Signals is a lively environment for real-time musical synthesis. It includes:
- a modular framework for digital signal processing of audio signals;
- a dataflow-oriented visual programming environment for building synthesizers and effects;
- a tracker for sequencing synthesizers and effects
The following are some of the features of Signals:
- samples and multisamples
- antialiased oscillators (with PolyBLEP/PolyBLAP)
- antialiased wavetables (bandlimited on-the-fly via inverse FFT)
- LFOs and many types of envelopes
- digital filters based on biquads and SVF
- virtual analog filters
- wave shapers (decimator, overdrive, tape/tube saturation, wavefolder, etc)
- effects (reverbs, delays, flanger, phaser, chorus, etc)
- visualizations (oscilloscope, spectrogram, spectrum analyzer, vectorscope)
- modules to mix and pan, stereo widening, compressor, limiter, EQ, etc
- internal oversampling when needed (typically in modules with nonlinearities that are more susceptible to aliasing)
- all control parameters are modulatable by design
- multiple approaches to control by modulation modules (envelopes, LFOs) or by tracker sequencing
- audio routing through buses (send effects, etc)
- portamento and legato support
- all code in pure Smalltalk, and available all the time for browsing or modification while running (lively environment)
The system is based on Smalltalk-80, specifically Cuis Smalltalk. It is multiplatform and runs with the OpenSmalltalk virtual machine.
As many systems based on Smalltalk, it comes complete with an environment for interactive programming, blurring the distinction between user and programmer (or musician and programmer in this case). It contains a complete development environment that allows you to browse classes, inspect objects, debug, and change anything 'live' while it is running.
Some free samples and multisamples are included in the data/ submodule. The multisamples are taken from public domain sound fonts.
Clone the git repo with --recurse-submodules in order to clone the data/ submodule:
git clone --recurse-submodules https://github.com/len/Signals
Then open a latest Cuis image, and load the package Tracker.pck.st. It will take one or two minutes to install some multisamples and generate some wavetables (it prints progress to the Transcript), and it will load the JetBrains monospaced font included with Cuis and set the theme to a new darker theme (you might need to close the opened windows if they don't update correctly).
Finally, open a FileList, go to Signals/data/projects/ and choose any of the examples. You can load it from the menu with 'open in tracker'. Also from the FileList you can import samples in WAV format to the sample library to make them available from the instrument editor menu.
On the screenshot above you can see an open tracker window. At the top there is the "instrument editor" that contains a patch of modules connected by wires (an instrument, or possibly an effect or other kind of audio processing patch). Each module morph contains controls (like knobs, sliders, a wave, etc) that can be changed with mouse scroll or the arrow keys (with shift pressed to do fine adjustments). The instrument editor is fully zoomable, you can zoom in/out with Cmd-mouse-scroll and pan by mouse-dragging the background. The instrument editor shows the patch for the instrument at current cursor position in the pattern editor below it; you have to move the cursor to see the different patches, or enter a new instrument number to create a new empty patch.
At the bottom left there is the "sequencer" or "arranger", that contains the list of patterns to be played. And at the bottom right the "pattern editor" that shows the current pattern and allows you to edit the triggers (notes and effect commands, like a typical tracker). Each track contains the following columns: instrument number, note, velocity, fx1 and fx2. The following are the fx commands currently implemented:
- Cxy set velocity to x (0 = 0.0, F = 1.0) after (y+1)/16th of a line
- Rxx retrigger every (xx+1)/256th of a line
- Gxx glide to note at speed xx in 1/16th of a line
- Lxx set instrument volume level to xx (00 = 0.0, FF = 1.0)
- Pxx set instrument pan (00 = left, 80 = center, FF = right)
- Ixx / Oxx adjust volume level up/down
- Jxx / Kxx adjust pan left/right
- Uxx / Dxx adjust note up/down
- +xx / -xx adjust velocity up/down
- Sxx set sample offset
- <xx / >xx set speed to xx and play backwards / forward
- 0xx to 9xx set control input (00 = 0.0, 7F = 1.0, 80 = -1.0)
- Fxx set BPM to xx
- Qxx delay trigger by xx/256th of a line
- Yxx set the probability of playing the trigger (00 = never, FF = always)
Trackers are heavily keyboard-oriented. The following hotkeys are the most commonly used (in PC, Command and Option are Control and Alt).
Pattern editor:
- Space play sequence from cursor line and loop it (don't loop with Opt), or stop if currently playing
- Enter play trigger or selection and loop it (don't loop with Opt)
- \ toggle track mute (Cmd-\ toggle track solo)
- Cmd-m toggle track mask in current sequence position
- Cmd-t insert new track after current track (Cmd-T delete current track)
- Cmd-n insert new pattern after current pattern (Cmd-N delete current pattern)
- Opt-Left/Right go to the left/right track
- Shift-Opt-Left/Right move current track to the left/right
- Opt-Up/Down go to previous/next pattern in the sequence
- Shift-Opt-Up/Down move current pattern to the previous/next position in the sequence
- ]/[ transpose trigger or selection one octave up/down
- }/{ transpose trigger or selection one semitone up/down
- Cmd-[/] change octave for entering notes with the computer keyboard
- Cmd-f set tracker BPM
- Cmd-g set tracker swing
- Cmd-l set pattern length
- Cmd-b set LPB (lines per beat)
- Cmd-r rename instrument
- Cmd-o and Cmd-s open and save a project (the whole song)
- Cmd-i and Cmd-e import and export an instrument
- Cmd-j toggle the lower pane (the pattern editor and sequencer)
- Cmd-+/- increase/decrease pattern editor font size
Instrument editor:
- Esc open menu to add new modules to the patch
- Mouse-drag panning
- Cmd-mouse-scroll zoom
- Backspace delete module or wire under the mouse
- Mouse-drag from a module output pin to another module input pin to add a wire
- ` to center and zoom the patch to make it fit the available space
You can use the computer keyboard to input notes in the tracker or trigger notes in realtime in the instrument editor while the tracker is playing. Transpose one octave up with Cmd-] and down with Cmd-[.
If you use Signals in a non-trivial part of your research please consider citing it as follows:
@manual{Signals,
key = "Signals",
author = "Luciano Notarfrancesco",
title = "{The Smalltalk Signals Project}",
year = 2025,
url = "\url{https://github.com/len/signals}",
}