Sound Synthesis 101

By now you have seen quite a few virtual synthesizers with a bewildering array of GUIs. In this section, we will try to see what they all have in common with the goal of being able to modify and create patches.

In the most general terms, a synthesizer is an electronic instrument that sends one or more pure waveforms through a pipeline of filters and other processors to modify and mangle that waveform. The classic starting points are the sine, the square, the sawtooth, and noise. Pulse and triangle are also fairly common. Some hybrid waveforms are not unusual, and as we saw in Zebralette, some instruments let you draw and stack waves to produce very rich sounds. These geometric names are derived from how the sounds appear on an oscilloscope, which shows voltage over time, allowing analysis of things like frequency and amplitude of a signal. The pure tone is a single frequency sine wave (note that the other wave shapes can be constructed from sine and cosine waves). In theory, by crafting sounds the right way, it should be possible to recreate sounds of real instruments and nature. In practice, with a few exceptions, analog synthesizers can only approximate "real" instruments. Highly convincing, realistic patches were brought about in the 1980's by sampling synthesizers, which could be argued as cheating, since a sample, as we've seen, is just a little digital recording (and having a precise clarinet sound only showed how the keyboard could not convey all the subtleties of the human mouth tooting on a slobbery reed). In any case, it helps to listen to the unmodified waveforms to get a feeling for the starting point - many plugins have a plain vanilla initial patch that is a pure tone. A sine wave sounds like whistling or blowing across the top of a bottle, a sawtooth wave sounds a bit like it looks - like a buzzer. White noise is static and can be used for sound effects like wind or ocean waves and percussion sounds.

The short explanation for a 1970's analog synth's inability to recreate natural sounds is that those sounds are composed of many overlapping waves, not just one or two. The long answer involves complex Fourier analysis of sound waves. But synthesizers opened up a whole new world of strange and novel sounds that gave birth to electronic music as we know it today (with proper credit to early studio pioneers who were happily making what can only be called electronic music well before the invention of the modular synthesizer).

The timbre of a patch is comprised of its spectra (those waveforms) and its envelope (fast or slow attack, ringing or abrupt ending (decay), etc - drum hit versus a bell versus a slow violin crescendo). So creating your own sound is just a question of figuring out how to mess around with those two elements of timbre on any given synthesizer. A perfectly valid approach to this is to stop here, and just start "knob twisting" at random, hitting "save" when you get a pleasing result. You will soon learn what "LFO" does, even if you don't know that it means "Low Frequency Oscillator" - and after all, does knowing what the initials stand for help much?

Here are ten quick ways to modify the basic waveforms on any synthesizer. These won't make you an expert sound designer, but hopefully will de-mystify all those crazy knobs and initials. Not every synth has all of these capabilities.

Knob acronyms VCO

• voltage controlled oscillator: created the raw waveform, so this is our starting point.

LFO

• low frequency oscillator: add tremolo or vibrato.

VCF

• voltage controlled filter: add sweeping wah effects.

VCA

• voltage controlled amplifier: gain (note - this is probably post-ADSR section)

HPF

• high pass filter: knocks out low frequencies

Ten things to try on any synthesizer

1. Go straight to the cutoff filter or VCF to smooth out the sound. This is kind of skipping some steps, but it's one of the most noticeable things you can do to affect the sound on any synth. You'll notice that slowly modifying the cutoff frequency makes the classic "sweep" sound, and it should be possible to use another control, such as the LFO, to automate that sweeping as the note is held down. Early modular synthesizers allowed you to connect anything to anything and see what happens. In the same spirit, most plugins have a way to route a controlling signal from here to an oscillator over there. Take a moment to look at the panel and break down the various sections and the signal flow.
2. The most understandable and quickest way to modify a sound is to play with the envelope, which will be labeled "ADSR" for "Attack, Decay, Sustain, Release". Let's say you pluck a guitar string. The attack is the ramp up, which is pretty abrupt, the decay is the other side of that initial pluck - the time it takes to reach the sustain time (the remaining time the note remains level). The release is what happens when you let go (or lift your finger from the key). In the case of a real guitar, the sustain would be about three or four seconds and the release would be around zero. It's fun to give a sound a very long release so you can just tap a key and listen to it slowly fade. Some sounds lend themselves to a gradual attack, although if it's too slow, it may feel out of tempo in the context of a particular recording. Smaller changes to the attack come closer to emulating real-world differences which are in the millisecond range. A snare hit is instantaneous, a tuba or french horn is less precise, and the sound of a gong may peak well after it is struck. Organ notes play at one volume and stop the second you release the key. All of these aspects to sound are governed by the ADSR section, and changes to the sound from the other sections generally happen over time, so the ADSR is indirectly affecting those, too. Note that some plugins will also have a "hold" (H) parameter that may be used to set a fixed duration for sustain or the full volume of the attack, ans have "ADSHR" or "AHDSR" sections.
3. Try creating a cymbal crash by using only white noise, then tweaking the ADSR. What happens when you make that cymbal a very short blip?
4. Another instant alteration of a waveform is ring modulation, if it's available. This gives a harsh bite to your sound, almost the equivalent of adding overdrive and a little distortion to an electric guitar (those sorts of patches very likely use ring mod or resonance). Usually you only need to enable it, but try tweaking it to be more or less subtle.
5. Just jumping the octave can alter a patch in unexpected ways. Does that "Killer Bass" also work as a lead patch when played in a higher register? What if you knock it upstairs then tweak the envelope a little? Many synths have a button to transpose an octave at a time (and another way to change properties of a note, including pitch).
6. Try the LFO to chop up a sound or add wobble to a sound.
7. Portamento, anyone? This is another parameter where a little goes a long way. Overdo it and you're left with a cartoony slide whistle that is only any good for a special effect. But adding just a touch can juice up a lead sound nicely. You'll notice a fair number of presets use it that way.
8. If there is an effects panel, slapping on some delay can high a high impact. Put another way, I have noticed removing the delay from certain rompler (sample-based plugin) patches (I won't name names) reveals the underlying sound to be less than inspiring. Re-enable the delay and it's ready to go to Mars.
9. Many synths have multiple oscillators. A quick way to get a more sophisticated sound is to detune one or more waves just a tiny bit. So look out for a knob that says "detune". That is a quick way to get a fat, hovering sound.
10. One last section that is not on nearly enough synthesizers is the arpeggiator. This will automatically play notes you hold down, and often you can choose in what sequence - up and down, only up, only down, random, or in the order in which you play them. This classic synth trick can be the basis for a whole song!

So far, this discussion has focused on analog synths because a lot of free VSTs are analog emulators. There are many different approaches to sound synthesis, and the description for each plugin will say which type of synthesis it is are using. Some instruments purposely take a radically different approach to either the interface or to sound generation or both. For me, the more quirky and experimental, the better. But occasionally, a plugin is just impenetrable. In that case, just go with the presets or move on. You should not have to battle a synth just to tweak a patch. On the other hand, it is only fair to read the manual. I mostly stick with presets, but still feel a passing familiarity with the history of how synthesizers have evolved, the lingo, and the capabilities is important - a short list of resources appears in the appendix. Go forth and knob-twist!

Approaches to Sound Synthesis

Here are very brief descriptions of some of the major types of synthesizers that you will see recreated as plugins. Between other methods not mentioned and hybrids, this is just scratching the surface.

Subtractive

• Applies filters to complex waveforms. Can employ Pulse Width Modulation, which sounds like a chorus or detuning effect.

Formant

• A subset of the subtractive approach that pays attention to the formant or characteristic frequency peaks associated with the resonant cavity of the instrument being modeled.

Modular

• Early 1960's synthesizers such as the Moog and Buchla were massive component racks; individual components were connected by patch cords. These analog synthesizers were bulky and expensive. In recent years, there has been a resurgence of interest in modular synthesis, and there are emulators that let you draw a "cable" between inputs. It's still expensive to build a "eurorack", so a plugin is a great way to test the waters, if you aren't sure it's for you.

Additive

• Adding waveforms results in more harmonic overtones - the components of natural sounds mentioned before.

Frequency Modulation (FM)

• Through multiple oscillators and a more graduated voltage control scheme, digital synthesizers like the Yamaha DX7 (1983-1989) offered sophisticated sounds at an affordable price.

Wavetable

• Uses random waveforms as the tone generator.

Phase distortion

• Starts with more complex digital waveforms In the Casio CZ series, which also emerged in the 80's, the digital filtering and amplification also went through an eight stage envelope, allowing for sounds that evolved over time more than could be achieved with the usual ADSR.

Physical modeling

• Ever greater processing power allowed for mathematically modeling not only the detailed harmonics of an instrument, but other parameters such as the resonance of the body.

Sampling

• As we've seen, samplers are digital recordings of individual notes that can be played back at different pitches. ROMplers are plugins that rely on sample presets - both keyboards and plugins can apply additional filters and effects to samples, layer them, etc.

Granular

• A sample is chopped into millisecond bits which can then be layered, played back at different speeds, and processed.

Patch Tutorials - Funk Bass

Let's apply some of the above ideas to make a simple funky bass, a classic analog synth sound. This need not be polyphonic, and it will have a very short, almost clipped envelope. It needs to be thick and needs to go "BOW-BOW-BOW", which effect will be achieved with a filter. We'll use the highly-rated Synth1, modeled after the Nord Lead Red. Download it to your VST directory from here (note 32 bit versions often work better than 64 bit):

http://www.vst4free.com/free_vst.php?plugin=Synth1&id=245

Start Synth1

1. Open the terminal window and change directory to where you installed Carla, for example:

   $ cd /usr/local/share/Carla

2. Launch Carla:

   /usr/local/share/carla$ Carla

3. In Carla's window, click the green '+' sign (Add Plugin), and select Synth1.
4. Click the gear icon on the Synth1 rack unit. You should see the GUI.
5. At the bottom of the GUI, click soundbank. A popup window will appear. Select the "All" dropdown menu and navigate to 01:soundbank01(0) - this is a completely empty soundbank.
6. Load the first sound by selecting it, then close the soundbank window.
7. Now set the parameters to match the following screenshot.

Notes on the Funk Bass setup:

1. In the far right panel, disable any effects by clicking the "ON" button until it goes gray.
2. To get the clipped envelope we're after, turn everything down on the ADSR control but the decay.
3. Choose the sine wave for oscillator 1.
4. Now just tweak the filter settings in the middle of Synth1's middle panel until you get somehting you like. For more wah, open the attack filter.
5. You can go back to Oscillator 1 and try different waveforms. Recall that sawtooth has more "bite"? Now you can hear that for yourself. Play with other parameters one at a time to see what effect they have on your patch.
6. If you like this patch, use the dark red "write" button at the middle bottom of the GUI. A popup will let you name the patch and save it to the empty bank for your next session.

Arpeggiator

To try out tip #10 above, download Poly 2106, a well-executed Juno 106 emulator, from here: http://www.vst4free.com/free_vst.php?plugin=Poly_2106&id=1329

This plugin has very clearly marked "Arpegiator [sic] Gate" section at bottom right. Just click the "OFF" button so it changes to "ON" and turns red. Then play around with the controls in that section. Note that "HOLD" will keep the pattern playing even after you release the keys. Experiment with the other controls to vary the tempo and direction of the arpeggio. TR-GT mode lets you space chordal hits on a timeline, and they can be more or less legato.

Crafting Noise

Install TAL-Noisemaker from here: https://tal-software.com/products/tal-noisemaker

The following setup modifies a noise signal. The envelope is set something like a crash cymbal, but instead of a static filter setting, LFO1 and LFO2 are controlling the filter. Adjust the rate on the LFOs to your liking, or click the dropdown that says "Filter" to disable them. Note that Master/Sub is turned all the way down.

Disabling LFO1 and 2, slightly raising the Cutoff and Resonance, and shortening the envelope turns our wavy crash cymbal into something more akin to a hand-clap.

And what discussion of noise patches would be complete without the Helicopter sound effect? This one fades into the distance when you release the key.

Minor modifications to the envelope and other controls can change plain noise into different percussion sounds or sound effects.

Siren

Here is an example of controlling the pitch of an oscillator with the LFO. Install Pure Pone from here: http://www.vst4free.com/free_vst.php?plugin=Pure-Pone&id=877

Certainly not the most musical setting, but a good demonstration of how to modify a parameter from another parameter, the essence of synthesizer programming.

1. Call up the patch called Analog 6 (because it is a relatively plain vanilla patch).
2. Turn off Modulation Bus 2, we don't need it.
3. Set Modulation Bus 1 source to LFO, it's destination to OSZ1-3, and the amount to MOUNT.
4. Crank up the Amount to about 6.
5. I set the LFO to use a Sine wave and the rate of this oscillator to about 3.
6. After playing around with the Oscillators, it sounds best with OSZ1 turned off, so toggle that switch.
7. Set the waveform for OSZ2 to triangle a sawtooth and octave to 0.
8. Set the waveform for OSZ3 to the triangle in the opposite direction of OSZ2's, and octave to 1.
9. Make sure any effects are disabled.

You should hear a slow rising and falling pitch.

• • To make it go faster, increase the LFO frequency.
  • To make it see-saw like a European police siren, change the LFO waveform to a square wave.
  • To change the pitch range, adjust Mod Bus 1's Amount.
  • Hear what happens to the timbre as you modify the waveforms of OSZ2 and 3.

I had a little trouble finding a plugin where it was simple to make the Siren patch, but I hope these examples were enough to illustrate that there is a lot in common from one plugin to the next in editing and creating patches. One or more sources (oscillators) is modified by various signal processors and effects, some of which may themselves be waves, some will be filters. Once the wave is shaped, it goes through the ADSR envelope, the the master volume control. Usually, these controls are in some kind of sectional arrangement. It just becomes a question of figuring out how to assign them. With a little practice, you will be able to imagine a sound and have a rough idea of how to build that patch from scratch. While there is nothing wrong with using presets, as you can see, a tiny twist of a single knob can dramatically alter what you get from a given patch. Presets are intended to demonstrate the capabilities of a plugin, so don't be afraid to mess around with the controls. Any synth developer would tell you "that's what they're there for!"

The opening preset of Osiris-6, "Delay Pad" is a perfect example of a sweep effect with a slow attack.

Osiris packs a lot of sound editing capability into a relatively easy-to-follow layout. Two oscillators are on the left. The yellow buttons rotate through all available options. You can pick filter 1, 2, or both. And the panel outline suggests that the filters have their own ADSR, which is above the ADSR for the gain. To the left of the keyboard is the mono on/off and portamento control. Tucked to the right of the keyboard is the arpeggiator. Effects are front and center. It is very easy to page through the options for LFO1 and LFO2 as you listen to how the sound is affected in real time. This is truly one of the best designed front panel layouts. Osiris shines in the pad department, but the cutoff and resonance knobs do not seem to alter those sorts of sounds much. One drawback of this plugin is that it appears to take up a lot of memory - it failed to load four times on my old laptop. Download it here: http://www.vst4free.com/free_vst.php?plugin=Osiris-6&id=741