a buffalo tooth. There are also plectrums made from stainless steel, stone and occasionally you'll find them in seashell or hardwood.
It's all a matter of taste but generally hard plectrums give a more immediate response, brighter tone, and more pronounced attack than softies. Metal plectrums add a "zing" to the front edge of notes with the metal-to-metal contact bringing out upper harmonics "other plectrums fail to reach"; this results in a very aggressive and distinctive bass sound.
The force with which a string is plucked not only gives a brighter sound, it causes notes to begin sharp. The greater the force used to set a string into motion, the sharper the initial pitch is likely to be and the longer it will take the string to settle down to its proper pitch.
But where you pluck a string and the effect on its harmonic profile is really a separate issue. Suffice to say here that plucking a string at half its length reduces or cancels every second harmonic. Since only half the harmonics are prominent this is the mellowest and "roundest" plucking position, producing a fruity, square wavelike tone. The further away from its centre you pluck a string the brighter the string will sound, mainly, but not solely, because fewer harmonics are cancelled out. Starting at its centre and working your way to the bridge, listen to the tone colour as you repeatedly pluck a string with varying degrees of forcefulness and a selection of plectrum gauges (not forgetting your fingers) to get an idea as to the wide palette of timbres open to you.
TO AMPLIFY, OR not to amplify, that is the question. Direct injection of the instrument's output, either into your sampler or after passing through effects and/or a mixer, will give you a crisp sound but may emphasise finger noise and string squeaks. Miking up the sound from an amplifier adds the coloration of the amplifier, tone control circuitry, speaker and microphone, and gives a warmer sound with a natural ambience. Many recording engineers and producers prefer combining both techniques and using the presence of DI'ing and the warmth of amp miking to make a composite bass sound.
THE MIC USED to sample an amplified bass plays a large role in the overall sound. Due to its frequency range and percussive quality, a dynamic microphone with a large diaphragm captures the low frequencies of the bass more authentically than your old faithful vocal mic. Most microphones don't have the low frequency response needed. The fundamental of the bass' low E is about 40Hz. Since 95% of sounds you'd want to record have little or no energy present below 80Hz you'll find many mics go down to only 50 or 60Hz.
Traditional kick-drum mics like the AKG12 or Beyer do the job of picking up very low frequencies admirably but seem a bit lacking in the mid-upper frequency range. Hefty equalisation in the 3k to 8kHz range is needed with these mics for a crisp, modern bass sound. Using a second mic, one with a brighter mid range, is often a more desirable alternative.
If a general-purpose mic is all you have you'll need to heavily equalise the bottom end to do the bass justice. It takes work but it can be done, often with little more than the bass and treble/boost cut and mid parametric equalisation on your bog-standard mixer.
A HOST OF companies manufacture combo amplifiers designed to flatter the electric bass. The variety of tone control/amplifier circuitry, speaker sizes/configurations and enclosure designs available is a good example of man's ingenuity. Effectively amplifying low frequencies has several physical limitations to hamper a straightforward design approach. In terms of size needed for an acoustic resonator to project the fundamental of a note, low means B-I-G. In the case of very low (40Hz) means V-E-R-Y big (we could be talking the volume of a small-sized bedroom). The fact that manufacturers have managed to bring us bass amplifiers that we can lift, let alone throw in the boot of a car, is quite an accomplishment.
"Lower sampling rates may mean that a loop is unnecessary, but the downward harmonic movement during notes often makes finding smooth long loops a headache"
When miking up amplifiers, give the speaker room to "breathe" by placing the mic 9-12" from the speaker cone. Pointing the mic directly at the centre of the' speaker will emphasise the mid-upper frequencies but often adds a boomy thud to the attack portion of samples. You may want this. If not, moving the microphone so that it faces the speaker at an angle will prevent its occurrence.
Positioning a single microphone to record a bass amp with multiple speakers is preferable to using several mics. The bass' low register will accentuate any phase inaccuracies between microphones and multiple mics may cause part of your sound to disappear. If you do choose to use more than one mic and find that the sound coming through your monitors bears little resemblance to what you hear in the room, reversing the phase of one or more microphones may be necessary. Comprehensive mixing consoles will have a provision for reversing the phase of a channel; it's a simple and inexpensive circuit to install, otherwise you'll have to make up a lead wired out of phase (swap the wires around at one end) with your other leads, but do remember to mark it.
ALWAYS START WITH the instrument's tone controls before resorting to external means. Set any amp, mixer and effects (if you're using them) to flat and fiddle around with the bass' onboard tone controls to see how close you can get to the sound you're after. Take a sample of it and see how it sounds. You may find it needs very little treatment for a straightforward electric bass sound. If not, it'll give you a good idea what needs to be done. If too little top end is coming back from your sampler, try a higher sampling rate before subjecting the top end to equalisation.
When using a graphic or parametric equaliser, try cutting frequencies around its middle range a little bit - between 250-500Hz. Cutting in this area helps the bass sound a lot less muddy. Boosting frequencies in the 4.5-7kHz range will improve definition, accentuating the pluck or pop portion of the sound (and string squeak), boosting between 40-200Hz will add "balls" by increasing the fundamental and lower harmonics. Be careful with frequencies under 80Hz - a "sub-basement" bottom end may "boom" when transposed upwards. If need be, a response curve more to your liking can be fashioned easily enough when session time comes, with a graphic or parametric equaliser.
IF ONE EFFECT or treatment is most responsible for the modern bass guitar sound it has to be compression. Even though the electric guitar and bass have substantially more sustain than their acoustic counterparts, they're still plucked string instruments and notes are not infinitely sustainable. Compressing a bass won't lengthen its notes (although sample looping will), but what there is of a note will stand more of a chance of being heard. Compression levels out the loudness of input signals, and used to the extreme will eliminate any amplitude variation on the length of a note - the bass will essentially be either on or off. By setting the attack control on your compressor to a few milliseconds, the percussive entry to notes can be exaggerated, giving today's punchy bass sounds.
FULL REVERB TENDS to confuse the bottom end occupied by the bass (there are few things worse in life than a confused bottom end). A little added ambience on DI'd bass will help prevent your samples sounding too little; a wee bit will do the trick. Go easy on the reverb's bottom end. If you can hear it as an effect it's probably too much.
I'm fond of putting a small amount of Yamaha's "Early Reflections" on DI'd bass and guitar. This is an ambience programme on their SPX and REV series of digital reverbs that excels in giving a "live" feel, adding the impression of a sound bouncing off of walls in a room, without the thickness associated with typical room, hall, spring or plate reverbs.
Flanging, phase shifting, chorus, harmoniser, delays, octave dividing and overdrive all work well with electric bass. Although of limited bandwidth, the richness of analogue effects actually seems to complement the range of the bass. The noise usually inherent in analogue effects can easily be filtered out without affecting the bass' tone to any great extent.
Flanging and phase shifting add harmonic movement to sounds by cancelling certain frequency bands and accentuating others. In addition to an internal LFO for modulation, some flangers have an envelope follower circuit that allows the flange to follow the amplitude envelope of the input instrument. This adds an almost vocal quality to the bass. Chorusing adds richness and depth to the bass - anything from the simple chorus with a delay line to the complex chorus algorithms available on digital reverbs and multiple effects units.
Effects are a special case with the bass. To make sure that the fundamental and lower harmonics remain strong, it's wise to carefully balance the treated and untreated bass signals. Some effects units have this provision onboard. Failing that, you'll need to split the bass' output, send one half to the effect and blend them together with a mixer. Fading the effected signal in (with the aid of a noise gate set to a slow attack) ensures a crisp, clean pluck.
AS THE FREQUENCY spectrum of the bass is so low, we can often afford to sample it at lower rates than with other instruments. (The 32nd harmonic of the bass' high E is less than 4Hz.) Valuable memory space may be saved when working at lower sampling rates while still capturing the character of the instrument. Use common sense with sampling rates; you should be able to get away with lower sampling rates for a mellow jazz bass than, say, for a crisp, slap sound. Sampling rates giving a playback response of between 4-12kHz are a good starting point to experiment with.
"The most obvious use for velocity switching is to chop between soft and loud, slapped or popped versions of a note, but don't rule out switching to harmonics or octaves."
It's important that the trigger at the input of your sampler be set low enough not to lose any attack transients on the pluck portion of bass notes. If you have the choice between automatic or manual triggering, you can hit the manual trigger then quickly play your bass, editing off the blank space before the note at a later time. Leaving a small amount of string squeak or finger noise will help give the illusion of a real bass being played.
Lower sampling rates also mean lower samples and may enable you to record bass samples so long that a loop is unnecessary; the continual downward harmonic movement throughout the duration of plucked string notes often makes finding smooth long loops a headache. Alternating loops and loop cross-fading sometimes help, but due to the decrease in amplitude and flattening of pitch, there almost always seems to be some tell-tale cyclic movement that gives the game away. A "short" loop (where the loop is only one, two, four or eight cycles long) may be the best compromise for problem bass samples. If you find the right waveform (s) to loop around midway in the sample, the effect of heavy compression can be achieved.
MAPPING YOUR BASS across the keyboard should be quite straightforward if you sampled a comprehensive set of pitches in the first place. If your bass part is not too demanding you'd be surprised at how few bass samples you can actually get away with.
As with any keyboard map, the best place to start is by assigning samples to notes relating to the original sampled pitches, your ear telling you how far from the original pitch a sample can be taken to meet its neighbouring sample. For those without velocity switching, soft and loud versions of the same bass sound can be assigned to different keyboard zones.
Some samplers allow you to sample two sounds and switch or cross-fade between them once a pre-chosen MIDI velocity is reached. With velocity crossfading, the harder you hit a key, the more dominant the "loud" sample will be. This requires two Digitally Controlled Amplifiers to carry out. Velocity Switching requires only one DCA, switching to the louder sample once the velocity threshold is reached.
The most obvious application of this facility is to chop between soft and loud bass samples. Loud samples may be slapped or popped versions of a bass note, but don't rule out switching to harmonics or octaves. Loud samples needn't be technically perfect; a small amount of string "rattle" or squeak often adds aggression and realism to a loud bass sample.
THERE ARE TWO types of filter commonly available on samplers; fixed cutoff-frequency low-pass filters, and envelope-controllable low-pass filters. Some samplers have both. Occasionally you'll come across a high-pass or bandpass filter but these are more likely to be found in external software packages than resident in a sampler's internal operating software.
The cutoff of fixed-frequency low-pass filters can be adjusted to set the maximum brightness of a sample. In the case of sampled bass this is ideal for minimising unwanted tape hiss or amplifier noise.
Envelope control of a low-pass filter's cutoff must increase a sampler's usefulness by at least ten-fold. Even a simple four-stage ADSR envelope on a Digitally Controlled Filter (DCF) offers so much more scope to the manipulation of samples that a serious "pro" sampler wouldn't be caught dead without one. (Hear that guys?)
As nice as a short loop's tone colour might be, the human ear gets bored listening to sounds with no harmonic movement for even short periods of time. Bass samples with short loops benefit greatly from clever use of a DCF. Try setting the attack and decay controls to zero and, while holding down a note on the keyboard, adjust the sustain of your filter's envelope to let only the first few harmonics of your short loop through - the tone colour you'd expect to hear just before a bass note dies away to nothing. From there it's a simple exercise adjusting the decay control to start the sample off bright and decrease the filter cutoff to the sustain level over, say 5-10 seconds, simulating the natural decay characteristics of plucked strings.
By manipulating the filter envelope and feedback amount, an effect resembling the old faithful funky bass synth can be superimposed on a sampled bass. Fun stuff. More snap can be added to the attack portion of samples with a DCF and by fading in both the DCA and DCF something approaching a bowed string bass can be achieved. Faded-in harmonics border on the ethereal.
Modern instruments and studio techniques allow the tailoring of bass sounds as never before; sampling enables us to store these sounds on floppy disk ready for instant retrieval. So what's your excuse? Get your hands on an electric bass, start sampling and get your bottom end together.
Feature by Tom McLaughlin
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