In this tutorials we are going to deal with what is probably the most important aspect of shaping any given sound, the ADSR, and I believe you now want to know what that means? But before we get onto this crucial topic we need to understand another component of sound and that is Volume or Loudness and how it is measured. We discussed Amplitude in Part1 but I deliberately left out the measurement scale dB, so that we could apply it later when we come to cover synthesis in more detail. For now, here is a simple explanation.
dB: deciBel . The level of a sound or volume is measured using the dB scale. Deci being a tenth and Bel being the unit. A deep and moving question at this point is: ‘Why do we measure in tenths and not in single units?’ And the equally moving answer is: Our ears can hear a vast number of audio levels and it would be a mathematical nightmare to try to use the ‘actual’ numerical representations of audio levels, so we use tenths to make it easy to understand and calculate. I am sure you have seen this on your mixer, on software editors, on DAT players, just about everywhere in the audio industry. In the next tutorial it will become clear why we need to know this.
But for now………
A : attack
D : decay
S : sustain
R : release
These are the components of the envelope of a waveform.
Envelope: generally this is the term used for the rise and fall in volume of a single note over time. Think of it in terms of the shape of a sound and you will have a better and clearer concept of what an envelope is. This shape determines what the note or waveform will sound like and the above ADSR are the components that make up that shape. Of course I am being very simplistic here but I want you use the tagging and visualising techniques we used in Part1. I would also like to point out at this point that envelopes are also used for many other areas of synthesis but for this example we are looking at the amplitude envelope, volume over time.
The best way, as always, is to show you graphically how the ADSR of an instrument looks and behaves. Fig 1 shows a standard ADSR envelope.
So, as you can see from my outstanding diagram that the note starts at zero, has a quick attack and rises to it’s highest value, then has a small fast decay ( quick drop) down to about half way of the volume of the note, then stays there (sustain) for some time then has a short smooth release.
As you can imagine, a pad sound would have a very long attack followed by a slow decay then a long sustain and a very long release. This will give you that smooth, slow build and nice tailing off.
An acoustic bass will have a quick attack for the plucked effect, with a short decay, where the plucked sound drops to the sustained section which will be constant as it is the body of the sound, and then a short release as acoustic basses are ‘fingered’ and to get that ‘let go’ effect the release needs to be relatively quick. But on some acoustic basses the release can be longer to give that ‘let go’ effect that stays around and decreases in volume slowly.
For synthesizer type of basses the attack is either quick, if snappy, or slightly slower when dealing with the more throbbing type of bass sound that builds over time, the decay will be short but slow and the sustain will be lengthy and close to the maximum peak of the attack, the release will be either fast or slow depending on the type of sound chosen and whether the user wants to be able to ‘roll’ from one note into another without cutting out.
A drum sound, in fact most percussive sounds, will have a quick attack followed by a short decay, very small sustain and an immediate release, easily recognisable.
Other ways of manipulating sounds by adjusting the ADSR is to take, for example, a string sound that has a slow attack, slow decay with a long sustain and long release. If you were to change the ADSR to have a quick or fast attack, a short decay, a sustain that maximises to half the volume of the envelope and a very quick release, then you have now created a stab type of effect, short notes that can sound like the string is being plucked. All you have done is adjust the ADSR.
The ADSR is critical in how a sound behaves when a note is engaged and these characteristics determine if the sound is plucked, pulled, slapped, pushed etc…These four components shape the sound and determine it’s behaviour over time.
A good way to experiment with the ADSR of any sound is to create different waveforms using any software editor or hardware sampler with a graphic or waveform display. That will familiarise you with the different types of envelopes for different sounds. I use Sound Forge and in fact most of the examples on these tutorials and screen captures (images) are all taken from Sound Forge. But use whatever means you have at your disposal for creating different waveforms and spend some time changing the attack times or lengthening the sustain points, basically alter any of the ADSR components and you can then hear the differences these changes make. Sound Forge has a nice little option whereby you can create waveforms using the FM synthesis tool. By creating a waveform you can then see the nodes for each ADSR component and you can move these around and have some fun, both visually (eyes) and aurally (ears). The screen capture below illustrates this beautifully. Those little squares you see are the ADSR nodes and by clicking and dragging those nodes you can create new envelopes. You can see how similar it is to Fig1. Now is that funky or is that funk
Okay, so now we have covered ADSR and glossed over a little about what an envelope is. As this tutorial progresses, you will see how often we use the word envelope and ADSR can also be applied to just about anything that can be manipulated. You will often see the terms filter envelope or velocity envelope etc…..You will also come across ADSR envelopes for filters on analogue synthesizers etc…
As promised in the last tutorial, here is a list of the general terms and abbreviations used in synthesis. For now, I just want you to familiarise yourself to the terminology. I do not want you to learn it parrot fashion as that will just serve to confuse you and, remember, this is a tutorial and not a test.
For this month I want you to create as many waveforms as possible and alter the ADSR of each waveform and save the results. Study the waveforms of commonly used instruments like pianos, basses, drums etc…whilst listening, and soon you will get a good idea of the ‘shapes’ of their envelopes and how they sound. Apply any ‘tagging’ method that works for you. I want you to get to the point whereby you will look at a waveform and deduce what instrument it is.
KybdTrk: keyboard tracking also known as key follow/scaling
EG: envelope generator
Sus: sustain (in synthesis , in music it means a suspended chord/note)
Lfo: low frequency oscillator
Vca: voltage controlled amplifier
Vcf: voltage controlled filter
Vco: voltage controlled oscillator
Dco: digitally controlled oscillator
Dcf: digitally controlled filter
Dca: digitally controlled amplifier
RlsVe:l release velocity
Midi: musical instrument digital interface
VolEnv: volume envelope
FilEnv: filter envelope
AuxEnv: auxiliary envelope
RTXfade: real time crossfade
KeySust: key sustain
ChrsAmt: chorus amount
AmpPan: amplifier pan
FilFreq: filter frequency
FilRes: filter resonance (note-on)
VEnvRts: velocity envelope rates
VEnvAtk: velocity envelope attack
VEnvDcy: velocity envelope decay
VEnvSus: velocity envelope sustain
VEnvRls: velocity envelope release
FEnvRts: filter envelope rates
FEnvAtk: filter envelope attack
FEnvDcy: filter envelope decay
FEnvSus: filter envelope sustain
FEnvRls: filter envelope release
FEnvTrig: filter envelope trigger
AEnvRts: auxiliary envelope rates
AEnvAtk: auxiliary envelope attack
AEnvDcy: auxiliary envelope decay
AEnvSus: auxiliary envelope sustain
AEnvRls: auxiliary envelope release
AEnvTrig: auxiliary envelope trigger
LPF: low pass filter
HPF: high pass filter
PWM: pulse width modulation
AM: amplitude modulation
FM: frequency modulation
RM: ring modulation
AS: additive synthesis
WS: wavetable synthesis
PhM: physical modelling
SS: subtractive synthesis
A/D: analogue to digital
D/A: digital to analogue
DAC: digital to analogue converter
DI: direct injection
DAW: digital audio workstation
DSP: digital signal processing
HD: hard disc
MD: mini disc
S/N: signal to noise ratio
SPL: sound pressure level
VU meter: volume unit meter
SYSEX: systems exclusive
These are the most common ones you will come across. I have also inserted some common terms for the technical side of our industry just to help you understand the terminology. Each month I will add to the terminology and abbreviations. As we move along in this tutorial, the definitions will become more detailed and the use of the above will become clearer.