UNDERSTANDING SPACE IN SOUND: THE FREQUENCY SPECTRUMSound lives in a limited space. Human ears can hear frequencies from 20 Hz up to 20 KHz. The frequency is tied to the pitch of a sound. The higher the pitch the higher the frequency range. For example, a sub bass might be dominant in the 20Hz- 250 Hz frequency range. A hi-hat or a cymbal will be more dominant in the higher frequencies range between 2 KHz – 12 KHz. On your left is a breakdown of the spectrum ranging from sub frequencies to high ones.
THE 5 BUILDING BLOCKS OF A SYNTHIt might be intimidating to look at a synth with all its buttons laying over everywhere. However, it gets much more accessible and easier to read once you look at a synthesizer as a bunch of separate modules put together.The trick here to not get lost and discouraged learning a synth is to find the delimitations/boundaries of each module (see image below).
Example of a SynthesizerGenerally, you will see a bunch of knobs delimited by rectangles. Each rectangle represents a different module of the synth. The basic modules of a respectable synth are:
- OSCILLATORS (VCO)
- AMP (VCA)
- FILTER (VCF)
1. SOUND DESIGN MODULE #1: VCOThe Oscillator outputs a basic and raw electric waveform that produces a sound (see figure 1.1.1).
- Source: You can select the type of the oscillator waveform. Each waveform generates a different tone and timbre. The basic waveforms you can find on the majority of synths are:
- Sine wave: very smooth. Generally called a pure tone as it generates a single harmonic and doesn’t eat a lot of space. It is perfect for generating bass sounds for example.
- Triangle wave: Smooth, plucky with more harmonics than the sine wave and less than the square wave.
- Square wave: harmonically rich, this is the most aggressive waveform.
- Sawtooth wave: harmonically rich, this is the most aggressive waveform.
- Frequency: adjusts the frequency (pitch) of the sound-wave. In other synthesizers, you will find a knob called Range (or Octave) which purpose is to go up or down by an octave or more.
2. SOUND DESIGN MODULE #2: VCAYou might think of an amplifier as a circuit that makes a sound louder or distorted if you’re thinking of a guitar, but the Amplifier section here is just used to control the volume of the sound through a knob. Without further knowledge, we can build our first synth out of these modules. A very simple synth we can build is made of three components: an Oscillator, an Amplifier (AMP), and a keyboard to trigger the notes. When we turn on our synth, we hear an infinitely continuous sound generated by our oscillator(s).
What does this minimal synth design allow us to do up to now?
- We can change the pitch (frequency) of the notes through the keyboard (by pressing different notes).
- We can also control the volume of the sound coming from the oscillator through the amplifier’s volume knob. Setting the amplifier knob to 0 would obviously result in no sound (volume 0) while higher values will lead to an increase in volume.
- Limitation #1: every time we hit a key on our keyboard we hear a sound right away. The sound continues as we keep holding the key. Not very practical to use as you might guess, but starting with this simple synth design will help us understand the nature of each module as we add them to our minimal synth design.
- Limitation #2: We can definitely make a sound using our simple synth, but you will notice that the sound we get fills the entire frequency range of the spectrum from the lowest frequencies (0 Hz) to the highest ones (20,000 Hz or 20 kHz) (see figure 1.2.1).
SPAN Spectrum Analyzer by Voxengo
3. SOUND DESIGN MODULE #3: VCFIt might be okay to play with a sound occupying the whole frequency spectrum (0Hz to 20kHz) on your synth, but you will encounter clashing and masking issues as soon as you add a second sound to play along the first one like a second synth. Both synth frequencies will fight and we will lack clarity and definition in the resulting sound. To overcome this situation, we can remove unwanted frequencies from our initial synth sound so that the overall mix sounds cleaner, and more polished. To do this, we add a third module to our synth called the VCF (Voltage Controlled Filter). The VCF is basically a filter that lets you remove frequencies you don’t need. So instead of having your sound playing on all frequencies (0 Hz to 20 KHz), we will filter it so it plays on frequencies from let’s say 0 Hz to 1000 Hz, thus getting rid of higher frequencies (above 1000 Hz). For example, if you want to create a bass sound, you may want to eliminate high frequencies above 1000 Hz. See the figure below:
Spectrum showing frequencies from 0 to 1000 HzPro Tip: Mixing starts at sound design. Manipulating a sound at its source to fit your track is way more effective, musical, and natural than trying to adjust it at the mixing stage. This is the most obvious and fun section to play with on a synth as you clearly notice changes in the sound. The filter section (VCF) is composed of three parameters:
- The Cutoff frequency
- The Resonance
- The Slope
The Cutoff frequency
High Resonance (Q)
Low Resonance (Q)
Selecting a slope of 12 db/octave means our sound is attenuated by 12 db for each octave up. Meaning the sound gets attenuated by 12db at 500 Hz, then by 24db at 1000 Hz, then by 36 db at 2000 Hz, and so on… Now, let’s continue with the same example, but we will select a slope of 24db/octave (instead of 12db/octave). Our sound will get attenuated by 24db per octave after the Cutoff frequency of 500 Hz. Meaning at 500 Hz, the sound is attenuated by 24db, then by 48db at 1000 Hz, then by 72db at 2000 Hz, and so on… As you can see, the 12db/octave slope is more gentle and musical as it attenuates the frequencies smoothly. On the other hand, the 24 db/octave slope is more aggressive and can be used to sharply remove unwanted frequencies. For example, many mixing engineers remove the frequencies above 10 KHz with a 24db/octave slope to get rid of a hiss in a guitar. Note: an octave higher represents the double of the frequency of the base octave. For example, the frequency of C5 (C in the 5th octave) is 523 Hz. The next octave is C6 (C in the 6th octave) and its frequency is 1046 Hz.
ADDITIONAL TYPES OF FILTERSIn the previous sections, we discussed only one type of filter which is the Low Pass Filter (LPF). There are still two additional types of filters you can find in many synths: The High Pass filter (HPF) and the Band Pass filter (BPF)
- HPF (High Pass Filter): does the opposite of the LP filter. It gets rid of the low frequencies letting the highs only pass. Very helpful in situations where you want to filter the low end part of a sound to leave some room for your kick and bass.
- BP (Band Pass Filter): it gets rid of both high and low frequencies. This is similar as combining an LPF and an HPF together.
4. SOUND DESIGN MODULE #4: ENVELOPESEvery time we trigger a key on the keyboard, we hear the oscillator generating a sound that starts as soon as we hit the key and stops directly when we release it. That’s ok, but if you want to make a track, you will quickly notice how inconvenient it is to have the same sound contours over and over. It is like you want to decorate a house and the only thing you put is a square block of concrete that takes up too much space in your living room. You might want to sculpt this concrete block to make a nice and pretty statue out of it. The statue will be sculpted according to the room where it exists to perfectly fit the space. Well that works exactly the same in sound. Oscillators generate a raw sound (your block of concrete) and your envelopes help you sculpt it to fit your track (room). The parameters of an Envelope are: Attack, Decay, Sustain, Release (ADSR):
- Attack: The time (in ms) it takes the sound to fade in starting when the key is pressed.
- Decay: The time (in ms) it takes the sound to go from the Attack to the Sustain level
- Sustain: the level (in db) or amplitude of the sound when you hold a key.
- Release: The time (in ms) it takes your sound to fade out after you release the key on your keyboard.
5. SOUND DESIGN MODULE #5: LFOMany sound design amateurs get trouble in this section as they don’t understand it very well. The truth is if you understand the basic function of the Enveloppe module then it should be easy as a breeze to understand the LFO section. The LFO (Low Frequency Oscillator) section lets you simply automate the movement of any knob in your synthesizer. Let’s say we want to open the filter cutoff and close it repeatedly at a specific speed to have a wobble effect. You can do it manually with your hand, but this is not a really elegant way of doing it, plus you might not get precise results and your hand might be too busy preventing you from performing or adjusting other parameters. You can use an enveloppe and assign its destination to the filter cutoff. However, the filter cutoff will open and close only once (one-shot) each time your trig a key on your keyboard. Remember, we are trying to repeat this movement infinitely and not only once every key hit. That’s where LFOs come handy… What we can do is assign the filter cutoff to our LFO destination so the filter can open and close at a steady speed (also called rate). The LFO (Low frequency Oscillator) has three main parameters: Source, Destination, Speed
- Sine waveform
- Triangle waveform
- Sawtooth waveform
- Square waveform
- Random waveform
The Speed (also called Rate):
LFO destination examples:Alright, that’s a lot of information here! Let’s look at some examples to make sure you understand what an LFO does.
- AM: Amplitude modulation is very simple yet extremely powerful. AM simply means the volume of the synth is being modulated up and down.
- FM: Assigning the oscillator frequency (pitch) as a destination results in FM (or frequency modulation).
- Ring Modulation: If you have at least two oscillators in your synth, then you can select oscillator 2 frequency as your LFO destination. Make sure your LFO amount is not at 0 (so you can hear the modulation). What happens here is that your oscillator 2 frequency (pitch) keeps changing while the frequency (pitch) of oscillator 1 remains static resulting in incredibly rich, evolving, and complex textures coming out of your synth.