WHAT IS SOUND?
In its most basic form, Sound can be described as a wave, formed by a vibrating object. Such as an instrument, oscillator, string, drum membrane or tuning fork.
WHAT IS A WAVE
A sound wave can be perceived as some form of disturbance that travels through a medium, for us this medium is air. If the wave isn’t constant it may also be known as a pulse.
When a sound is formed from a vibrating object, the waves move parallel from the sound source in a longitudinal manner. The way the sound moves causes air particles to compress and rarefact. (push together and pull apart) this change in air pressure is what is perceived by the human ear as sound.
A good way to visualise sound is to imagine a pond, when it rains, a drop of water will hit the pond (this can be thought of as our vibrating object or source)
This will create a sound wave, (recurring pulses) which will propagate (travel) through the water. This can be seen happening by the ripples in the pond that can be thought of as longitudinal waves of compression and rarefaction (changes in air pressure).
WHAT IS A VIBRATING OBJECT
You may ask yourself, how do we know what a vibrating object is? Well any form of sound source will be a vibration in some form or another.
· Human vocal chords and mouth creating pressure variations
· A snare drum’s skin vibrating when hit with a beater
· A violins string vibrating
· A mallet instrument such as a glockenspiel resonating when hit
· A synthesizer using oscillators to create sound, which creates electrical signals that can be used as vibrations to create sound
· A tuning fork being struck, causing vibrations in the prongs
For these waves to sound musical they need to be periodic. This simply means that they need to be repetitive regular cycles. If they are non-periodic they are more likely to sound dissonant (inharmonic) which is a characteristic of metal, glass and some types of drum sounds.
The rate at which air pressure changes is known as the frequency of sound, which is measured in cycles (waves or pulses) per second. This is measured in Hertz (Hz)
Frequency also directly correlates to pitch. A4 on the keyboard being 440Hz. Instruments can be tuned differently but most instruments will be tuned to this standard concert pitch.
After some time working with frequency and pitch we will start to learn and understand troublesome or useful frequency ranges. For example, many club sound systems are tuned for maximum impact around 48 – 55Hz, which equates to G1 – A1 on the keyboard. This can be useful when deciding the pitch of the kick drum and bass parts and their interplay.
DIFFERENT WAVES & HARMONICS
Now that we understand what a wave is, it’s fairly easy to figure out that there are many different wave shapes. These different shapes will give us a completely different tone even though they may be the same pitch.
The simplest and purest wave is the sine wave. It is known as a pure tone because it contains no harmonics (extra frequencies). This means that it is made up of only one periodic wave. The frequency of this wave is known as the fundamental frequency (which is also its pitch).
Due to the fact that it only has a single frequency, we can understand that filtering this sound will have very little effect other than to attenuate the signal when the filter cutoff starts to get close to the fundamental frequency.
The reason for this is because if there are no harmonics for the filter to remove then there will be no change in sound.
The reason the sound will slowly attenuate at the cutoff would be because the filter slope will start to take effect on the fundamental frequency as it gets close. (The sound will get quieter at a rate that is the same as the filters slope) A standard filter slope is usually 12 or 24dBs per octave.
HARMONICS & TIMBRE
A sine wave at 440 hertz (A4) will sound very different to a piano or violin at 440 hertz. This is because the piano and violin sounds are made up of multiple waveforms. We can think of these complex waveforms as being lots of simple ones combined together to form an overall richer sound.
These extra waves may have completely different Frequencies, phases, and amplitudes. All of these factors combined together will contribute to the complete sound. These extra frequencies are commonly known as harmonics, overtones or partials. (They each have some form of mathematical relation to the fundamental frequency if they are harmonic) If they are dissonant (inharmonic) this is not the case.
When we are measuring partials or harmonics we need to remember that the fundamental frequency still counts as a partial.
A partial which is an integer multiple of the fundamental frequency is known as a harmonic. This means that the partials frequencies will fit directly into the fundamentals wave by X amount, or in other terms, the two waveforms will slot together by whole integer ratios which make them sound ‘in tune.’
Here we can see how each harmonic fits into our fundamental frequency by a given amount. A doubling in frequency represents one octave. So here we can see that if 440Hz is the fundamental frequency, then the second harmonic in this case will sit at 880Hz, which fits into the fundamental twice a ratio of ½). This will be A5 on the keyboard.
The third harmonic fits into the fundamental three times, 440 + 440 + 400 = 1320Hz. This creates an interval of a fifth (this frequency is an octave and a fifth above the fundamental), which is a frequency of 1.32KHz or E6 on the keyboard.
The fifth harmonic fits into the fundamental five times, This creates an interval of a third (this frequency is two octaves and a major third above the fundamental) which is 2200Hz or 2.2Khz. This is equal to C#6
This shows that we can create a basic square wave with as little as just 3 sine waves stacked on top of each other. This is the basis for Fourier’s harmonic series.
These extra overtones are created because a harmonic oscillator, such as a column of air or a string in the case of musical instruments, can and does oscillate (vibrate) at numerous frequencies simultaneously.
In pitched musical instruments, these overtones are usually harmonic due to the nature of resonance, which basically means that pitched instruments will cause harmonic frequencies to sum together and inharmonic frequencies will cancel each other out to some degree. This will give us an instrument that creates an overall harmonic sound.
This set of harmonic frequencies is known as the harmonic series. Our brain defines this as being musical due to its correlation to the chromatic scale.
ABLETON OCTAVE ERROR WARNING
Be aware that within Ableton Live, the spectrum analyzer will appear to be an octave out of tune (A4 = 880Hz instead of 440Hz). This is because Ableton have opted for a Japanese midi octave designation instead of the more commonly used scientific tuning. This is just something to be aware of if you are wondering why the octaves are not lining up with other pieces of equipment. Other than the labeling this will have no other effect. Pressing A4 on the keyboard will still result in a 440Hz tone.
Timbre is a combination of all of the different amplitude, phase, balance and ADSR relationships of all of the harmonics in relation to one another. This is what will define the colour and character of our sound, which is what we perceive as tone or timbre. This is also how we can tell the difference between a sine wave and a piano.
INHARMONIC FREQUENCIES AND DISSONANCE
Not all instruments are pitched or relate to the harmonic series. For example an 808 kick drum (and most kick drums) rely heavily on a sharp sweep in frequency, usually from the KHz range down to the 50Hz area, this gives us a powerful punchy impact to our kick drums.
Its important to understand that these instruments may not have a definitive pitch, but they can still be pitched to some degree, especially with elements such as kicks, claps, toms and bongos. We will usually find that by altering their adjustment in semitones or cents there will be a position where they lock into the mix. This is the point where the dominant or sustained frequency is in key with the rest of the mix. This may not necessarily be in the root key of the track. Instruments that generally lack any form of harmonic structure are sounds such as hats and cymbals, which are full of inharmonic overtones and are quite easy to synthesize with nothing more than white noise.
WHAT IS EQ?
EQ is a fundamental tool in the mixing engineers arsenal and can be thought of something that allows us to adjust the tone of our sounds by either boosting or attenuating the amplitude of specific frequencies. This is necessary to help our elements fit together into the mix.
A graphic EQ is a logical way of explaining EQ because it is effectively just a set of volume faders (Much like on a mixing console) but each one is set to a specific EQ range. This allows us to alter the tone by boosting or attenuating the gain at any given frequency. More complicated EQs allow us much more control, which will be explained in the ‘types of EQ’ section.
Many amateur producers disregard just how important EQ is. If used properly it can really add a sense of power to our mix and give each instrument its own space to stand out from the crowd. Furthermore, correct and precise use of EQ will ensure that only useful frequencies are left in the mix to be heard. By removing any frequencies that don’t contribute to the mix as a whole, we will be giving ourselves extra headroom, which equates to a louder final mix without any harsh, muddy or flabby resonances.
Essentially an EQ is a filter, or set of filters, that allow us to alter the tone of the signal. Within the world of EQ, filters can also boost as well as cut frequencies.
There is a wide variety of EQ types, ranging from single band EQs, right up to multiple band parametric EQs. Fundamentally they all do the same job by changing the amplitude of selected frequencies.
WHY USE EQ? – FREQUENCY MASKING
Frequency masking has already been covered in the psychoacoustics section of book 1 in this Zero To Hero Mix Series, however we will briefly recap in terms of why this is relevant to EQ.
Frequency masking is when two signals with similar frequency ranges sound at the same time causing us to only hear one sound, or partially hear one sound, due to the other one dominating the mix.
A good way of explaining this is to imagine being in a busy street with music playing in a nearby shop.
A bus drives past, as the bus passes we can no longer hear the music from the shop. The music in the shop is being ‘masked’ by the sound of the bus.
This effect can be heard to a greater or lesser extent depending on variables such as the loudness of each noise, and the frequency range of each noise.
Full spectrum sounds such as white noise will do a fairly good job of masking any other noise. This theory can be understood much better by using a spectrum analyzer. This will easily highlight which sounds are likely to mask others, purely by looking at the area of the spectrum analyser covered.
In terms of this happening within a mix, imagine a percussion loop that’s occupying a lot of mid and high-mid frequencies. When played at the same time as a vocal loop this percussion is likely to have overlapping frequencies. Because of this we perceive the vocal as being duller or less present because our percussion loop is drowning it out.
This is caused by our ears being desensitised to the sound of the vocal because the percussion is in the exact same frequency range. However if we solo the vocal we will find that it sounds present and bright, likewise, if we solo the percussion we find that this also sounds very professional.
Its only when we sum the two together that the masking occurs which is why EQ is so prevalent within mixing and also why a good mix engineer will pay particular attention to how sounds interact with each other and the relationship between each sounds frequency content, rather than just applying EQ in isolation, which has very little benefit to a entire mix in context.
This sort of scenario can be rectified with some creative sound shaping, which might involve making each of the parts sound a lot worse when in isolation, yet have them working in cohesion when played simultaneously.
EQ FUNDAMENTALS KEY POINTS
- Sound can be described as a wave causing changes in air pressure
- Sound is caused by a vibrating object, the amount of vibrations per second determines the pitch
- Periodic waves will have a tuned pitch whereas irregular vibrations will sound dissonant
- Most club sound systems are tuned between 49-55Hz
- A complex sound is made up of many waves of varying frequency combined together, this is because of micro-vibrations within the vibrating object
- A sounds timbre will change dramatically dependant on the amount, frequency, phase and amplitude of its harmonics
- Frequencies that fit into each other by whole integers will sound harmonic
- Ableton uses an unusual octave range system resulting in 440Hz being labelled as A3 rather than A4
- Dissonance is often used as a sound design tool to make sharp and punchy tones. This is often the case with snares, hi-hats and drums
- The process of EQ can be thought of as similar to balancing, but rather than balancing each tracks fader level, we are adjusting the different tone ranges of each individual track
- EQ can be used to make a part that is dull sound more prominent, or to make a part that is sticking out of the mix blend in
- EQ can be used to help parts sit beside each other without frequency masking which will vastly improve mix clarity
- Masking is affected by the amplitude and frequency range of both the sound being masked, and the sound that’s masking.