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Archive-name: music/bass-faq/part2
Version: 2.3 Posting-Frequency: monthly Last-modified: 1996/2/12 See reader questions & answers on this topic! - Help others by sharing your knowledge
REC.MUSIC.MAKERS.BASS
Frequently Asked Questions (FAQ)
Part 2: Answers to Questions 12-21
12. How are 5 and 6 string basses tuned? What are the advantages and
disadvantages of them? How are 8 and 12 string basses tuned and
what are their advantages and disadvantages?
5 and 6 string basses have extra strings either above or below the
normal 4 strings. On 5 string basses, the extra string is either
tuned to B below the low E or to C above the high G. Rock and pop
players tend to find the low B more useful, while jazz players and
chord players tend to find the high C more useful. 6 string basses
usually add both a low B and a high C although a few players add a
high C and a high F above that. In the 60's a few makers (notably
Danelectro and Fender) made basses that had 6 strings and were
meant to be tuned E-A-D-G-B-E, same as a guitar but one octave
lower. This idea never really caught on, and almost no one tunes a
bass this way anymore.
The advantage to the extra strings are that you can reach more
notes in a given position, and can get some notes you could not
otherwise play. The disadvantages are that the neck must be wider
to accomodate the extra strings and that string sets are more
expensive for 5-and-6 string basses.
8 string basses are constructed similarly to 12 string guitars;
the strings come in pairs, each pair containing a string tuned
normally and another string tuned one octave higher. Both strings
are plucked or picked simultaneously Most 12-string basses have
the strings in triplets, one at the normal pitch and two tuned one
octave higher, to get a fuller sound on the top note. There are
also some 12 string basses which have 6 pairs of strings instead
of four triplets. A 10 string bass could be constructed but no one
has ever marketed one. There have even been a few 18 string basses
constructed which had strings in triplets but these were built
more to demonstrate the strength of graphite necks than for actual
use.
The advantage of 8 and 12 string basses is that because several
strings are played simultaneously they have a richer, fuller sound
that a regular bass. The disadvantages are that playing becomes
much more difficult because both strings have to be fingered and
plucked. In addition, strings for 8 and 12 string basses can be
somewhat difficult to buy as very few companies make them and not
many people buy them. Many manufacturers of such basses either
sell strings directly or can tell you who supplies strings for
their basses. If you are willing to order strings by mail this
will usually get you what you need.
13. Can I detune my 4-string to B-E-A-D?
Re-tuning your 4-string to B-E-A-D can be very simple or it can be
impossible. Usually all you have to do is replace the strings and
modify the nut. However, some basses cannot accomodate a B string
on the bridge end. Other than that, there should be no adverse
effects (I have been using BEAD-tuning for two years now).
14. What is the difference between a preamplifier and a power
amplifier?
Bass amplifiers, whether they are combo amps or stage rigs,
contain three components: the preamplifer, power amplifier, and
the speakers. The signal from your bass passes to the speakers in
three stages, with an amplifier between each of the stages. The
signal from your bass is carried at instrument level; floor
pedals, which your bass plugs into directly, operate on the signal
at this level. The instrument level signal is amplified to line
level by the preamp. The line level signal is passed to
rackmounted effects. Because the line level signal is more
powerful than the instrument level one, rackmounts effects add
less noise relative to the level of the signal than floor effects
do, which is why professionals prefer them. Most preamps sold
commercially also include a number of line level effects, though
not all do. After the line level signal is processed it is passed
to one or more power amplifiers. Most rigs use only one power amp
but if you are biamping you would use two. The line level signal
can also be sent to the PA system if your band uses one. The power
amp amplifies the signal to the the much higher levels that are
used to drive the speakers. The power power rating of a guitar or
bass amp refers to the total wattage that is sent to the speakers
by the power amplifier stage of the amp.
You can buy a combination ample that contains a preamp, a power
amp, and a speaker all in one box, or you can buy a separate
preamp, power amp, and speaker cabinet. Professionals do the
latter -- it's more expensive, and usually sounds better. It also
gives you more flexibility to mix and match your components to a
particular need. Many combination amps have a preamp-out jack,
which allows you want to send the preamp stage's output somewhere
other than the power amp. There are several reasons for doing
that:
+ You could send the preamp out into a mixing board in addition
to your power amp for sound reinforcement.
+ You could send the preamp out into a tape recorder and record
it.
+ You could send the preamp out into a bunch of effects, and
then connect the effects' output back into "power amp in,"
thus putting the effects in between the preamp and the power
amp stages.
Some combination amps, though not all, also have a power amplifier
in jack which allows you to send a signal from a separate preamp
to the power amplifier directly. Most combination amps also have a
power-amp out jack which allows you to send the power signal to an
external speaker, either in tandem with the internal speaker or
instead of it. Combination amps that have all three features are
almost as flexible as separate stage rigs.
15. What is biamping, and how is it done?
Biamping refers to using separate power amplifiers to amplify
different frequency ranges. (See question 10 for a discussion of
power amplifiers.) In particular, it allows you to use one power
amplifier to amplify your high freqencies and another to amplify
your low frequencies. In most bass amplifier rigs, the preamp
signal is sent to one power amp and the output from that amplifier
is sent to the speaker cabinets, where it may be divided among the
various speakers by a crossover in the cabinet; high signals to
small speakers and horns, low signals to larger speakers. (A
crossover is a filter which separates a signal into high-frequency
and low-frequency components: it may have a knob which allows the
bassist to control the dividing point.)
With biamping, instead of splitting the power amplifier's signal,
you split the preamplifier's signal and send each half to
different power amplifiers. Then, each power amplifier drives its
own speaker load; again, usually small speakers or horns for the
high frequencies and large speakers for the lows. Also, the
crossover used in biamping is usually active (ie it requires a
power supply) whereas those found in speaker cabinets are usually
passive.
Biamping has several advantages:
+ active crossovers don't have inductors, so they exhibit less
intermodulation distortion;
+ active crossovers don't drain the power of the signal to
operate ;
+ the full power range of each amp is available regardless of
the, power requirements of other ranges.
For more information on the engineering side of biamping, an
excellent book is Martin Colloms, "High Performance Loudspeakers",
3rd. edition, pages 188-191 on biamping.
The last item is important because it takes more power to
reproduce low-frequency sounds than high ones. A typical biamp
setup might be to send to highs to a 4x10 cabinet and the lows to
a 1x15, 1x18, or other large subwoofer. If you send your high end
through the subwoofer, your tone will probably suffer and become
muddy, whereas if you send your lows through the 10s they will not
provide as much thump as the subwoofer will. By biamping, you can
send the lows through the subwoofer and still get clarity and tone
from the 10s without forcing the 10s to spend most of their energy
driving very low frequencies.
To get a good sound from biamping requires some fairly close
matching between the crossover, the amplifiers, and the cabinets
used. Done poorly, biamping can sound worse than using a single
amplifier and cabinet. If you biamp, it is better to get a system
designed explicitly for biamping than to assemble components one
by one.
16. How do I adjust the setup on my bass (action, intonation, etc?)
There is an excellent article in issue #153 of the Bottom Line. It
is long but very good. It can be obtained from the Bottom Line
archives by anonymous FTP; the address is ftp.uwp.edu and the back
Bottom Line issues are in the /pub/bass directory.
17. What is the difference between the various types of strings?
There are basically three factors that affect string sound and
playability. The first is whether the strings are flatwound or
roundwound, the second is the gauge of the strings, and the third
is the metal the strings are made from.
Almost all bass strings are made of a central string which is
wrapped in a second layer to make the string thicker. The central
string is called the core of the string. These are usually round,
although some hexagonal core strings exist. The wrapping comes in
two kinds; some strings are wrapped with flat ribbon and some are
wrapped with a round piece of wire. The first kind, called
flatwounds, have a dark sound and are fairly smooth, which makes
them easy on the fingers and the fretboard. The second kind,
called roundwounds, have a much brighter sound, but tend to wear
down your frets or fretboard and chew up your fingers.
Most people prefer roundwound strings for their brighter sound.
Flatwounds are mostly used for fretless basses, for which the
damage caused by round- wounds is especially problematic. There
are also two kinds of compromise strings, called groundrounds and
half-flatwounds. Both of these kinds of strings are flat on one
side and round on the other: this can be achieved by taking a
roundwound string and grinding it flat, by applying pressure to
the string to flatten it, or by wrapping with wire which is
alternately round and flat, so that one side of the string is flat
and the other is round. These types of strings are not easy to
find but some players do use them.
The second question is the gauge of the string. The gauge is
measured by the thickness of the string in inches. A typical set
of light gauge strings might have thicknesses of about 0.040,
0.060, 0.075, 0.090 for the G, D, A, and E strings. A medium gauge
might be about 0.050, 0.070, 0.085, 0.105. Heavy gauge strings are
extremely difficult to find now, for some obscure reason. Most
companies make three gauges of strings: light, medium-light, and
medium. Some companies will sell you individual strings, which
lets you mix and match your strings to get a unique combination of
gauges, but not too many people do this.
Lighter gauge strings tend to have a brighter but thinner sound.
Heavier strings have a more solid sound to them. A major advantage
to light gauge strings is that they require less tension to
produce a given pitch, so that they require less force to fret,
pluck, and bend, whereas heavier gauge strings call for a little
more finger strength.
The third factor is the metal used to make the strings. Almost all
strings are made of either stainless steel or nickel. Stainless
steel has a brighter sound at the expense of being a little harder
on the fingers. The difference is not very great, however. You can
also get strings which are plated with chrome or gold, or various
black metals. These are more for effect than because the plating
does anything to the tone.
Acoustic strings can also be made of nylon or gut as well as
metal. Gut strings are quite expensive but sound very nice. You
can also get strings made of silicon and other exotic materials
for unusual basses, but non-metal strings will not work with
magentic pickups so most people don't use them.
There are a few other factors to consider when buying strings.
Many strings come with a silk wrap around the end of the string
which helps to keep the wrapping on the string from coming
unwound. Cheaper strings don't have this winding. However, if the
string is made with a hex core (as opposed to a round core) then
the wrapping is much less likely to come unwound (it grips a hex
core better) and in that case, the silk wrapping is not as
important. Another important thing to remember is that the strings
have to go on your bass! Most basses require single-ball strings,
with the ball end going at the bridge and the non-ball end being
wrapped around the tuning peg. However, Steinburgers and most
other headless basses require double-ball strings, one ball going
behind the nut and the other behind the bridge. And, to keep
things confusing, some headless basses, notably Kubickis, use
single-ball strings by putting the ball end at the end of the next
andtaking the non-ball end onto a post on the body of the bass.
You cannot use single-ball strings on a double-ball bass and
vice-versa, so make sure you know what you need before you buy.
You also need to buy strings of the appropriate scale. The scale
length of a bass is the distance from the bridge to the nut, ie
the length over which the string vibrates. Most basses are "long
scale" or 34-inch scale length. A few basses, notably old Gibsons,
are "short-scale" or 30-inch scale length. Modulus Graphite basses
are all built to a 35-inch scale length, as are a few other
basses. There is also a "medium-scale" or 32-inch scale length,
and some acoustic bass guitars are built to this scale. When you
buy strings, they need to be the same length as the bass they're
going on, so make sure you know the scale of your bass, and buy
the appropriate strings for it.
Also worth noting is the fact that there are only three major
American manufacturers of strings, and a few more European ones.
Although there are many brands of strings, a lot of those brands
buy their strings from one of the main manufacturers and repackage
them under their own name. Thus, there is less variety in strings
than the number of brands available might suggest. Obviously the
advertising does't affect the sound, so shop intelligently when
you go looking for strings.
18. How does a bass pickup work? What is the difference between the
various kinds of pickups?
A bass pickup works by detecting the changes made by the moving
string in the magnetic field of the pickup. A normal bass pickup
consists of one or more magnets wrapped in coils of thin wire. The
vibration of the metal strings changes the magnetic field of the
pickup, and the changing magnetic field produces a voltage across
the two ends of the wire wrap. This voltage can be detected and
amplified by a bass amp, and then converted back to sound by a
speaker.
This signal needs to be amplified in order to be audible. Passive
pickups do not amplify the signal at all: they require the bass
amp to do all of the amplification. Active pickups contain a small
amplifier inside the pickup housing. This amp boosts the pickups
signal to a higher level which is then sent down the instrument
cable into the amplifier. (Good amplifiers have two input jacks,
one for active basses and one for passive basses, to reflect this
difference.) You can also get basses which have onboard preamps
which take the pickup signal and pass into into an amplifier which
is on the bass but not part of the pickup. These onboard preamps
can also contain tone controls and other electronics; a few
expensive active pickups also contain tone controls inside the
pickup housing.
You can make the pickup stronger or "hotter" by doing any of three
things: using a stronger magnet, wrapping it in more windings of
wire, or raising it closer to the strings. Using a stronger magnet
causes the magnetic field to be stronger, raising the pickup puts
it into a stronger area of the magnetic field, and using more
wrappings of wire causes the moving string to induce a greater
voltage difference within a given magnetic field. Any of these
lets the string create a larger voltage differential across the
pickup, resulting in a louder signal. However, they can also have
an effect on the tone of the bass which you may or may not like.
Also, if you set the pickup too high the string can actually hit
the pickup casing when slapped or plucked hard, and this is
usually not good. There is no optimal height for the pickups: you
can put them anywhere you like as long as you are getting
sufficient signal strength and you're happy with the tone of the
bass. You can also balance your pickups by setting them at
different distances from the different strings, which is useful if
one string tends to be louder or quieter than the others. Most
basses have bridges which let you adjust the string height, but
this affects the action of the string as well as the distance from
string to pickup. Some pickups allow you to adjust the height of
the individual magnets so that you can set the strings at
different distances from the magnets while keeping the action the
same on all strings.
Pickups come in two kinds: single-coil and double coil.
Double-coil pickups pass the signal through two sets of magnets
and wire coils (hence the name) whereas single-coil pickups use a
single set of magnets. The advantage of most double-coil pickups
is that the coils are wired backwards, and the magnets are out of
phase with one another. Since the magnets are inverted in the two
coils, they pick up the string signal out of phase, but they pick
up any noise and hum in phase. Because the coils are wired
backwards, the signal from one of the coils is effectively
inverted before the two signals are added back together: this puts
the string signals back into phase but effectively cancels out any
noise that the pickup received. These pickups are sometimes known
as "humbuckers" for this reason. Not all double-coil pickups are
humbuckers, however: you only get the hum cancelling effect if the
two coils are out of phase _and_ the magnets are out of phase. In
some double-coil pickups the two coils are in phase, not out of
phase, so these pickups do not cancel hum in the way that
humbuckers do.
Another side effect of having two coils in one pickup is that the
two coils do not pick up exactly the same signal from the string,
since they are not located in exactly the same place on the bass.
As a result, when the signals are added back together, some of the
high frequencies of the signal are cancelled out along with the
noise and hum. This gives the pickup a particular sound associated
with humbucking pickups that some people find unattractive, but
others find desirable.
Some double-coil pickups do not place each coil under all four of
the strings. These pickups are sometimes called "split coil" and
the most common configuration is to have one coil under the E and
A strings and the other under the D and G strings. The pickup on a
Precision bass is of this type. This pickup design doesn't cancel
hum quite as effectively as a regular double-coil, since the coils
are farther apart, but it also doesn't cause cancellation of the
high frequncies of the string signal since the signal from each
string is only picked up by one coil, not both.
Single coil pickups, split coil pickups, and humbuckers all have
somewhat different characteristic sounds, though, so all three
kinds of pickups are fairly widely used regardless of their noise
levels. A bass with two single coil pickups or in-phase
double-coil pickups can also cancel hum if the if the two pickups
are of opposite phase and are set at equal volume: in this case
each single-coil pickup acts exactly like one coil of a double-
coil pickup. Since the pickups are farther apart than the two
coils of a single pickup would be, the high frequency cancellation
is somewhat different, less pronounced but affected more
frequencies.Most Fender Jazz basses are built with two single coil
pickups that are out of phase and can therefore be used to cancel
hum this way. Some basses have "phase switches" which let you
change the phase of a pickup's wiring, so that you can get the
"out of phase" sound with the hum cancellation, or you can get the
in phase sound but also get some noise, as you choose.
Some double-coil pickups also have a switch called a "pickup tap";
this lets you pass the signal through only one of the two coils,
thus converting a double-coil pickup to a single-coil. And some
pickups, both single and double coil, have a switch called a "coil
tap" which takes the signal out of the pickup after passing
through only some (usually about half) of the wire wrap. Since the
sound of the pickup is affected by the number of turns of wire in
each coil, having a coil tap lets you get two different sounds
from one pickup.
Some expensive basses also have non-magnetic pickups call piezo
pickups or piezoelectric pickups. These do not contain magnets:
instead, they work by having a small crystal in the bridge of the
bass. When the string vibrates against the crystal, this vibration
produces an electric signal through the crystal, which is sent out
to the amplifier. Basses that use non-metal strings are built with
piezo pickups, and some basses use piezo pickups in addition to
magnetic pickups in order to get more variation in tone. However,
piezo pickups have a much much higher impedance than magnetic
pickups do, and piezo pickups require special onboard preamps or
other amplification tricks in order to sound good.
19. How do I record my bass to tape?
This is a fairly difficult thing to do because most recording
equipment is designed to work best with frequencies higher than
those delivered by bass. However, with the right equipment it is
not hard to achieve a nearly professional quality recording of
your playing.
The simplest thing to do is to get a tape recorder with a
microphone input and plug your bass into it directly, or send it
your preamp signal. This will only allow you to record on one
track, but it's very easy to do and most people have the necessary
equipment at hand. You can also record using a microphone placed
in front of your amplifier, but you will tend to introduce
extraneous noise and unless you are in a recording studio you are
better off using a direct input.
If you want to record multiple instruments, or multiple tracks of
a single instrument, you will need to obtain access to a
multi-track recorder. You can buy four-track recorders at most
large music stores, and professional studios have 16, 24, or 32
track recorders.
Once you have access to a recorder, the main decision you have to
make is whether to send your bass signal to the recorder directly,
to pass the signal through a preamp, or to send the signal to
speakers and use a microphone to record the sounds from the
speakers.
If you go direct, you will need to convert your signal into a form
that the recorder can take as an input. This can be done using a
tool called a direct box, which most studios have, which will
convert it to a balanced, low-impedance signal of the form that
most recorders expect, but leave it otherwise unaffected. Or, you
can use your own preamp to raise the signal to line level plus
doing whatever effects processing you like. Your preamp may have a
balanced output, or if not, you can run the line level signal into
most direct boxes as well. However, if you are in a studio the
engineer may have access to line-level effects like equalization
and reverb which are better than those found in floor effects or
preamps. If you can get the engineer's attention for 15 or 20
minutes consider using the studio's quipment instead as you can
get better performance from studio equipment in many cases. The
drawback to so doing is that it takes time, plus you have to
explain to the engineer how you want the sound to be whereas your
preamp is under your own control.
Another common problem is providing a constant signal from the
bass. In particular, if you do a lot of slapping and popping, or
you like to play chords on your bass, you might have a hard time
recording a clean track without a compressor. A compressor will
quiet down the louder notes you play and boost the quiet ones to
produce a constant volume in the recording. If you don't have
access to a compressor, you can try to simulate this by adjusting
the recording volume as you play the track (or having a friend do
it) You can also increase the volume of a bass solo the same way:
turn the recording volume up for the solo, then turn it back down
when the solo is over.
You might also want to use noise reduction to eliminate signal
noise, either from your bass and amplifier, or from a compressor
if you use one. If your recorder has dbx then you don't have to be
so critical of the signal level because dbx noise reduction gives
you about 90db of dynamic headroom and almost no tape hiss.
You will find that some of the notes you play on the instrument
are louder than others. This is called the "sweet spot". Most
instruments have them, though graphite necks can reduce or
eliminate them. Your recorder should have a VU needle or other
indicator that will tell you how much volume is being recorded.
Adjust your level so that the VU needle does not spend too much
time in the red zone of the indicator: this is an indication that
you are playing loudly enough to damage the recorder.
20. What are some popular effects for bass and what do they do? Is
there a difference between guitar effects and bass effects? In
what order should I plug them together?
There are five main effects for bass, plus some others that aren't
as widely used. They are: compression, distortion, delay, reverb,
and chorus/flange. Most of these effects come in both analog
versions and digital versions. Analog effects act upon the
incoming signal directly, modifying it to produce the output.
Digital effects convert the incoming signal to a pattern of zeroes
and ones (hence the name digital). The resulting code is processed
and the new code is converted back to a signal. Digital effects
are typically cleaner and have fewer side effects than analog ones
do. They are also considerably more flexible as patterns of
numbers are easier to manipulate than electric signals are.
However, analog effects are usually cheaper, and to exactly
replicate the sound of players from the 70's and earlier who used
analog electronics, you have to use analog effects yourself.
(Digital effects weren't in common use until the late 70's, and
weren't commercially available until the early 80's.) However,
either one is fine for use with bass. They will sound a little
different, so try both kinds and choose the one you prefer.
Effects come in two kinds, those designed to work with instrument
level signals and those designed to work with line level signals.
Floor boxes are almost always designed for instrument level, and
rackmount effects for line level. However, check and make sure you
know which you have. It is possible to damage your effects,
especially floor effects, by running the wrong level signal
through them.
There isn't all that much difference between guitar effects and
bass effects and you won't damage anything by running a guitar
through a bass effect or vice versa. However, bass effects are
designed to work better on lower frequencies than guitar effects
are, so you will usually get a better sound by using an effect
designed specifically for bass.
Most effects devices have several names. Where there aren't too
many the following paragraphs try to give them all, along with the
reasons for using one rather than another. However, if you are in
doubt, ask the salesman what an effect does and you should usually
be able to recognize it as one of those described below.
Compression is an effect that keeps the signal strength of your
instrument constant. It can work in one of two ways: it can reduce
loud signals, or it can amplify quiet ones. Compressors usually
have both functions; effects that only quiet loud signals are
called limiters and effects that only amplify quiet ones are
called sustainers. Compression has two purposes. First, it keeps
your volume level constant. This is used in recordings where
constant volume is desirable, and it protects amplifiers and
speakers from having an excessively high signal sent to them that
could burn them out. (Most amplifiers have limiters built in,
which is why they don't get louder beyond a certain point when you
increase the volume control.) Second, they increase the sustain of
your instrument; as the string vibration begins to die down,
making the signal quieter, the compressor raises the quiet signal,
making it sound as it the string is continuing to vibrate. The
drawback to compressors is that they eliminate sharp changes in
the level of your sounds. This tends to destroy slapping, popping,
and other percussive sounds, and it also alters the individuality
of your sound by changing the attack and the muting of your
fingers.
Most compressors have three knobs: one which controls how quickly
the compressor will react to changes in the incoming signal
(usually labeled attack), one controlling how much the compressor
will boost the signal (sustain or compression) and one controlling
the level the compressor will try to attain (level). Manufacturers
tend to adopt their own methods of labeling knobs on effects
boxes; your mileage may vary.
Distortion causes your sound to become more "crunchy" or "grungy".
What it does is to clip the high peaks off your signal, which
makes the wave more like a square wave (which has the
characteristic buzzing sound of distortion) and emphasizes the
higher frequency harmonics of the signal. In the old days,
distortion came from driving an amplifier close to its limit, thus
trimming off the high peaks naturally, and you can still obtain
distortion this way. Tube amplifiers clip more gradually and more
gently than transistor amps do: this causes the resultant
distortion to sound different. Most people prefer tube distortion
to transistor distortion, though not all do. You can drive either
the pre-amp or the power-amp to its limit with most amps: you will
usually get better distortion by overloading the power amplifier,
but try it both ways and see what you get. Be careful not to blow
out your amplifier this way, however; turn it up high enough to
get distortion but no higher. If your amp has a limiter, you may
not be able to do this at all. (Players also used to get
distortion by playing with speakers which had rips in the cones.
It is not recommended that you try this.)
Distortion pedals clip your signal in a more artificial way but
produce a similar tone. They usually have three knobs, one which
controls the mix between noise and instrument signal, one which
controls the tone of the distorted signal, and one which controls
the output level. (Names of knobs varies too widely to permit
suggestions.)
Delay effects take the incoming signal and send it out repeatedly,
with intervals ranging from microseconds to 30 seconds or more.
They can be used to add fullness to your sound, to produce doubled
parts without having to hit each note twice, or, with long delays,
enable you to accompany yourself by playing a 30-second part
through a 30-second delay and then playing a second part over it!
Delay boxes usually have three knobs: one controls the time
between repeats (delay), one controlling the falloff in volume
between repeats (level), and one controlling the number of repeats
given (repeats).
Reverb effects are similar to delay effects, but mix in a very
large number of very quick, quiet repeats. They simulate the
effect of playing in a small room, where the sounds from the
instrument reflects off the walls, creating a large number of
rapid echoes. They usually have the same three controls as a delay
box, which work about the same way in principle but will have
quite different effects on the sounds.
Chorus and flange effects both simulate the sound of having
multiple instruments playing at once. Consider two basses playing
the same part. They will not be perfectly together; they will be
very slightly out of tune and the players will hit the notes at
slightly different times. A chorus pedal simulates this effect by
taking an input signal and duplicating it, with the duplicate
signal slightly delayed and slightly out of phase with the
original. In addition, the amount of delay and phase shift varies
over time. This is designed to simulate the second player being
slightly off from the first one.
The difference betwwen chorus and flange is one of degree only;
chorus pedals use small delays and phase shifts to produce a very
subtle effect. Flangers use even smaller delays but vary the
length of the delay and the phase changes to produce a more
noticeable effect. If you turn on a flanger and don't play
anything, you will hear a characteristic "whoosh" sound which is
the result of certain frequencies being cancelled in the two
signals before being sent to the amplifier.
Choruses and flangers usually have three knobs; one to control the
extent of shift produced by the effect (depth), one to control the
rate at which the shift changes (speed) and one to control how
much of the second signal is mixed together with the first (level
or intensity). Cheap choruses will omit the latter knob. Some
choruses will have a fourth knob which controls the overall signal
from the effect as well.
Many effects boxes, most commonly choruses and delays, contain a
stero split which allows you to send the original or "dry" signal
to one amplifier and the affected or "wet" signal to another. This
is commonly used to send the dry signal to the PA and the wet
signal to the stage amplifier, or vice-versa. Or it can be used to
power two different stage amplifiers to get a stereo sound, though
this involves lugging twice as much equipment around.
Most players use the following sequence for their effects:
compression first, then distortion, then chorus/flange, then
delay, and last reverb. However, there is nothing magical about
this ordering, and you should feel free to experiment with
alternate orderings to get different sounds.
For more information on effects, consult the excellent book
"Getting Great Guitar Sounds" by Michael Ross, which discusses the
acoustic properties of electric instruments and the workings of
amplifiers as well as effects.
21. What is the difference between digital and analog electronics?
There are quite a number of differences between digital and analog
electronics, which make analog better for some applications and
digital better for others.
First, a little information on bass signals. When you pluck the
string on your bass, it vibrates back and forth. The vibration of
the string causes sounds waves to be transmitted through the air
at the same pitch as the string, and that's what your ears detect
as sound. The idea of amplication is to get an electronic
representation of the string's vibration, and then make the amp's
speaker vibrate in exactly the same pattern, thus creating the
same sound as the string (only much louder :)
The job of the pickup is to "read" the position of the string at
any moment in time, and translate that into a voltage. When the
string is not moving, the voltage is zero and there's no sound.
The faster the string is moving, the higher the voltage is, and
moving in one direction induces a positive voltage and the other
direction, negative. Thus, as the string goes back and forth and
back and forth, the voltage in the pickup goes positive and
negative and positive and negative. This voltage signal exactly
replicates the movement of the string, so we now have an
electronic "picture" of the string's movement which we can send on
to the amplifier and speaker.
En route, we are going to want to process this signal. At the very
least we want to amplify it, ie, make it louder. We may also want
to apply equalization or compression, or even a delay or chorus
effect. There are two ways to do these sorts of things; analog,
and digital. Analog techniques use physical electronic effects to
convert the signal, using magentic fields, capacitors, and so
forth. Digital effects use computer circuitry to create a
mathematical representation of the signal, and then manipulate
that signal mathematically. They then convert the processed signal
back to a physical representation to send to the speaker.
Converting the physical representation (ie, the pattern of the
voltages from the bass) into a mathematical representation (a
series of numbers stored in the computer circuit) is called
digitization. Our earlier pattern of voltages going positive,
negative, positive, negative gets translated into a series of
numbers, something like 1, 0.6, 0, -0.6, -1, -0.6, 1, 0.6, 0,
-0.6, -1, -0.6. Since those numbers are now stored inside the
computer circuit, you can do anything you like with them before
you send them over to the speaker to be converted back into sound.
For an amplifier, the analog method of amplification involves
either a vacuum tube or a transistor. Without going into the
details of the physics, what happens is that the amplifier runs
two signals through the vacuum tube/transistor. One is the
incoming signal from the bass, and the other one is the outgoing
signal to the speaker, which is much more powerful. The job of the
tube or transistor is to exactly copy the voltage of the bass
signal onto the speaker signal, which is then sent to the speaker
where the physical signal is converted back to sound.
In a digital amplifier, the electronic signal from the bass is
digitized, but there isn't any manipulation of the digital signal.
It's just sent over to the speaker circuit and sent out there
unaltered, except with more power.
The real power of digitization is that you can do anything you
want with those numbers. Wanna send the signal out backwards? No
problem, just reverse the sequence of the numbers. Effects like
delay, reverb, chorus, and flange are very awkward to create using
magnetic fields and circuits, but very easy to produce using a
computer with a memory bank. That's why most of the uses of
digital technology have been in effects boxes or processing
equipment like MIDI, rather than amplifiers or basses. However, if
you have a digital amplifier already, then it's real easy to build
in a digital EQ or reverb while you're there. You've already
digitized the signal, so you may as well play with it. There is
even one company that makes a digital pickup now; it uses a laser
to detect the position of the string and converts that directly to
a digital signal onboard the bass.
Why use digital electronics? Three main reasons. First, they're
very powerful; numbers in a computer are a lot easier to
manipulate than voltages in circuits. Second, they're much less
subject to noise and interference than analog electronics, because
they're not relying on magnetic fields and other physical effects
that can be disturbed by grounding problems, radio interference,
or other Bad Things in the area. They're also not subject to
signal degradation inside the circuit, as analog electronics are.
This is the same reason that CDs are so much better than analog
cassetes. Third, they're much easier to miniaturize than analog
electronics are. Analog reverbs are huge. Digital reverbs can be
easily packed into a stomp box.
What are the drawbacks of digital electronics? They're expensive.
Essentially, any digital effect box or amplifier has a small
computer built into it to do the mathematical processing. However,
as the cost of computer technology continues to drop, so will the
prices of digital effects, pickups, and amplifiers. So there will
be a lot more digital equipment coming down the pipe in the next 5
or 10 years. Probably not so much in pickups - it is likely that
people are going to stick with analog pickups because the way they
color the sound of the bass can't be easily digitized - but there
will soon be all-digital preamps with digital effects built in,
and that sort of things. And it will all work its way into the
combo amps in time as well.
22. What do the ratings of amplifiers and speakers mean? What is a
watt, or an ohm? What factors must I consider in connecting
amplifiers to speakers?
Any electronic circuit has 3 properties of importance: voltage,
current, and resistance. (Plus some more based on these three). As
you may know, electric current consists of electrons moving along
the wires. Voltage is the amount of energy carried by each
electron. Current is the number moving passed in each second. The
total power of the circuit is given by:
Power = voltage * current
thus, increasing either the voltage or the current will increase
the power of your amplifier.
Resistance is the tendency of a circuit to resist the flow of
electrons (hence the name). The formula for resistance is:
Resistance = voltage/current, or, current = voltage/resistance
Thus, for a given voltage, a circuit of high resistance gives low
current, and a circuit with low resistance gives high current.
Voltage is measured in volts: you get 110 volts out of the wall
(220 if you're in Europe). This is usually transformed by the
amplifier to some other voltage, and there's not much you can do
to change it. However, you can alter the resistance of the circuit
by changing the resistance of the speakers. Changing the
resistance will change the current flow, and therefore the power
of the circuit. Resistance is measured in ohms: typical speakers
and cabinets have 16, 8, or 4 ohms resistance. The current of a
circuit can be deduced from these. Power is measured in watts:
most amplifiers have the maximum amount of power they can deliver
in the name somewhere (ie a Crate B-20 can deliver 20 watts of
power). How loud you are depends on how many watts of power your
are delivering.
Substituting the second equation above into the first one yields:
Power = (voltage^2) / resistance
which gives the relationship between resistance and power
delivered, assuming the amplifier's voltage is held constant. In
fact, the delivered power of an amplifier may be less than this if
the amplifier is not properly matched to the load it is driving.
Most amplifiers are designed to drive a 4 ohm load of speakers. If
you use speakers of more or less resistance than the designed
load, you will not get as much power as you would get driving the
designed load, and if you supply your amplifier with too little
resistance, you may blow it up. It is always best to supply your
amp with speakers of exactly the resistance it was designed to
drive.
Say you have a 55-watt amplifier driving a 4 ohm speaker (which
might be typical). If you replaced the 4 ohm speaker with an 8 ohm
speaker, you would double the resistance of the circuit, which
would halve the current flow. Since power=voltage*current, this
would cut the power in half; thus, your 55 watt amp would only be
delivering 27.5 watts. This is not so efficient (nor so loud),
which is why you would have the 4 ohm speaker in the first
place... Conversely, if you put in a 2 ohm speaker you would
double the current, and double the power to 110 watts, if the amp
was designed to handle a 2 ohm load. Most amps aren't, meaning
that in practice you would probably get much less that 110 watts.
To make matters worse, the power ratings can be measured with
different measurements. The two most typical are peak power and
RMS power. The difference between these two is that RMS (root mean
square) power is calculated by measuring the area under the
alternating power graph (in effect converting it into DC power)
whereas peak power is just that - the peak of the graph. You can
convert figures by multiplying (RMS -> Peak) or dividing (Peak ->
RMS) by 1.41 (square root of 2). Peak power figures sound more
impressive (240VAC is really 340 volts peak) and some
manufacturers use them, but RMS power is more "accurate".
Why wouldn't you want to have as low a resistance as possible? The
answer is that this would increase the power of the circuit (by
increasing the current) and electric components can take only so
much power before they blow up. Amplifiers and speakers are both
rated by the maximum amount of power they can take without going
crispy. Thus, if you have an amp which delivers 100 watts into 4
ohms, and you attach a 2 ohm speaker to it which is rated for 120
watts, you will now have a circuit carrying 200 watts of power
whose components can only handle 100 (amp) and 120 (speaker).
Something will fry in short order. Thus, you want to make sure the
resistance of your speaker load is high enough that your amp can
take the total power of the circuit, and each speaker can handle
its share of the load.
Another reason for not going as low as possible impedance-wise is
that the actual formula for maximum power transfer is:
TotalPower = (Voltage**2)/(SpeakRes+AmpRes)
Solving for speaker power, we get
SpekerPower = (Voltage**2)SpeakRes / (SpeakRes+AmpRes)**2
Assuming that the AmpRes (amp output resistance) is constant and
solving for maximum SpeakerPower results in SpekRes = AmpRes. With
transistor amplifiers the amp output resistance is usually
neglible (ie. << 1 ohm) but most tube amps have output resistances
of 2 - 16 ohms. This means that you must match the impedance of
the speaker with the output impedance of the amplifier.
If you have only one speaker, that speaker is carrying the entire
power of the circuit. However, if you have more than one speaker
(and they are wired in parallel, which they should be) the load is
divided between them. If both speakers have the same resistance
(ie, it is equally hard to push power through them) then each will
take half the power, and the total resistance will be half the
resistance of either speaker. (If you have N identical speakers
with R ohms, the total resistance is R/N.) So, if you have an
amplifier which delivers 50 watts through 8 ohms (meaning that it
delivers 100 watts through 4 ohms, or 25 through 16 ohms) and you
hooked it up to two 8 ohm drivers, the total resistance would now
be half of 8 ohms, or 4 ohms, and the amp would put out 100 watts,
with 50 going to each speaker.
If the speakers do not have the same resistance, then more of the
power will be pushed through the low-resistance speaker. The
formula for the total resistance of two speakers with resistance
R1 and R2 (again, assuming they are wired in parallel) is:
R = 1 / [ (1/R1) + (1/R2) ]
So, if you are hooking a 4 ohm speaker and an 8 ohm speaker
together in a cabinet, the total resistance will be 1 / [ 1/4 +
1/8 ] = 1 / [3/8] = 8/3 ~= 2.67 ohms. Thus, an amp rated for 100
watts through 4 ohms would put out 150 watts under this speaker
load. The power is divided among the speakers in proportion to the
resistance: in this circuit the 4 ohm speaker would get 100 watts
and the 8 ohm speaker would get 50 watts. If you hook together two
8 ohm speakers the resistance is 1 / (1/8+1/8) = 4, as said above.
--
* "Let's see if we can spot any colorful exotic natives in colorful *
* exotic costumes singing colorful exotic songs with their colorful *
* exotic hands out for bakshoesh." - Zebadiah Carter *
* PGP public key available - try finger killer@niksula.cs.hut.fi *
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