The researchers have decided to explore a few of the digital effects readily available for post processing audio from an electric guitar, research on what they are, and how they affect the sound quality. The researchers will be particularly looking in the built-in effects in the Mac DAW Garageband for electric guitar, namely Amp Simulators, Auto Wah, Chorus, Flanger, Phaser, Distortion, Overdrive, Fuzz, Vibrato, Delay, and Sustain.
Since the researchers want to study digital effects that are easily accessible for post processing audio from an electric guitar, they decided to use Garageband. GarageBand is a software application for OS X and iOS that allows users to create music or podcasts. It is developed byApple Inc. as a part of the iLife software package on OS X. It is easily accessible because it comes along with OS X, so anyone with access to a mac will have access to garageband. The researcher will be using the OS X version of garageband for mac computers as opposed to the iOS version for Apple’s mobile devices. The researchers used Garageband ‘9 (version 5.1) for this study.
In addition to the standard tracks, Garageband allows for guitar-specific tracks. Guitar tracks can utilize a variety of simulated amplifiers, stomp boxes, and effects processors. These imitate popular hardware from companies known in the guitar and amplification industry, although there is no mention of which specific manufacturers and models by Apple.
Up to five simulated effects can be layered on top of the virtual amplifiers, which feature adjustable parameters including tone, reverb, and volume. Guitars can be connected to Macs using the built-in input (requires hardware that can produce a standard stereo signal using a 3.5mm output) or a USB interface. All digital audio effects used were taken from Garageband’s built-in library.
Digital Effects: Amp Simulators
Modern Stack: Extreme distortion for aggressive rock and metal
Small Tweed Combo: A 1950s American amp perfect for stinging blues riffs or chunky rock chords
Blackface Combo: A 1960s American amp with a bright, balanced tone that shines on clean rhythms or punchy leads
English Combo: A British Invasion Amp know for sparkling highs and biting distortion
Vintage Stack: This powerful British amp helped define classic rock
All of the mentioned amp simulators have the same set of virtual parameter knobs. The only different between each amp simulator is the kind of distortion and the overall tone that you get.
A guitar amp can be thought of as a device that has two stages. A relatively weak signal goes from your instrument into the first stage, where it is processed and handed to the second stage, which boosts it into a strong signal—the sound that then comes out of the speakers. These amp simulators try to replicate this process digitally.
The first stage is the preamp stage. On some amps, you can control the level or strength of the signal sent through this first stage; this control is called Gain (also often labeled as “drive”). Your gain setting determines how hard you’re driving the preamp section of your amp. Setting the gain control sets the level of distortion in your tone, regardless of how loud the final volume is set. What this means is that your gain setting determines how clean or dirty your sound is regardless of the master volume setting.
Master volume is an entirely separate entity that lives in the second stage of your amp, the power amp section. It provides the muscle. The preamp (and gain control) provides the shape of the sound; the power amp provides the overall amplitude of the sound. In the case of Garageband’s amp simulators, this controls the amplitude of the signal after the gain, bass, mids, treble, and presence knobs are taken into effect, and before it hits the reverb and tremolo parameters. The Output knob control the final amplitude of the signal after it has passed through everything.
The bass, mids, and treble knobs control the amplitude of the bass, middle, and high frequencies of the signal respectively. The presence knob controls “presence”. A presence control boosts the upper mid-range frequencies. Thus by increasing the presence with the presence control, the sounds of voices and such instruments seem more “present”.
The reverb knob control the amount of reverberation in the signal, which is the persistence of sound in a particular space after the original sound is produced. It replicates the effect created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is reflected off the walls
The tremolo knobs control trembling or “shuddering” effect produced by slight and rapid changes in the volume (amplitude) of a note. The tremolo rate control how fast the amplitude modulates and the tremolo depth control by how much.
Digital Effects: Stompboxes
The sustain pedal is labeled Squash Compressor because it compresses the signal on the sound. It adds an effect to the note or chord to make it sound like it lasts longer.
The sustain setting, will bring down the high amplitude signal parts of your chords or notes. This can make parts sound more level with the rest of the chord.
The level knob is increases the over all volume of the signal. This can be used to increase amplitude lost from the sustain setting.
The delay pedal incorporates time, repetition and mixing effects to create an echo sound within the audio.
The Time knob controls the time delay between the repetitions of the notes in milliseconds. When the Sync button is enabled, the time knob changes to standard note values, dotted notes (d), and triplets (t) in accordance with your project’s tempo.
The Repeats knob adjusts how many repetitions are in the delay.
The Mix knob controls how intense the effect is. You can adjust how much of the delay effect is mixed into the original audio signal. A low mix will make the echoes softer, while a high one will make it louder.
The Auto-Funk (auto-wah) pedal in similar to the wah pedal in that it brings the audio signal in and out of a low-pass or bandpass filter response, resulting with a “wah wah” effect. Instead of the effect being controlled by a foot pedal, as on a standard wah-wah, the effect alters in response to the volume of the input signal.
The Sensitivity knob controls the sensitivity of the pedal’s reaction to signal amplitude. If you lower the sensitivity you’ll have to strum the guitar harder to get an effect. If you raise the sensitivity you don’t need to play as hard. This changes the burst of in-and-out effect the pedal produces.
The Cutoff knob adjusts filter’s cutoff frequency. It determines the cutoff point at which the effect will apply to the audio.
The auto-wah can further be adjusted through the additional sliders. The BP LP allow you to choose between a bandpass and low-pass filter respectively. The HI LO refers to the high and low frequency resonance of the filter. The UP DOWN slider give the options for sweeping the filter up or down.
The Vibe pedal creates a pulsating sound effect produced by slight and rapid changes in the pitch (frequency).
The Rate knob adjusts how fast the pitch modulation is in Hz. Raising it creates a faster rate, while lowering it creates a slower one. When the Sync button is enabled, the time knob changes to standard note values, dotted notes (d), and triplets (t) in accordance with your project’s tempo.
Tremolo Depth controls by how much the pitch modulates. The Type knob changes the specific type of vibrato effect.
The Grinder pedal adds a distinct, gritty distortion to your audio track.
The Grind knob changes how much distortion is incorporated into the audio. Turning it up will produce a heavier grind sound, while turning it down produces a weaker one.
The Filter knob adjusts the filter being applied. Setting it low applies a low-cut filter and setting it high applies a high-cut filter. The Full Scoop switch enables and disables the filter. Setting it on full disables the filter knob completely.
The Level knob controls the final amplitude of the signal.
The Vintage Drive pedal are mimics class overdrive pedals which are boosters with some clipping circuitry. For the most part they are only meant for “mild” distortion
The Drive knob controls the level of preamp gain, thus, controlling the level of distortion. Increasing the drive will produce a higher level of distortion.
The Level knob adjusts final output level.
The Tone knob adjusts the tone of the effect by adjusting certain frequencies. The tone can be further adjusted by activating the Fat switch, which adds lower frequencies to the effect, making the overdrive sound fatter.
The Fuzz Machine pedal is an effective way to give your audio a fuzzy, distorted sound. It alters an audio signal until it is nearly a square wave and adds complex overtones by way of a frequency multiplier.
The Fuzz knob changes how much fuzz/distortion is incorporated into the audio. Turning it up will produce a heavier fuzz sound, while turning it down produces a weaker one.
The Level knob adjusts final output level. The Tone knob adjusts the tone of the effect by adjusting certain frequencies.
The Retro Chorus add a chorus-like feel for your audio track.
The Rate knob controls how fast the chorus LFO’s speed (in Hz or tempo (if Sync switch is activated). A higher rate will create a faster back-and-forth sound.
The Depth knob adjusts the depth of the LFO. It will determine how big or drastic the pedal’s effect is.
The phaser pedal works to slightly cancel out the audio signal and create a muffled, warped sound. It’s modeled on phasing issues that occur in the audio world. When sound is “out of phase,” its audio waves are being cancelled out by opposite ones.
The phaser pedal only slightly cancels out the waves and creates a distinct audio effect.
The Rate knob controls how fast the effect goes in and out of the audio. A faster rate will speed this up, while a slower one makes the process more gradual.
The Depth knob adjusts the degree by which the audio signal goes in and out of phase.
The Feedback knob controls how many repetitions will occur in the effect.
The Robo Flanger pedal adds a mixture of both the delay pedal and phaser pedal effects to your audio, but it has its own distinct sweeping sound.
The Rate knob will change how fast the effect goes back and forth.
The Depth knob controls the depth of the sweeping effect.
The Feedback knob controls the repetition of the end of the audio signal and intensifies the sound.
The Manual knob adjusts the amount of time delay in the signal and works similarly to the delay pedal only in lesser time values.
Lee Jackson (2008). Ultimate Bench Warrior. Music Dispatch. p. 75.
The Boss Book: The Ultimate Guide to the World’s Most Popular Compact Effects for Guitar, 2002, Hal Leonard Corporation
Holmes, Thom (2006). The Routledge Guide to Music Technology. CRC Press. p. 177.