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Andrew McDonough
12/16/13
WRIT 340
Professor Townsend
Capturing the Perfect Electric Guitar Sound
Introduction
Have you ever wondered how Synyster Gates creates his dark, overdriven tone for
Avenged Sevenfold, or how Jimmy Page's guitar floats through melodic oceans in "Stairway to
Heaven?" In fact, the main goal of many guitarists is to attain what they call their "perfect sound"
through a combination of specific gear and effects, whether it be the soft, full tone of a jazz
musician or the hard, gritty overdrive of a grunge guitarist. Many spend years, if not decades,
searching for these sounds through experimentation with guitar and amp combinations or the
purchase of the same effects pedals their guitar idols use. However, perfecting ones sound is a
mute endeavor if that sound can never be properly captured and delivered to your listeners in
your desired medium.
The Recording Process
Besides from worrying about all of the factors associated with guitar construction and
effects chaining, one must also keep in mind the steps involved in getting their sound from their
guitar to the ears of their listeners. This is where the recording process becomes vital, as the
sound an artist hears while practicing will never be heard by a listener without using the proper
techniques and equipment. The multiple steps of the process are linear, meaning that each
previous step affects the outcome of each and every subsequent step. Additionally, most of the
variables are not controlled by the guitarist, and, in fact, are influenced by the recording engineer
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assigned to the recording session. Thus, it is important for the guitarist to communicate how he
wants his guitar to sound for the engineer to properly place microphones and process the guitar
recordings. There is a large amount of equipment and technology encountered during the linear
recording process, so this article will briefly explain the major points.
Audio Signal Path
Amp
Microphone
Cable
Recording
Equipment
Mix
Playback/Speak
er System
Figure 1
Referenced: A. Garver
The Amp: The choice of amp, although not normally regarded as part of the recording
path, is the first piece of equipment standing between the guitar's electrical signal output and the
conversion to physical sound. An important term to be familiar with when talking about audio
and its reproduction is the frequency response of a certain piece of equipment. The frequency
response is the output level of a device at different frequencies in respect to the original sound
(i.e. the lows are exaggerated while the highs are cut). The speaker cabinet, or the enclosure that
houses the speaker, will have a characteristic frequency response that will not be flat. This is due
to the materials used to construct it, its size, and its geometry. As a general acoustic rule, dense,
porous surfaces tend to absorb more high frequency sounds while non-porous surfaces tend to
reflect sound and retain the higher frequencies. Additionally, the dimensions of the cabinet can
create a resonance in certain frequencies, which means that a select number of frequencies will
be amplified simply because of the layout of the cabinet. Thus, each cabinet will stress a
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different part of the sound, be it the middle or low end or somewhere in between, and create a
different overall tone [4].
The electronics within the amp, specifically the type of amplification, will also play a big
part in the coloration of a guitar's tone. The
amplification circuit is usually all solid state
Suggested Audio: Distortion through
tube amp versus solid state amp.
(meaning it uses all modern electrical components) or tube driven (meaning it uses a physical
tube for amplification). When the gain, or volume added to the original input signals, of the amp
is turned up, the input signal becomes too strong for the electronics or tube to handle and distorts
the signal. This distortion is a common effect applied to modern guitar's, adding the crunch and
bite to sounds all the way from Led Zeppelin to the Foo Fighters. A tube acts differently than
solid state electronics in this situation, and adds what most consider to be a more organic tone
[13].
There are also built-in effects included with almost every modern amp. These effects are
usually part of a standard set, but, like standalone effects pedals, have their own unique sound.
The most common included effects are called reverb, chorus, distortion (which adds a large
amount of gain to the signal as
explained before), and onboard EQ.
These effects can be combined in
Figure 2: Example Amp Head
series to varying degrees in order to
create the desired final sound of the guitar.
The Microphone: The microphone used to capture the sound of your guitar is the most
influential devices between your amp's tone and the sound that is eventually captured in the
recording. Different types of microphones offer different frequency and transient responses. The
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transient response of a device is how fast it reacts to incoming signal, which is analogous to how
fast one's reflexes are. If something is thrown at you at a high speed, the better your reflexes are
the more likely you are to catch it. Likewise, the greater the transient response if a microphone,
the more likely it is to pick up a very fast or short-lived sound signal [4]. To the right is an audio
clip made using the common makes and models of the
Suggested Audio: Microphone
Comparison
three types of microphones: dynamic, condenser, and
ribbon. Listen to how each microphone, although in the same position, captures a slightly
different sound.
Additionally, different types of microphones have different sensitivities to sound. All
microphones initially output a low level signal that needs to be amplified in order to be used by
other devices. The initial, or pre- amplifier, used to accomplish this is called the preamp. The
lower the sensitivity of a microphone, the smaller the initial signal it produces. Since the
environment will always add noise to your signal due to electromagnetic interference in the
electronics, a low sensitivity brings the desired signal closer to the amplitude of the noise, or
what is called the noise floor [4]. Thus, in order to have the cleanest sounding recording, the
microphone with the highest sensitivity should be used. There are trade-offs to this, however,
such as the irregular frequency response of microphone types with better sensitivity.
Table 1: Microphone Characteristics Overview
Type of Microphone
Dynamic
Condenser
Ribbon
Frequency
Response
Erratic, depends on
mic. Mids are flat.
Almost flat, less lows
Mostly flat
Transient Response
Sensitivity
3
2
1
2
1
3
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Microphone placement is also vital, further affecting the frequency and transient
responses of the microphone. To give a broad view of the subject, the angle of the mike towards
the cabinet, the placement in relation to the speaker cones, and the distance from the microphone
to the cabinet all effect the sound that is captured by the microphone [3]. However, there is a way
around the traditional use of a microphone. Most high quality amps now contain a "direct out"
output jack, which bypasses the built-in speakers and sends the signal, after it has been amplified
and after effects have been applied, directly out of the amplifier. Although it can be argued that
this outputs the "true" output signal of the guitar lacking the added color and specific frequency
response of the amp's speaker, many artists prefer the tone added by their amp and opt out of
using this method.
Frequency Response at Different Angles for a Condenser
Microphone at 30cm
Figure 3: Source-2011C Twin Diaphragm
The Cables: Most guitar players use any 1/4" unbalanced cable they find lying around as
their guitar cable, which i s the standard cable used to connect a guitar and amp. While this suits
jam session and practices, the signal to noise ratio, meaning how much noise or unwanted signal
you pick up in your wires versus how much of the original signal you have, can become a serious
issue in the recording process. This is because unbalanced cables inherently pick up external
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noise due to their construction, the opposite of the
balanced XLR cables used to connect to
microphones or TRS cables used to route audio
signals. This external noise can be the "shhh" sound
often associated with the background noise of a
song or the 60 cycle hum of the adjacent wall
Figure 4: TRS and 1/4" Unbalanced Cables
Referenced A. Garver
power socket [4].
Balanced cables get around this sound issue by carrying two copies of the signal they are
transporting, one that is "hot" (+) and one that is "cold" (-). The hot and cold signal are inverses
of each other, as one is flipped (made 180 degrees out of phase) within the electronics of the
outputting device. For simplicity one can imagine two cosine waves, one starting at a positive
amplitude and the other starting at a negative amplitude. As the signals run along the wire they
both pick up the same noise, which for simplicity can again be a cosine wave. Once the signals
get to their destination, the one that was flipped is flipped back, making the signals add together
but the noise (which now consists of an in phase component and an 180 degree out of phase
component) cancels.
Additionally, the circuit formed by the cable (which has some capacitance) and a passive
set of pickups (which have inductance) will naturally create a low pass filter while also bumping
the middle frequency range. The effect is less and less high end the longer the cable is run, with a
constant middle "bump" [11]. High end cable manufacturers focus on solutions to these
problems, but sometimes the extra color added by the cable can constructively add to your sound
and does not want to be "fixed." The maintenance of sound "defects" starts to be an overarching
trend in the recording process.
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Recording Equipment: Additionally, all the equipment you run your signal through,
from the preamp to analog to digital converter, adds its own characteristic sound to the signal.
This is due to the complicated physics behind how electrical signals interact with device
components, and allows each piece of equipment to slightly modify the sound as it passes
through. These changes are further modified by the strength of the signal. As an example, a
preamp can sound much different when it is turned all the way up to when it is only turned up
half way. The changes are usually minute, but noticeable to a trained ear.
An interesting example of this occurred in a loudspeaker factory in Scotland in the
1990's. In an attempt to find a common amplifier to use with the company's new line
loudspeakers, they brought in recording engineers to listen to different amplifier and speaker
combinations. Although the speakers were different sizes, they were constructed similarly and
thus the engineers expected to find a single amplifier that would produce the best sounding audio
output from all of the speakers. After conducting blind tests of each speaker and amplifier
combination, a different amplifier was paired each speaker except for one case [10]. This
exemplifies the slight variations in how different devices modify audio signal. Many recording
engineers take advantage of these differences and discover their own favorite combinations of
microphones, preamps, and gain staging (the amount of gain added at each "stage" the signal
goes through) that yield their preferred sound.
Mix: Now the analog sound is recorded into digital information and finally captured in a
medium where it can be faithfully reproduced. Yet, there are still more options for modifying the
sound even further. There are a few standard tricks used
by recording and mixing engineers that produce
Suggested Audio: Two mics panned
center, then panned in stereo.
consistent, positive results if desired. One of them is sending separate recordings of your
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instrument using different mikes to different speakers, usually sending almost all of one to the
left speaker and all of the other to the right. This adjustment of how much output signal goes to
each speaker (either left or right) is called panning [12].
Duplicating a single guitar track to make two tracks is another common method.
Separate filters can be applied to each track to only let lower or higher frequencies through, and
then they are panned left and right. This can make the sound of the guitar thick and huge, as the
sound seems to come from all around. Filters can also be used to get rid of certain annoying or
distracting frequencies in post-production to make a bass drum sound less tin-like or to cut out
the 60 cycle hum mentioned earlier. Another use for duplicating tracks is adding effects to the
duplicated track but keeping the original track the same, allowing the duplicated track with the
effects to be dialed in however much is desired. This results in a fuller sound in contrast to
simply applying the effects to the original track and essentially losing a portion of the original
signal due to the effects processing [12].
While guitarists usually add effects much before mixing process, those same effects and
more can be added while mixing. However, these effects will have their own characteristic
sounds that will be different than the effect on the guitarist's amp or in his effects pedal. Thus,
effects like added gain or reverb are usually configured before the recording process by the
guitarist. For other instruments that do not have effects such as reverb and chorus right at their
fingertips, they are added during the mixing process. The most common effects added during
mixing are reverb to any vocal tracks present and compression to the drums and bass.
Playback Device/Speaker System: The device your recording is being played back on
can also drastically affect the sound of your instrument. All speakers systems have a
characteristic frequency response just like the amps explained earlier, and this response is never
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exactly flat. Thus, the final conversion from digital audio to analog sound waves can further
modify the tone of the resultant sound. The human ear naturally accentuates the middle
frequencies, leading many manufacturers to add a built-in, permanent bump in the high and low
frequencies in the hardware of their speaker systems [4]. Meanwhile, the mix of the song is done
in a recording studio in the best possible acoustic environment using the best possible, flat
frequency response speakers. Many times, the manufacturers permanent EQ detracts from the
original mix of the song and forces consumers to listen to a modified version of the song.
Conclusion
Recently, the music industry has seen the development of new technology that has
changed the way the industry works. The rise of home studios and laptop music production has
downplayed the recording process in favor of relying on superior hardware and music made
entirely within a synthesizer program. Also, new technology has been developed that has made
the pure, exact replication of tone possible. An example of this includes the new optical pickup
system by Lightwave Systems that uses light sensors and infrared light to pickup guitar string
signals [9]. However, many artists and engineers favor the imperfections in an instrument or
device that make the sound unique rather than a perfect reproduction of what the signal is,
maintaining the importance of the recording process in music production.
The capture of the perfect sound is a complex and multifaceted project that encompasses
physics, materials science, and utilization of recording techniques. When it comes down to it,
however, the perfect sound is highly subjective in nature. It is influenced by an individual's genre
of choice, playing style, and personal preference. In the end, no two people will have the same
perfect sound, and it will always remain a guitarist's mission and passion to cultivate their own.
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Additional Content:
Author Biography: Andrew McDonough is a junior electrical engineering major pursuing a
minor in music recording. He is a member of the Trojan marching band and the USC IEEE
chapter in addition to being a researcher at the Space Engineering Research Center.
Abstract: The recording process is a multi-stepped linear modification of audio signal in its
analog and digital forms that greatly affects what sound is captured. This process includes the
type of amplification used on the signal, the microphone and its positioning, the cables used to
transport the signal, how the audio is mixed, and what it is played back on. Each of these areas
follows acoustic and electrical circuit laws that inevitably modify the signal at each point in the
chain. The coalescing of the contributions from each step creates a unique tone for each
recording, which can be tailored towards a recording's genre or a musician's personal preference.