K403/K503 Assignment 8: Introduction to Absynth

Absynth is a software synthesizer for the Mac and PC. We'll use it partly to reinforce classic analog synthesis concepts, which will appear on your final exam.

The goal of this assignment is two-fold:

  1. to figure out how to run Absynth and make noise with it; and
  2. to learn about basic synthesis patches and waveform properties.

Since your Final Project is due very soon, you should spend only a little time on this assignment. The Final Project is much more important. You might want to revisit this assignment while studying for the exam.

Playing Absynth

Here's how to run Absynth and play it with the PC88 keyboard.

  1. Launch Absynth. If it's not in your Dock, find it in /Applications.
  2. Make sure the audio and MIDI settings are right.
  3. Now whenever you play notes on the PC88, you should see those notes light up on the Absynth keyboard. (If you don't see this keyboard, click the little keyboard icon at the right of the window.)
  4. You should also hear sound from Absynth when you play notes. Turn up the 828 Main Out channel faders on the mixer, and make sure other input sources are turned down.

    Play around with the preset sounds. To choose these, click the Browser button. You should see a File Browser list on the left. (If you don't, click the Sounds button above the list.) Double-click on the "Absynth 4" folder to reveal the "Effects" and "Instruments" folders. Click on the "Instruments" folder: a list of patches appears to the right ("A Beautiful Place," "A Dark Place," etc.). To use a patch, double-click its name.

Basic Patch Creation

Explore the basic synthesis patch discussed on the handout you were given in class.

  1. Choose File > New Sound. You get a simple sine wave patch.

    Do not start editing one of the existing factory patches. It's better to start from scratch when learning Absynth programming. Once you understand how everything works, it's very instructive to analyze the factory patches.

  2. Click the Patch button to see the architecture of the patch. A patch comprises several different modules, or units that perform a particular function, such as oscillators and filters. You can enable and disable modules by clicking on their left borders. The signal flow between modules should be apparent.

    There are three independent oscillator "channels," arranged in columns (A, B, and C). The top module in any column is the oscillator (like the VCO in an analog synthesizer); the module below that is the filter (like the VCF); the module below that is a ring modulator (called "Mod").

    So where is the VCA? It's not a module, per se. Instead, you have control of the amplitude of each channel, using the slider just below the ring modulator. (This is the offset, or initial setting, of the "VCA.") Also, you can control the VCA from an envelope generator or LFO.

    After the three channels are summed, the signal can go into a chain of different kinds of effect: a waveshaper, a filter, and a delay-based effects processor.

    Absynth oscillators run in one of several modes: Single, Double, FM, Ringmod, Fractalize, Sample, Granular and Audio In. All but the last three function as wavetable oscillators. The wavetable stores a single cycle of a waveform, and the oscillator plays that waveform repeatedly to make a boring steady-state sound at whatever pitch you request. (Different pitches are made by skipping samples in the wavetable, which makes a higher frequency, or by interpolating between existing samples, which makes a lower frequency.) Often several oscillators go together to make up a single oscillator module. For example, in Double mode, there are two independent oscillators per module.

    The challenge in wavetable synthesis is doing things to make the inherently static oscillator sound change over time. There are many ways to do this, such as using envelopes, LFOs and MIDI continuous control to alter the synthesis parameters. As you follow the tutorials and work with your own patches, always ask yourself what you can do to make the sound change over time.

    In Sample and Granular modes, the oscillator plays from a sound file you specify, rather than from a single-cycle wavetable. With Audio In mode, you can route live audio from outside the program into its various modules.

  3. Absynth provides an editor for the waveform used by oscillators. Click on the waveform popup menu in the first oscillator module, circled in red below.

    Click the New button. The waveform editor opens, showing one cycle of a sine wave.

    Use the three drawing tools (click to right of "Draw Mode") to reshape the waveform. Play notes to hear what happens. Notice that the more jagged the waveform is, the brighter and nastier it sounds. Use the dB and Offset controls to see what they do. Does changing the offset change the sound?

  4. Go nuts clicking with the straight line tool to make the waveform really jagged. Listen. Now choose Filter from the Transform popup menu. The Filter Waveform window appears. Using one of the lowpass filters available in the filter popup menu, lower the cutoff frequency. Notice that the waveform becomes smoother as you roll off the higher frequencies. Click OK to return to the Waveforms window.
  5. If you want, play around with the Fractalize command in the Transform popup menu. Most of the other commands are interesting, too.
  6. Click on the Spectrum button: now the window shows a graph of the waveform's spectrum. Each vertical bar controls a harmonic partial. The yellow bar sets the amplitude of that partial; the blue bar sets its phase. From the Transform popup, choose Load, and select Sine. Notice that there's only one harmonic, with phase at zero. If you were very patient, you could construct a triangle, sawtooth or square wave by clicking on the appropriate yellow bars to set the amplitudes of harmonics, using the formulas on our waveform handout (1, 1/2, 1/3, 1/4, 1/5, 1/6, etc. for a sawtooth wave). Then you would click on the Waveform button to see the time-domain representation of the waveform.
  7. Leave the waveform set to something that sounds buzzy (like "Saw_real," then return to the Patch window. Enable the filter module below the active oscillator, and try the different filter types. Use the Hz control to set the cutoff (or center) frequency. The other controls set resonance, Q, bandwidth, gain, etc., as appropriate to the filter type. You'll probably get the most dramatic effects with LPF -24 dB (lowpass filter with steep 24 dB per octave cutoff), which also has a resonant peak that you can control. But remember, you have to have a bright waveform with lots of frequencies before the filter will do much. A sine wave won't work.
  8. The LFO and Envelope windows are beyond the scope of this short exercise, but feel free to play with them. We'll cover these in some depth next semester. The idea is that you have three LFOs that you can use to modulate the pitch of any of the oscillators, the cutoff frequency of any of the filters, the amplitude of a channel, among other things. You can make envelopes control many of the same parameters. The envelopes are very flexible, containing many segments and allowing for looping.
  9. Save your patch by clicking the Save button near the top of the window. Open the patch file later with File > Open Sound.

Controlling Absynth from Digital Performer

You can set up Absynth so that it can be controlled by a MIDI track playing in Digital Performer. Also, you can route Absynth's output into a Digital Performer audio track, to which you can then apply audio effects.

If you're interested in trying this, here are some hints...

  1. In Digital Performer, create a virtual instrument track (Project > Add Track > Instrument Track > Native Instruments: Absynth 2).

  2. Absynth now should appear as a MIDI device (i.e., in the Output column popup menu for MIDI tracks), just as the K2600 does.

  3. Record-enable this MIDI track in order to play Absynth from the PC88.

©2008, John Gibson