The Electronics Behind Musical Instruments
What do you get when you drop a piano down a mine shaft? A flat minor.
If you didn’t get that reference, fear not for you’re among the thousands of musicians and people who don’t focus on music theory. But if artists don’t know the theory how do they create such glorious sounds you may wonder. Well, they obviously use instruments just as Apollo used the lyre or the Pied Piper of Hamelin. But let’s look at the fundamentals first. What is sound? From the perspective of physics, a sound is a vibration that propagates as an acoustic wave, through a transmission medium. But to your everyday Joe sound is just the reception of such waves and their perception by the brain. Now that we have established what sound is, have you wondered why instruments make the sounds they do? Let’s take 3 of the most frequently used instruments in modern-day music — the electric guitar, the keyboard, and the electric drums.
Electric Guitars and Amplifiers
We all love the sight of a guitarist charming a crowd on a summer morning and the sweet melodies that are spun through the plucking of strings. Now imagine you’re a particle present within the cavity on the body of the guitar body, known as the soundhole. As soon as the artist plucks the string you feel an immense energy flow through yourself and hence you move or more specifically you vibrate at the same frequency. And as you and your fellow particles all vibrate in unison within the soundhole, you amplify the initial amplitude of the wave and hence create a melody by acting as a natural amplifier. But you may wonder how legends like Jimi Hendrix or Slash create such loud and powerful sounds as their electric guitars don’t have soundholes. On the bodies of electric guitars, you’ll find the usual strings and tuning heads at the end of the neck. But you also see a variety of elongated cylinders with metallic circles on them and a bunch of knobs. These circles are responsible for the capturing of the mechanical waves and converting them into electrical energy and they are nothing but inductive sensors. These sensors at the very base are magnets wound with conducting wires. The phenomenon of electromagnetism is the key behind the functioning of electric guitars. The metal strings on being plucked vibrate and create a variation within the surrounding magnetic field. This induces an electromotive force which is passed on through the circuit and to the amplifier or other effect pedals. Now amplifiers, as the name suggests, are responsible for the amplification of the incoming electric signal. A guitar amplifier is primarily made up of 3 parts — the preamp, the power amp, and the speaker. The preamp is responsible for controlling factors such as distortion, bass, treble, mid, volume, and more. Depending on the case, the circuitry within the preamp is adjusted and the input signal gets modified before it is then passed on through to the power amp. The power amp on receiving the signal outputs a significantly larger version of the input signal with voltage high enough to drive a speaker. And the speaker, as any other transducer system would, converts the larger signal from electrical energy into mechanical energy ergo sound.
Microphones work just as a speaker would but the transducer system operates in the opposite direction with a diaphragm within the microphone converting the mechanical energy within the vibrations produced in the air columns into electrical energy which again go through several circuitry and modifications.
Keyboards and MIDI Controllers
Digital pianos or more commonly known as keyboards are pianos that can make the sounds of any instrument and animals too. Keyboards comprise of keys with different pre-registered signals for each key. Each signal varies in frequency in order to provide a wide range of sounds. The keys use pressure sensors in order to know at what velocity and for how long the signal should be projected for. These days there has also been a rise in optical sensor-based keyboards. They use infrared technology to sense the velocity of a key rather than interpreting its impact pressure. And the quality does bring a hefty price tag. Since the keys have pre-registered signals a variety of sounds can be produced from a single key all within the same frequency range. But the sensors and other systems matter only as long as the speakers on the device are powerful as there is no use for the processed input without an output system and hence digital pianos have speakers with massive diaphragms.
MIDI Controllers are keyboards with extra modules in order to have a higher degree of additional effects and modulations. MIDI Controllers more often than not don’t have their own speakers. This can be explained using the full form of the abbreviation MIDI which stands for Musical Instrument Digital Interface. The MIDI controller is hooked up to a computer and it works by sending MIDI signals to the system. These signals can be edited or modified to sound like a completely new instrument only limited by the artist and creator. MIDI controllers often have more than just keys. They have pads to which the artist could assign sounds and cut them up and sample them. When you press a pad, it creates a MIDI message which is sent to the device to be modified, saved, or more.
Electronic Drums
If you think your neighbor’s drum kit is a nuisance, recommend an electronic drum kit to them. Can’t change your neighbor but if you can slightly change the way they create, you’d get a few more hours of sleep in. Electronic drums are mesh head drums with rubber pads with sensors beneath them. A rubber pad could be assigned a certain sound such as the sound of a cymbal, hi-hat or bass drum. On hitting the pad, using the transducers drum triggers or trigger pads send signals to what is commonly known as “the brain”. The brain has all the presets and on receiving a signal from a trigger pad, the brain sends the respective sound signal to the output source. And that’s where the electronic drum stands ahead of a classic mesh head kit — the output can be sent to any number of audio-based output devices and they can also be recorded and saved. This provides not only artists but even beginners the freedom to practice with sessions from the past and other tracks.
The music of today is nothing like that of yesterday. Comparing pieces by Bach and Jacob Collier — they’re both melodic and complex but they’re also vividly different. This is the analogy I’d use to compare the instruments from around a decade ago to the instruments of the present day. The technological advancements in the area of music production have grown severalfold. And as the tools get significantly abstract, so do the abilities of the creator. Thence the power of music and art is limited only by the limits of the vast universe of physics and by those that an artist would design for themself.
Enjoy jammin’!
Written by Aaron Varughese, Core Committee Member of IEEE CAS, VIT
