The bass range of frequencies and the "bass instruments" of kick drum
and bass guitar give the mixing engineer the most mixing challenges. This range
is very important to many productions but hard to obtain clarity in mixdown. It
is equally hard to judge how much of this range that you have in the mastering process.
How do we get a clear yet powerful low-end in the mix and on our final master? In
this article we will find that bass clarity in mixing depends on several factors,
including how the instruments were recorded.
THE DIFFICULTY WITH BASS
The lowest octave that can be heard (20Hz to 40Hz) virtually has no energy in most
music. The lowest note on a bass has a fundamental frequency of about 41 Hz. So
this first octave contains such things a "room rumble" and the lowest
notes of a pipe organ. The second octave (40 Hz to 80Hz) contains the fundamental
frequencies of the low bass notes and the Kick drum. So this is the first octave
we are really concerned with, unless we are reproducing earthquakes and the like.
This second octave is very difficult to judge, even for the most-experienced
engineers. This is largely due to the speakers we use in listening.
THE DIFFICULTY WITH SPEAKERS
The average speaker that people listen to, does not properly reproduce the frequency
range from 40 Hz to 80Hz. This is true even for many expensive "powered"
speakers. You really can't hear this range of frequencies unless you have awfully
big speakers or a sub-woofer on your system, and a subwoofer that doesn't "accent"
this range. But the difficulties don't end there. Because some speakers don't reproduce
this range, speaker manufacturers often "enhance" the low-end by boosting
the sound output for the next octave (80 Hz to 160 Hz). This makes the speaker sound
like it has more bass response but they are actually substituting extra energy in
this octave for a lack in the lower octave (40 Hz to 80 Hz). This makes it hard
to judge the sound, add equalization, etc. When subwoofers are added to speakers,
there is still the boost in the higher bass octave and additionally there can be
a "hump" around the point where the subwoofer and the speakers are both
reproducing sound (around 100 Hz). The "truest" speakers are those huge
studio monitors that no one can afford except large studios.
DIFFICULTY WITH ROOMS
In addition to all of these problems, you have problems with standing waves that
make the bass uneven in the room. As you walk around most rooms, you will hear more
bass in some spots and less bass in other areas. Usually the bass is louder near
the walls and in the corners of a room. Also, speakers against the wall or in corners
increases bass output. SO WHAT TO DO FIRST? Small speakers don't reproduce the very
low frequencies very well but can become muddy sounding when they try. Therefore
we often filter out the very lowest frequencies as a first step in mastering. We
often will use a 32 Hz high-pass filter, which has the frequency response shown
in figure 1.
FIGURE 2 - 32 KHZ FILTER RESPONSE font>
Even though there are no fundamental frequencies below 40 Hz, there
can be energy in this range caused by "rumble." In addition, however,
the filter slightly reduces energy up to 64 Hz as shown in the graph. This reduction
of the low bass energy has practically no effect on the bass sound except to make
it a bit clearer and make the overall signal a little louder (after adjusting the
level back to normal after filtering).
SO THEN WHAT DO I DO?
It is very necessary that you judge the amount of energy in both octaves
that we have discussed. It is all to easy to "accidentally" have an abundance
of energy in the low bass octave (40 Hz to 80 Hz) that goes "unnoticed"
in your mixing but which makes the whole mix sound "muddy" on a big system
and "low in level" on a smaller system. /span>
My advice for judging energy in this range would be to:
1. Always choose a "reference"
cut from some national artist that "sounds good" and has good "bass clarity" on
all systems. When trying to judge your bass clarity, compare the sound on your recording
with the "reference."
2. Listen to the mix on as many different systems
as possible, including a "big" system or a system with a sub-woofer.
3. Consider strongly adding a subwoofer system
to your monitors, unless the specifications on your speaker show that you have adequate
50 Hz energy.
4. Set up your "near-field" monitors in the room
a. Your speakers are away from the wall by at least18 inches or so.
b. Realize there should be sound-absorbing material on
the wall behind the speaker to prevent reflections from interfering with the "direct
sound." This is especially important if the speaks cannot be 18 inches away from
c. Set up your "listening chair" so it is not against a wall, or in a corner.
d. I have developed a set-up that can be used in many
small rooms that keeps the speakers working well for you (see right
FFIGURE 2 - ROOM SETUP
Another way to judge the amount of energy in the bass ranges of your mix involves
using a Spectrum Analyzer. The spectrum analyzer shows the energy distribution in
each octave. You play both your mix and the reference mix through the device and
compare energy between the two for the ranges we have discussed. There are many
models and many computer programs that will do this for you. The unit we use is
in a program called Ozone by Izotope.
THE CLARITY FREQUENCIES
These bass-frequency instruments have harmonic frequencies that are in the midrange.
This doesn't mean that you can generate these harmonics with your equalizer. It
does mean that when you record you have to capture the harmonics of the instrument.
When you do this, the amount of equalization you have to use will be less and clarity
on your bass will automatically be better. When playing one pitch, instruments put
out energy at the "tuned" frequency, called the fundamental frequency
and also multiples of that frequency called harmonics. In general the harmonics
are responsible for the "distinction" and "tone" of the instrument
where the fundamental provides "pitch recognition" and "power."
As a result, the harmonic frequencies are the frequencies that are the "clarity"
frequencies. Equalization charts often identify frequencies that you may want to
boost on the bass guitar as being 400 Hz, 800 Hz or 1.6 kHz. boosting one of these
frequencies will often make the bass line more distinct and clear. You choose which
frequency to use based on which one works most effectively in the particular mix
you are doing.
More basic to the use of equalization is to make sure that you have recorded sufficient
harmonic frequencies. There has to be harmonic frequencies sufficiently present
in the recording for the equalization to boost. An equalizer does not generate harmonic
frequencies, but simply makes them louder or softer. It is interesting that when
the recording is rich in harmonics, the need for equalization diminishes.
RECORDING THE BASS GUITAR
The bass guitar we record is an electric instrument. It makes sound by sending it
though a bass-instrument amplifier. You can record the bass by putting a microphone
on the bass amplifier's speaker, and you can record it with a "direct"
box, not using any microphone. Alternately, you can record it both ways, blending
the two together. In my experience, the best way to record the bass is is the last
choice. This is especially true for tunes that have a lot of guitar work (like rock)
and when there are horns or low synthesizer parts recorded on the production. In
my experience the amplifier sound, blended with the direct sound, gives you a bass
that can't be killed with lower speaker volumes (see "Fletcher Munson Effect").
In addition the "recommended" equalization seems to have much more effect.
This is due to the harmonic frequencies that are generated in the bass guitar's
RECORDING THE KICK (BASS) DRUM
The Kick drum is a low-frequency drum. It consists of a skin which generates
the "note" and a shell which amplifies the skin sound by actually "generating"
additional sound at some frequencies. We almost always record the back of the drum
(away from the drummer) though a hole cut in the back skin. The drum, by the way,
sounds better when there is an 8" hole in the skin rather than having the whole
back skin removed. Drummers often put a pillow in the Kick drum to "damp"
the skin so that it doesn't "ring out" as much.
1. If possible, use a "dead ringer" type damper rather
than a pillow. "Dead Ringer" is probably a trademark but we are talking about
a strip of foam that has glue on one side. This strip is attached to the shell,
right where the shell and the skin meet. The foam presses lightly against
the shin all the way around the shell and damps skin vibration without changing
the tone of the instrument much.span lang="en-us">
2. Put the microphone at the end of the shell (back
end), almost touching the shell and pointing at the skin. See the diagram on the
right. Make sure that there isn't any damping material between the skin of the drum
and the microphone. - as shown in figure 3.
This way of micing the Kick drum gives you the "shell sound" as well
as "skin sound." The result is that the drum sounds more like a drum,
is easier to hear at low listening volumes and responds to equalization better.
THE REAL WORLD
Recording the bass or the Kick drum correctly makes mixing much easier. In the
real world, however, you will often have to mix things that weren't recorded correctly.
So what do you do then?
Re-recording is a way many professional recording engineers achieve the desired
sound. As an example, lets take the bass guitar. Let's say that you need to mix
a tune where the bass guitar was recorded with a direct box and you want to "blend"
a mic sound that was never recorded. One thing you could do is to send the "direct"
sound from the recorder to a bass amp in the studio. Now as the multitrack tape
plays, the bass amp will get a signal like it would get from the instrument. You
then put a mic on the bass amp and bring the signal back into the console to blend
it with the direct sound.
Another way to achieve the "best" drum sound would be to use good-sounding
samples of drums. You trigger the sampled drum sound off of the actual sound you
have [You send you recorded Kick drum to the "trigger input" of the sample
playback unit, drum machine or keyboard - so that the sample will play only when
the Kick drum you have recorded plays]. The sound you wind up with is a blend of
the "real" Kick sound and the sample.
"BUILDING" A SECOND MICROPHONE
One common electric guitar mic placement technique is to place a microphone 8
inches behind a microphone right against the grill cloth of the guitar amplifier.
One mic is used as the "left" mic and the other mic is used as a "right"
mic. So let's say you have a guitar that was only recorded with one microphone and
you want the sound that would be obtained with 2 mics. You can attain something
close to this by adding delay, EQ and reverb.
My specific recommendations for building that second microphone would be:
1. Put your guitar into two channels of the console,
using a "Y Cord" or some such device. Put a delay on the second channel of about
0.75 ms. (one Kick is about 1 ms. and 8 inches would be about three-quarters of
2. Reduce the high frequencies of the delayed microphone
about 3 dB with shelf response equalizer, using a corner frequency of about 3 kHz.
This simulates the sound traveling though some air before reaching the microphone.
3. Add a slight amount of reverb to the delayed microphone
to simulate the increased "room sound" of the second microphone. If you add reverb
to both mic channels (which you normally would), always add a little more reverb
to the delayed channel.
WHAT'S THE POINT?
Well the point is that the mixing engineer has a lot of techniques that can be used
to get the sound that involve more than just bringing up faders. The professional
engineer working on big budget productions uses techniques like this to get the
sound. The techniques are not that difficult for a home recordist to use, but you
need to know that they exist and that this is how those national records get that