“Multi-Dimensional Processing,” or “MDP” for short, is part of all BOSS compact pedals that have names ending with “X”. Bringing together over 40 years of knowledge, today’s advanced processing capabilities, and the company’s powerful development infrastructure, this true breakthrough technology achieves musical expressiveness that’s impossible to realize with conventional effects technologies. In this article, we’ll explore the complex sound-production capabilities of the guitar, and how MDP technology works together with these capabilities to bring unmatched creative expression to your music.
Preserving Tone Through Sophisticated Processing
Ever since its founding in 1974, BOSS has meticulously researched the sound-making processes of musical instruments, and of guitar in particular. While times have changed and technologies have evolved, the primary goal for this ongoing research has always been simple: to create products that produce the best guitar tones possible.
Among guitarists, the definition of “great tone” is extremely personal, and can vary considerably from player to player. This is because the guitar is such a responsive, interactive instrument that’s capable of nearly unlimited sound variation.
Standard electric guitars can deliver sparkling arpeggios, sweet jazzy tones, bluesy crunch sounds, heavy rock riffs, and many other tones. Extended range guitars with seven and eight strings take things even further. And the sensitive sounds of steel-string and nylon-string acoustics are yet another side of this incredibly versatile instrument.
Guitar type (solid vs. hollow), body wood, and playing technique all have defining impacts on the sound, and even strings, pick type, and string height affect the tone. With electric guitars, components such as pickups, pots, and cables influence the sound as well. Of course, the amplifier that the guitar is connected to has a major impact on the tone. When combined with effects processing, it’s probably fair to say that the guitar can produce more sounds than any other instrument.
The Three Primary Elements of Guitar Sound
You may have learned in school that sound can be divided into three elements, as shown in Figure 1:
Let’s analyze these elements as they apply to the electric guitar:
Pitch
The guitar’s pitch changes according to what strings are played, and the position at which notes are fingered on the fretboard. If the guitar is equipped with a vibrato bridge (also known as a tremolo bridge), the bridge’s arm can change the pitch as well.
Loudness (Level)
The loudness of the guitar is affected by picking dynamics, and also by the volume control on the instrument. Other factors influence the loudness, including the output characteristics of the guitar’s pickups, the pickup height, string gauge, and more.
Timbre (Overtone Structure)
There are many elements that affect a guitar’s timbre, including its type, brand, material, finish, pickup type and position, and tone controls. These elements are intensified when using effects like distortion. Picking strength also affects timbre, especially when the sound is distorted.
As with all sound, the element of time also comes into play. After a guitar string is picked, the pitch, loudness, and timbre all change in a constantly evolving way as the string vibration decays. This complexity is magnified exponentially when multiple strings are vibrating at once.
Other Elements That Affect Expressiveness
There are many additional factors that subtly influence the guitar’s three sound elements, such as pick material, playing with a pick vs. bare fingers, playing the same notes on different strings, and so on. As you play, all these elements interact to produce the guitar’s evolving dynamic response, as shown in Figure 2:
Another important factor is that the overtone structures of low notes and high notes are completely different. And as the sound decays, the volume and timbre of all notes continually change as well. In the case of a distortion sound created by a stompbox, picking harder and physically adjusting the guitar’s volume knob actually has more impact on the timbre than the overall loudness.
This variation in overtone structure is known as “articulation,” and it plays a significant role in musical expressiveness. Simply put, the sense of sound energy is more important than volume level for musical expression.
To illustrate this, imagine the sound of a crash cymbal in a drum set: when the cymbal is struck hard, the sound is always perceived as hard, even if the volume is turned down. Conversely, a soft-struck cymbal is not perceived as a hard sound, even when the volume is turned up.
Optimized Processing for Each Sound Element
In the world of guitar, “great tone” is the result of many, many complex elements that interact with each other in a way that’s pleasing to the player. Conventional processing technology is only capable of a one-size-fits-all approach that’s applied to all the elements at once. In many applications, this can provide the best effect. But when the numerous elements vary considerably, the conventional approach can be quite limiting.
For example, you might dial in a distortion to produce tight and even tone that’s perfect for heavy, palm-muted riffs on the low strings. But when you play that same sound on single-note lead phrases in the mid and high ranges, the tone can be thin and sterile. In this case, optimizing your effect for one style reduces the quality of sound for another. And when you adjust the effect to work better for both styles, you end up with a compromise that doesn’t give you the best sound for either.
This is where the powerful MDP approach excels. An MDP distortion analyzes the level, overtone structure, and frequency characteristics—which vary according to picking dynamics, register, string gauge, chord or single note, wound or plain string, etc.—and then continually adjusts itself to apply the best effect at all times. As a result, your distortion is always completely optimized, no matter what style or range you play in.
Figure 3 provides an illustration of how the MDP distortion works. Conventional distortion is designed with a focus on the “sweet-spot” frequency range, and many overtones present in original signal are lost. MDP detects all the information produced by the guitar and reflects them, so the original rich overtone structure is completely maintained. This preserves the wide-ranging expressiveness of the pure guitar tone, and greatly improves the clarity of the distortion.
But MDP is not just for distortion; it provides superior results for all types of processing, and works exceptionally well for compression. In Figure 4, you can see the dramatic compression improvement with MDP. It shows both the fundamental tone and harmonic overtones of the input signal when a string is picked. Because the overtone structure is more complex and produces more level at the moment of attack, the conventional processing approach compresses the fundamental tone and overtones equally. With MDP, only the overtones are compressed, preserving the fundamental. This provides optimized compression that never squashes your core tone, resulting in natural sound that’s never colored or constrained.
The Quest for Greater Musical Expression
As noted earlier, the articulation defined by a varying overtone structure is key to the musical expressiveness of a guitar sound. Figure 5 compares the overtone structures of conventional distortion and MDP distortion in response to picking dynamics:
A conventional distortion loses some overtones when the picking is soft. And as the picking strength is increased, the distortion introduces high-end overtones that produce muddy resonances not present in the original tone. Conversely, MDP distortion retains all the rich overtones of the original sound, even when playing softly. And when picking the strings hard, both the thick low end and clear high overtones are retained. Since an MDP effect maintains the natural overtone structure of the guitar at all times, the unique musical nuances produced by different players, styles, and instruments always shines through.
As we’ve detailed so far, MDP uses advanced technology to instantly analyze and divide the input signal into many elements, and then apply massive, complicated processing to each simultaneously. Going well beyond a simple snapshot, MDP adjusts its response temporally, continually refining the processing to address the complex tonal changes that happen over time.
In the development of each product where it’s employed, MDP processing is painstakingly tuned with the direct input of top guitarists around the world. A huge selection of actual playing styles have been analyzed to achieve natural and musical response with MDP, which is easily accessible to the user via intuitive stompbox controls. But despite the simple interface, the internal processing is extremely detailed, and many interactive parameters are adjusted to reach the final results.
Figure 6,Figure 7 compares how the internal parameters change on a conventional distortion pedal versus an MDP distortion pedal. Figure 6 shows the extremely simple processing range of the Drive knob on standard distortion stompbox. In stark contrast, Figure 7 shows the sophisticated processing that happens inside the MDP pedal as the knob is turned from minimum to maximum. As you can see, tweaking a single knob moves many parameters to varying degrees. Furthermore, these parameters continuously interact with each other in reaction to what the input signal is doing at any given time.
With its intelligent processing approach, MDP delivers complex results that are simply not possible with conventional technologies. But this would mean nothing if those results weren’t musical, natural, and inspiring to play. To this end, the intelligence in MDP processing is not simply the result of powerful DSP and advanced algorithms; it’s intelligence that’s guided by the massive experience, knowledge, and unwavering dedication of the engineers at BOSS, as well as the input of the world’s greatest guitarists. With this powerful fusion of technology, craftsmanship, and know-how, MDP enables you to express your personal guitar voice like never before.