Points of Interest

Synth sounds would be too static (and thus boring) if there were no modulators like envelopes. To get even more spice into a sound, synth programmers use low frequency oscillators, in short LFOs.

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While the lowpass filters are the most important in synthesizers, highpass, bandpass and bandreject (aka notch) filters are nice to use as well. Here are some examples. The horizontal red bars stand for the partial tones in a waveform. The gray area emphasizes the partials that are allowed to pass the filter. The light red bars show the partials being filtered out.

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I’ve posted about ADSR envelopes earlier. You will find them in most synths. However, some synths provide further waveforms. As a monophonic solo synthesizer, the Minimoog provided no release portion. This results in a simpler ADS envelope:

ADS Envelope

Here’s a live video of the WDR, where Klaus Schluze is treating his various synths back in 1977.

And here’s one more remarkable video, where Józef Skrzek plays a pipe organ and a Minimoog simultaneously. It’s stunning what the Moog sounds like.

ADSR-Envelope

One of the most essential modulators found in synthesizers are envelopes. Most synths at least provide two envelopes – one for the amplifier, one for the filter. Both allow to apply a contour to the sound, the first one to the volume, the latter one to the spectrum of partials.

The most basic type of an envelope is the ADSR envelope. The four characters stand for Attack time, Decay time, Sustain level and Release time. The above figure should give you a glue what this is all about. The envelope gets triggered as soon a key is pressed. After that, it raises to the maximum level, and falls down in the decay time until it reaches the sustain level. This level gets held until you release the key. After releasing the key, the envelope falls down to zero during release time.

For solo sounds, both the attack and release times usually are set to small values, so the musician only needs to adjust the decay time and sustain level to his likings. You can hear an ADSR envelope applied to a lowpass filter on the previous post.

Sieves, AD 1568 (wikimedia commons, public domain)

I’ve posted about base synthesizer waveforms yesterday. The signal from the oszillator(s) most often gets used to feed a filter. Almost all synths at least provide a lowpass filter. Some synths provide a multimode filter, which may contain lowpass filters in different characteristics, a highpass filter, a bandpass filter, a notch filter and maybe a comb filter. Those filters are not static. Instead one can change the cutoff frequency of the filter, which effectively means that the range of filtered partials can be influenced.
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Most synthesizers follow a similar approach. There’s one (most often two or three) oscillators which generate the base sound. This sound then passes a filter to filter out the unwanted harmonics. Finally, the sound gets out of the synth and is fed into an amplifier and the speakers.

Actually, it’s much more complex, but basically, that’s it. Most synthesizers provide at least the following four base waveforms:

A sinewave

A sinewave

A triangular waveform

A triangular waveform

A pulsewave

A pulsewave

A sawtooth wave

A sawtooth waveform

The sinewave is a waveform which contains no partial tones at all, thus being a “boring” waveform. It is more or less senseless to filter it, as there are no partials to filter out.

The triangle wave is very similar to the sine wave, providing a couple of partials only. You can filter it, but there will be no dramatic changes in the sound.

A square wave contains all odd partials, and the sawtooth contains all partial tones. The latter two can be filtered to achieve sound changes. Sine and triangle waves are mainly used to phatten the sound or to do some interesting modulations.

Square waves often can be modulated to change their pulse width while the sound is being played. I’ll post about it in a later issue.

Because the oscillators provide the base audio material, the synth manufacturers care a lot about the “right” waveforms. Thus the waveforms slightly differ from synth to synth. The above examples have been recorded using a Korg Z1 synthesizer, which gave me the “nicest” oscillator images. On other synths, like the Waldorf microQ, the waveforms have less sharp edges, resulting in a different sound base.

Oscillators can have much more features like additional waveforms, samples, sync, frequency and cross modulation or additive synthesis. But anyway, many sounds are just built using a sawtooth or a pulsewave. If you plan to learn how to program synths, remember what they sound like.

Eigenlabs offers a completely new electronic instrument, the Eigenharp. For me as a synth addict, it looks like a very interesting instrument. Obviously I’m not talking about the price, but about the musical expressiveness and flexibility. The Wikipedia article still is a stub, but links to a further video.

Yes, I’d like to try it out immediately, but it seems it has not arrived at the german shores yet. Maybe the Pico is worth being an Xmas gift :) .

Update:

The inventor provides more detailed information in a video shared by Engadget.