ST4 – User manual

Congratulations! You are now the proud owner of the Tasty Chips Electronics ST4: a unique hybrid synthesizer / tracker.

Table of contents

Contents of the box
Powering on
Testing basic functionality
Signal path exploration
The Tracker
Instrument editor
System configuration
Module configuration
Recording and using samples
Potentiometer and slider behavior
MIDI commands
Firmware update


Only minimal prerequisites. No huge studio is required, the ST4 can be used with only simple USB/MIDI equipment. A small MIDI controller/keyboard is enough. A USB keyboard will also suffice. No external amplification is required. A headphone amplifier is built in.

To understand this manual, in terms of knowledge, you are expected to know very basic synthesis facts like what a square wave, envelope or LFO are.


Contents of the box

– External power brick: 12V DC, 2A. This adapter is suitable to the entire world (100V-240V AC) and only needs a IEC 60320-1 (C13) mains lead to match your country’s power sockets.

– ST4 unit

a) configured for desktop usage

b) configured for 19″ rack usage

– ST4 SD card, including samples and demotracks (prebuilt version only). For download: latest version of SD card: st4_sd.

Powering on

1) hook up the power brick to the 2.1 mm DC input of the ST4. This is located at the left side on the back (when looking from the front).

2) connect mains lead to the power brick

3) hook up the mains lead to mains power

4) switch on the ST4’s power.

The display should flash and a short introduction animation should commence. After the animation ends the ST4 should start up the instrument editor screen. This is mainly text stuff dealing with instrument and sample parameters. More about that later on. The 4×2 LFO channels should be visible in the lower right corner. These are squares pulsing up and down. A heart beat if you will.

NOTE: while the ST4 has a USB B input on the backside, this is only used for data and not to provide power to the unit! The ST4’s CPU and display will work when powered from USB, but MIDI and audio will be non-functional! Please always use the external power brick.


Testing basic functionality

Let’s hook up a MIDI keyboard or controller: Hook up the MIDI IN socket on the back of the ST4 to your favorite MIDI controller.. Configure your device to MIDI channel 1, 2, 3, or 4 and make it play some notes. The ST4 should register these by blinking a small square in the lower right corner of the screen (right from the LFO’s).


Basic sound waves

– connect the 6.35mm phono sockets labeled MASTER to your HIFI or FX units.


– connect headphone to the 3.5mm socket on the extreme right of the ST4.

Now once again try generating some notes with your MIDI controller device ..The ST4 should play a sawtooth with a low pass filter. Take care to turn up the volume controls (VOL1..VOL4) and filter cutoff (Cutoff1..Cutoff4). These controls are all located on the right side.

Great, it makes noise! Wiggle the cutoff, raise the main sail, motherfucker.


Now to test USB keyboard input.

Hook up your USB keyboard to the backside of the ST4. There’s only one connector on there that fits, so it shouldn’t be too hard. Supported USB keyboards are listed below. If the letter ‘U’ in the lower right stays red, that means the keyboard is not supported. If it goes black, it means it is supported. The keyboard’s LEDs should light up. Try pressing a few keys and check if the ‘U’ flashes from black to white.

Supported USB keyboards:

– Basic keyboards without hub (6 were tested). Some do require a replug.
– At least one Bluetooth keyboards with dongle was tested
– Apple A1048 keyboard with hub

Supported USB keyboard languages:

– US
– DE
– IT
– CH (Swiss German)

Try pressing F1. That should introduce you to the tracker screen.

The tracker screen
The tracker screen

NOTE: At time of writing not all Apple keyboard are not supported as they do not have very different USB hubs built-in depending on the model. The Apple A1048 does work. All PC keyboards we’ve tested work. Also Bluetooth dongles for wireless PC keyboards will work.

Press F2. This should take you back to the instrument editor.

The instrument editor.

OK, USB keyboard working. Sweet. That’s the tracker part working.

This means the basic features of the ST4 are in order and you’re ready to embark on your journey to make some tunes with this machine.

..But you’re not really reading this, are you? You’re already wiggling those knobs aren’t you. Well, once you’re done doing that, you might be interested in getting to know this thing’s signal path.



The ST4 allows the musician to directly access all four channels independently without moving through menus. While the exterior may look somewhat traditional with the typical potentiometers, small display and button/led groups, its per-track hands-on nature makes it absolutely unique.

Almost all of the ST4’s knobs and sliders are digitized. This allows for more flexibility yet while retaining the tactile and direct experience of oldschool analog synthesis. And, of course, a large part of the signal path is actually analog.

Another side of the ST4 is the tracker. Basically a multi-channel step sequencer with a huge number of pages and arrangement possibilities. Added to this disk IO to load and save songs and samples. In the true spirit of the home computer tracker it’s possible to edit note information and effects per step!

Signal path exploration

The ST4 is laid out visually from left to right. Voice and LFO generation are on the left. Central is the modulation matrix (4 tracks x [Voice, VCF, VCA]) and envelope section: ADSR sliders. On the right are the VCF and VCA controls.

But a picture says more than a thousand words..

Simplified schematic of the ST4 signal path. “Stacked” blocks indicate one unit per channel (four in total).



Basic voice generation is one waveform per track. Waves can be traditional forms like:


These are the 5 basic waveforms of the ST4. The voices are digital: also in saw and square mode. But these are generated using an alias-free algorithm. Voices can be detuned by using the DETUNE knobs. The top one detunes voice 1 and 2, the bottom one detunes 3 and 4. The voice with the lower number is detuned downwards, while the higher voice is detuned upwards, simultaneously. This can be used for good effect while playing chords, for instance.


The voice section also hosts 2 LFO’s, which also employ the same 5 basic waveforms. TODO: LFO section picture. Also here a single button is used to switch between waveforms. Underneath is another button named LFO RNG. This controls the speed range. Sort of like a gearbox in a car. There are 3 gears:

1) 0.2 Hz – 10 Hz

2) 10 Hz – 400 Hz

3) 400 Hz – 1000 Hz

As you can see these gears transform Low Frequency Oscillators into medium speed ones! As such they become usable in frequency modulation and ring modulation type effects. The noise waveform on the LFO can be be frequency controlled. Set it to max you get plain white noise (slightly subsampled), set to min and you get sample and hold type steps.


The bit crusher is accessed by using the BIT RES and SPL RATE knobs.  The bit crusher is easily used to turn normal samples into percussion, and percussion into instruments. A cowbell can become a distorted guitar. Low pitch sine waves become audible on laptop and phone speakers.. The bit crusher is a very powerful tool. The bit crusher is set up per instrument. More about that later.

The final part of the voice section are the two rotary encoders (endless rotating knobs) in the bottom-left.

In instrument mode (Default):

Left encoder: select instrument, Right encoder: select sample

In sample mode:

Left encoder: control sample (loop) start, Right encoder: control sample loop end

Toggling between the two modes is done with the SEL button and the mode is indicated by two LEDs.

Samples are recording by pressing REC (or by triggering over MIDI). The rec LED should start burning.

Detailed information about instruments and samples is found further on in this manual.


Directly right of the voice section you can find the modulation matrix. The matrix is used to influence the voice, VCF, and VCA of each channel. The matrix consists of 3×4 balance type knobs. These see to it that 1 LFO can be active to a separately variable degree on each unit on each channel. Keep a knob centered and it does nothing. Turn it to the extreme left and it modulates the unit by 100% with LFO1. Turn it to the extreme right and it modulates the unit by 100% with LFO2.. and everything in between (TODO: pictures).

You can, for instance, modulate VCA1 with LFO1 and VCF1 with LFO2. This may give results quite close to having LFO1+LFO2 mixed and influencing VCF1. In this way the LFO MOD matrix gives a lot of flexibility while keeping a very small footprint. LFO1 can also modulate LFO2’s frequency, which can be used for effects like a dubstep style variable speed filter sweep or for some synthetic lifeform in an alien soundscape.

The high speed LFO’s are also useful to create frequency modulation and ring modulation type effects, while having one at low frequencies can create tremolos and vibratos. These effects can be used at the same time.

Sampled LFO’s are very powerful tools, and may be used to create strange aliasing effects or very rich sounding amplitude modulation. Another application is LFO noise which is a random stepping effect: very good for frying pan and bubbling sound effects, and also for percussion.


Envelopes are of the standard ADSR type; a slider for each variable:

– attack time [0 ms .. 3.9 s]

– decay time [0 ms .. 3.9 s]

– sustain level [0..255]

– release time [0 ms .. 3.9 s]

Using sliders the envelope is easily visualized by the musician even without a display. The display adds value in that it shows the exact timing of each ADSR variable in milliseconds.

There’s a small 4×2 led button matrix underneath the sliders which let you control all channels at once, or one at a time, or even grouped. VCA and VCF may be set at the same time, or any creative combination. AUX may be used to set envelopes for bit crusher parameters, for instance.

The sliders can use “setpoint” mode, which means the envelopes you’ve just set  up are immune to mechanical glitches. When switching to another envelope the digital ADSR values will only change when you move the sliders close to them!

All envelopes can be set to looping mode.


The Voltage Controlled Filters may be set separately per channel to either:

LP (lowpass)

BP (bandpass)

HP (highpass)

..and bypass, meaning all LEDS are off and the signal completely bypasses the VCF!

Cutoff and resonance are also controllable separately per channel. See the CUTOFF and RESO knobs. Both are voltage controlled and hence can also be set via MIDI. Resonance can go up pretty high, even as high as a ear-destroying clipping self-oscillation. But this mode should be unlocked first in another menu, we don’t recommend it 😉


4 stereo VCA’s controllable by volume and panning per channel. Depending on how the VCA hardware was assembled this unit is able to add distortion, although we personally would recommend an external unit for that. The VCA hardware has mono outputs per channel and a master 2x phono output for the mixed end result (in stereo). The headphone output also reflects the master output.



The GUI consists of several screens. These are accessed by the function keys on the keyboard.

F1: tracker

The tracker screen
The tracker screen

F2: instrument editor

The instrument editor.

F3: system configuration

System configuration screen.

F4: module configuration

Module configuration screen.
Module configuration screen.

F5: mod matrix pleasantry

The LFO overview screen.

You can also scroll through the screens by pressing both encoders at the same time.


The Tracker

The tracker screen
The tracker screen

The tracker is laid out as a step sequencer as this is more intuitive to the typical synthesizer musician. However, it is a tracker because you have the option to hack in effects like volume and panning per step.

The ST4’s adaptation of the tracker is working in projects. Trackers always used so-called “modules”. A module is basically a song and instruments rolled into one. The ST4 takes this one step further and also stores MIDI keyboard configuration and all synthesizer parameters. This makes it very suitable for live usage, since your complete performance setup is now stored in a single file!

The ST4 also deviates slightly from the oldschool tracker in the sense that it has a default instrument per track instead of a global default instrument. This is more intuitive to synthesizer musicians. However, it is still possible to interleave various drum and bass instruments on a single track!

A tracker is basically a long table of notes and control changes, that plays from top to bottom. The table consists of patterns, which can be arranged how you’d like. They can be repeated at various points, or be looped. A tracker typically has the feature to enter notes with the computer keyboard. The ST4 is no different. However, MIDI IN can also be used for this.

To illustrate how a tracker song is represented in memory:

Example illustration of the ST4's song structure. Each song position can map to an arbitrary pattern.
Example illustration of the ST4’s song structure. Each song position can map to an arbitrary pattern.

As you can see subsequent positions can be used to repeat patterns, and create complex loops without copy/pasting. It also saves a lot of memory.

The special thing about the ST4 tracker is not only that it’s graphically represented as a step sequencer, but it also supports poly rhythms. In a pattern some tracks can be shorter than others. This gives complex possibilities with very little work. If that’s not good enough the LFO’s can be used to squeeze even more variation from a single pattern.

Detailed overview of the tracker screen.

The tracker is the reason the ST4 has a USB keyboard interface. The first and foremost thing are of course the arrow keys to quickly select step and track. Furthermore enter and space play and stop pattern and song, respectively.  and it makes extensive use of ctrl, shift, and alt key combos. The tracker offers inline help that comes up as soon as you press one of ctrl, shift or alt, or a combination like ctrl-shift. Each of these has a list of commands.

The first combo to press is ctrl-h. This lists a summary of the table below. To actually enter notes into a pattern, record mode must first be enabled. This is done by pressing “home”. Pressing again returns to the passive play mode.

Cut/copy/paste manipulation of patterns is done very similar to working in a spreadsheet. Shift+arrows selects text, and you can then copy and paste it to somewhere using the well-known ctrl+c, ctrl+v. The ST4 also offers underlay and overlay operations, and quick selection of columns and rows.. and last but not least exchanging blocks is also one key combo away.

Just edited some notes..
Just edited some notes..
Shift-r :select row, ctrl-c: copy
Shift-r :select row, ctrl-c: copy
Go to a suitable place to paste..
Go to a suitable place to paste..
ctrl-v: paste
ctrl-v: paste
Or choose a position in the same row, for the overlay paste function..
Or choose a position in the same row, for the overlay paste function..
ctrl+o: overlay paste
ctrl+o: overlay paste
a clean cut, the result of ctrl-x
a clean cut, the result of ctrl-x

Arranging the song is done by using pgup and pgdn in combination with shift and ctrl. The first thing to do is ctrl+pgup to increase the song length. The second thing, is to add new patterns: shift+pgup. Change your position in the song with pgdn or pgup (no shift, no ctrl).

A logical song structure would be:

pos 0: pat 0, pos 1: pat 1, pos 2: pat 2.

To do this you will need to:

1) Increase song length from 1 to 3 positions by pressing ctrl+pgup 2 times.

2) Go to position 1 by pressing pgup once.

3) Set position 1 to pattern 1 by pressing shift+pgup once.

4) Go to position 2: press pgup once.

5) Set position 2 to pattern 2 by pressing shift+pgup twice.

If you do not set the patterns, you just get a song that plays the first pattern three times.

function keycombo On-board/remark
toggle rec/play mode home
play/stop (reset step) space
play/stop (keep step) shift+space
enter shuffle ctrl+shift+’
shuffle delay up ctrl+shift+>
shuffle delay down ctrl+shift+<
tempo up “+”
tempo down “-“
select block shift+cursor keys
select row shift+r
select column shift+c
select all shift+a
transpose up ctrl+cursor up
transpose down ctrl+curor down
cut ctrl+x
copy ctrl+c
paste ctrl+v
select all ctrl+a
overlay buffer ctrl+o
underlay buffer ctrl+u
exchange buffer ctrl+e
velocity up ctrl+shift+cursor up
velocity down ctrl+shift+cursor down
panning left ctrl+shift+cursor left
panning right ctrl+shift+cursor right
octave up alt+cursor up
octave down alt+cursor down
next instrument alt+cursor right left voiceboard encoder
prev instrument alt+cursor left left voiceboard encoder
next song position pgup
prev song position pgdn
next pattern shift+pgup
prev pattern shift+pgdn
song end up ctrl+pgup
song end down ctrl+pgdn
note off Tab
delete note/command backspace
pattern break > (greater than)
load module ctrl+l
save module ctrl+s
play/stop pattern enter
switch to screen selector left enc btn + right enc btn
glide up numpad 8 per channel
glide down numpad 2 per channel
tap tempo enter (numpad)
manual panning on/off Shift+p global
half speed numpad 3 global
normal speed numpad 6 global
double speed numpad 9 global
Mute channel 1,2,3,4 ctrl+1,2,3,4
Toggle between start and loop start shift+s

Instrument editor

The instrument editor is used to edit both instruments and samples. Basically,  instrument = waveform + envelopes + fx settings. An instrument can use any of the 5 waveforms listed in the exploration chapter of this manual. It can also be assigned to one of the 8 samples in the ST4’s RAM.

The instrument editor cannot store or load instruments to/from file. In the ST4’s streamlined world, that’s what modules are for. Instead it can only load and save samples (basic 8 or 16 bit mono/stereo WAVs). However, you can copy instruments from any one of the 128 slots to any writable slot and begin editing from there.

WAV import can be done for 8,16 bit, mono or stereo types. Since the ST4’s RAM is only 512KB large, all samples are converted down to 8 bit mono. Export is also 8 bit mono WAV. Down-scaling of sample rate is not supported at the time of writing. Demonstration samples can be downloaded freely from our site in case you’re having a hard time down converting all your samples, by clicking here.

Instruments are mapped to samples like in the diagram shown below. That means that there can be multiple instruments that can have a different take on the same sample.

Instruments have an n:1 relation to samples, meaning each sample can be used by several instruments.
Instruments have an n:1 relation to samples, meaning each sample can be used by several instruments.

Conversion may be done in programs such as Audacity, but they aren’t perfect (8 bit is typically exported signed, while the WAV standard dictates unsigned!). For the best result the command line tool ‘ffmpeg’ is recommended. This gives unparalleled control! To convert an input wav to 22050 Hz and 16 bit signed, mono:

ffmpeg -i /Volumes/ST4MODULES/259309__xtrgamr__jingle-bells.wav -ar 22050 -acodec pcm_s16le -ac 1 /Volumes/ST4MODULES/bells.wav

The lowest 10 instruments are presets and cannot be edited. The GUI will notify the musician about this should he or she attempts to do so.  But of course, they can be copied to any of the other 118 instrument slots.

Most instrument parameters are accessible by pressing on-board buttons like VCF mode or Voice mode or by turning the bit crusher knobs.  However, some are only possibly by using the USB keyboard. Consider entering the instrument name, for instance.

All ST4 envelopes support looping. This may be used to simulate echoing when a note is released, for instance. Not only this, but the ST4 has 2 LFO’s per channel. LFO settings are independent from one instrument to the next. All LFO parameters may be freely used by the instrument. The same goes for modulation (even vco mod routing) and bit crusher.

function keycombo onboard comment
next instrument alt+cursor right** left voiceboard encoder instr mode
prev instrument alt+cursor left** left voiceboard encoder instr mode
next sample shift+cursor up right voiceboard encoder instr mode
prev sample shift+cursor down right voiceboard encoder instr mode
tune up +
tune down
load sample ctrl+l
save sample ctrl+s
switch loopstart mode shift+s
osc mode osc mode button (ch1)
vcf mode vcf mode button (ch1)
VCO MOD VCO MOD pot (ch1)
VCF MOD VCF MOD pot (ch1)
VCA MOD VCA MOD pot (ch1)
Loop start left voiceboard encoder sample mode, loopstart mode on
Sample start left voiceboard encoder sample mode, loopstart mode off
Loop end right voiceboard encoder sample mode
envelopes env sliders
go to screen selector left enc btn + right enc btn
toggle sample looping shift+l press right enc -> turn left enc
toggle vco env loop shift+o press right enc -> turn left enc
toggle vcf env loop shift+f press right enc -> turn left enc
toggle vca env loop shift+a press right enc -> turn left enc
enter name shift+n  –
edit vco mod dest shift+m press right enc -> turn left enc *)
edit lfo xmod shift+x press right enc -> turn left enc
toggle LFO1 sync shift+1
toggle LFO2 sync shift+2
LFO1/2 rate LFO rate pots
LFO1/2 gear LFO gear buttons
LFO1/2 mode LFO mode buttons
bitcrusher bitcrusher pots

* “VCO MOD DEST”: VCO MOD can not only influence pitch but also pulse width (PWM), and bitcrusher parameters. “PITCH “, “PWM “, “BITRESO”, “SPLRATE”

** in firmware 0.26 this was arrow up/down

Ctrl+l or Ctrl+s will take you to the sample loading menu. Here you can select a WAV from up to 100 files. You can use either the left voiceboard encoder for selecting one, or use the arrow keys on the usb keyboard.. or use numerical input to select the WAV number.

A little on how to use instruments.. It’s best to create a couple or use the presets.. Then go to the tracker screen. Now you can sequence to your heart’s desire, play your song, and tweak those pots live. Tweaking the pots here will change the sound, but will _not_ change the instruments. Only moving back to the instrument editor you can change the instrument definition. This is done intentionally, making it possible to program, sequence, and do live performance, without them biting eachother.

How to design good sounding instruments? The recipe is as follows:

1) Select a waveform or sample

2) Set the VCA envelope

3) Set the VCF mode, cutoff and envelope

4) If you think the instrument still needs more life, then start adding LFO modulation. VCA modulation is an obvious choice. VCF modulation can add that wahwah. Voice pitch modulation can add vibrato. But also PWM is possible here. Quite possibly at this point you’ll already have something decent.

5) The LFO section is quite powerful as it can also do audio rate modulation, sync, and use samples. LFO’s can be crossmodulated (option LFOXMOD). The endresult is on LFO2. You need to experiment to understand how these can benefit your music. But suffice to say they can really add a lot.

6) Need it a bit more raw? Add the bitcrusher. Remember: it’s all in the dose! This can be modulated as well. The effect is very harsh.

System Configuration

The system configuration screen is for system-wide settings. These are loaded from SD card at power on. The config file is very small and will load in a fraction of a second, not hindering startup speed. If the config file is not present, internal defaults are used.

There are several types of settings. Some are simple yes/no, others are lists, while some are scaling factors (numbers). Yes/no and list types are operated in a straightforward fashion. Left rotary selections the setting, right rotary controls the list item choice or value. If you select a numerical type, notice that you can reset/recall between 0 and a stored value, for ease of use. Pressing down the right encoder while turning speeds up the value increase/decrease.

BOOT INTRO: should a startup animation be played y/n
DEFAULT SCREEN: which screen should be started F1..F5
KEYBOARD: keyboard language (only “US” and “DE” are fully supported at time of writing)
REC/CLIP LED: the rec and clip led brightness are controlled here.
CUTOFF THRESH: cutoff [0..4000] at which resonance boosting turns to resonance dampening.

The cutoff threshold setting needs some additional explanation. The VCF can exhibit crazy self-oscillation, which is quite inaudible.. except for harsh noise lovers. This setting is intended as a safety against this. Tune it just high enough so you get good resonance, but not an explosion of self-oscillation.

Module Configuration


The ST4’s module configuration consists of an ever-growing amount of settings in ascending order of detail. Scroll through the settings with the left encoder. Select an option for the setting with the right encoder. Settings are saved within a module. You can save these settings using ctrl+s. They’re also saved automatically from the tracker screen (F1).

The configuration is very broad. Ranging from stuff like whether pot setpoints should be enabled, down to whether poly mode should be played legato or not, and even more detailed. There are several types of settings. Some are simple yes/no, others are lists, while some are scaling factors (numbers). Yes/no and list types are operated in a straightforward fashion. Left rotary selections the setting, right rotary controls the list item choice or value. If you select a numerical type, notice that you can reset/recall between 0 and a stored value, for ease of use. Pressing down the right encoder while turning speeds up the value increase/decrease.

SETPOINTS: enable potentiometer setpoints y/n. this is highly recommended. you have to slide or turn to the setpoint first before the control actually changes. setpoints are done when switching between envelopes and after loading modules..
INTERLEAVING: instrument interleaving on a tracker channel y/n. This may be news to the current day kids, but oldschool trackers allow multiple instruments on each track. For instance, interleave the bass drum with snare drum. Since instruments change LFO, MOD, ENV, and VCF parameters, this is very powerful, but may also seem daunting to beginners. Default this is off.
GLOBAL LFO: 2 the same LFO’s for all channels y/n. Easier to understand, but less powerful.
MANUAL PANNING: allows tracker panning to be overridden by manual control. useful for live performance.
POLY VCF/VCA: one channel controls all channels for VCF and VCA functionality y/n . this is effectively poly cutoff, resonance, panning, volume. overriding single channel settings.
POLY MOD: one channel controls all channels for LFO modulation functionality y/n. overrides single channel settings.
MONO LEGATO: in mono mode should envelopes be retriggered when replaying an old note y/n
POLY LEGATO: in poly mode should envelopes be retriggered when replaying old notes y/n
VCF KEYTRACK: VCF keytracking factor.. 0 (off) upto a very high number
SEND MIDI CLOCK: should the ST4 send MIDI beat clock y/n
RECV MIDI CLOCK: should the ST4 receive the MIDI beat clock y/n
FEEDTHRU CLOCK: should the ST4 feed through the received MIDI beat clock to MIDI OUT y/n
LFO1->LFO2 MOD: frequency modulation influence of LFO1 on LFO2.
POLY ASSIGNMENT: poly mode key assignment algorithm. FLEXIBLE is most used and allows you to play 3 finger chords + 1 solo key. but when you want special effects like rotating tracks, choose ROUND ROBIN.

SAVE/LOAD: select and click these to save or load settings from SD card. Keyboard shortcuts: ctrl+s and ctrl+l.

Recording and using samples

The ST4 can make extensive use of samples. Not only in its digital voices, but also in the LFO’s. Samples give the musician possibilities not easily realized with subtractive synthesis. Of course, they only allow limited range of pitch, but for percussion or complex physical sounds, it’s the best choice.

The ST4 uses 8 bit samples (although the record and replay hardware actually has 11 bit resolution). This gives it a very oldschool early nineties feeling. The recording was added as a fun feature, mainly for voice, but the microphone is sensitive enough to record music playing in the room, for instance..

A sample being displayed along with start (yellow), loop start (green) and loop end (red) pointers.
A sample being displayed along with start (yellow), loop start (green) and loop end (red) pointers.

Using the on-board REC button, you can record samples via the microphone or line input. The line input automatically supersedes the mic. You can record up to 3 seconds (64 kByte @ 20 kHz, 8 bit). While holding down REC the ST4 records. Releasing REC stops recording.

To visualize what you’ve just recorded, first make sure you are in SPL mode. Use the SEL button to activate the lower led. Then use the left and right rotary encoders. This shows the waveform stencil. There’s an automatic zoom in place that adjusts zoom relative to the distance between loop start and end (This may be removed or maybe turned off in future versions). Use shift+s to toggle between controlling loop start and sample start. This is useful if you started recording a bit too early.

Explanation of the pointers in the sample display:

Yellow: sample start
Green: loop start
Red: loop end

TODO: photos of the physical REC/toggle/rotary encoders section

Potentiometer and slider behavior

The ST4 potentiometers, or pots for short, the things underneath those knobs with blue indicators.. come in two types: with or without center detent. This means some behave like balance knobs like on your HIFI, and some behave like volume buttons. The center detent types are present, logically for panning, and also to realize the full complexity of the MOD matrix with optimal UI space. All other pots are without detent.

There’s more to it than that, though. A lot of pots, for instance everything in the Voice and LFO sections, are linear. But cutoff pots are exponential, because this makes more sense musically. If they were linear, they’d move too quickly in (sub-)bass and too slowly in the higher frequencies.

The MOD pots are also linear. Move 20 degrees off-center, then move to 40 degrees off-center. Now the modulation depth is twice what it was.

The sliders are a different story. The Sustain slider is of course linear, since it does amplitude. But on the time range sliders (A,D,R) the musician expects to have smooth relative variation over the entire time range. This is realized by a cubic curve. This gives excellent control over the short end of the scale while not making extreme jumps near the long end. The display is designed to graphically represent the linear position of the slider (0..255), while the actual time in milliseconds is displayed in text form.

After loading a module the pots are all configured to setpoints. This means you have to turn or slide the control to the fixed position to activate it. The following GUI picture shows a pot with 2 indicators. The filled one is the actual measured value, and the empty one is the set point. The set point indicator will disappear once the measured value comes close. At that moment the control becomes active and will influence the sound again.

S -> [graphic envelope display]
-> [text display]

A,D,R -> [graphic envelope display]
-> [cubic curve] -> [text display (ms)]

Potentiometer with setpoint.
Potentiometer with setpoint.

Display priorities

All controls except for mic level can be visualized on the display. This may seem like a luxury toy feature, but with setpoints it makes a lot of sense. When modules are loaded or when a track gets a program/instrument change, new setpoints are configured, but the pots will stay in their original position. They display will show setpoint and physical position too and will show the user how much knob turning should be done to actuate the control.

Several groups of controls are prioritized. This means while one group is active it will stay on the display until it is left alone for 3 seconds. At that time other controls are _not_ displayed (but of course, still usable). Prioritization is basically done to overcome the display going crazy switching between active controls when you touch 2 or more pots at the same time.

Priorities are as follows:
1) envelope sliders
2) bit crusher pots
3) sample display
4) all others

Envelope and bit crushers groups consist of composite controls. This means they are displayed based on multiple controls. The envelope graph needs all parameters A,D,S,R to be displayed. The bit crusher needs both bit resolution and sample rate for its staircase shape to be displayed.

All other pots are standalone displayed. Of course, there are many of those and chances are you’ll be using two at the same time. Moreover, you’ll want to see the setpoints on those. That’s why the ST4’s display offers visualization of 4 pots at the same time.. and if you happen to use more than 4 in a 3 second span, the least recently used pot is overwritten with the new one.

MIDI commands

The ST4 supports MIDI input on MIDI channels 1 through 4 to directly control its tracks. Each channel is then used in mono mode. For poly mode you can use channel 5. Note on / note off and pitch bend are supported on all these channels, as well all the commands listed below. Some of them only make sense in a global scope (like track-to-track detuning), but many can be applied to specific channels, and of course to channel 5 (all tracks, which may be used for poly mode). The CC’s represent literally every potentiometer on the ST4 except for the mic volume! It will also accept the MIDI beat clock commands to start and stop its tracker and control the tempo.

The ST4 can also send out MIDI information. At the moment this is limited to note on/off and beat clock. The ST4 will send out the beat according to the tracker’s tempo.

MIDI command Description Cmd/CC value channel/global
pitch bend chan + glob
pgm change 0..127 chan + glob
cc vco mod 0 0..127 → -64..+63 chan + glob
cc vcf mod 18 0..127 → -64..+63 chan + glob
cc vca mod 2 0..127 → -64..+63 chan + glob
cc vco attack 3 0..127 chan + glob
cc vcf attack 4 0..127 chan + glob
cc vca attack 5 0..127 chan + glob
cc vco decay 6 0..127 chan + glob
cc vcf decay 7 0..127 chan + glob
cc vca decay 8 0..127 chan + glob
cc vco sustain 9 0..127 chan + glob
cc vcf sustain 10 0..127 chan + glob
cc vca sustain 11 0..127 chan + glob
cc vco release 12 0..127 chan + glob
cc vcf release 13 0..127 chan + glob
cc vca release 14 0..127 chan + glob
cc panning 15 0..127 → -64..+63 chan + glob
cc volume 16 0..127 chan + glob
cc record sample 11 0..1 glob
cc resonance 71 0..127 chan
cc cutoff (coarse) 74 0..127 chan
cc osc waveform 96 0..127 chan
cc PWM 97 0..127 chan
cc detune12 98 0..127 glob
cc detune34 99 0..127 glob
cc lfo1waveform 100 0..127 glob
cc lfo2waveform 101 0..127 glob
cc lfo1range 102 0..127 glob
cc lfo2range 103 0..127 glob
cc lfo1rate 104 0..127 glob
cc lfo2rate 105 0..127 glob
cc spl loopstart 106 0..127 chan
cc spl loopend 108 0..127 chan
cc bitcrush rate 110 0..127 chan + glob
cc bitcrush bits 112 0..127 chan + glob
cc vcf cutoff fine 114 0..127 chan
cc vcf mode 115 0..3 chan + glob
cc glide 116 0..127 chan + glob
midi beat clock 248
midi beat start 250
midi beat continue 251
midi beat stop 252

Firmware update:

Firmware updates proceed via the USB-B programming port on the rear of the unit. Hook up your PC or Mac and go. For this we have created a firmware updater. The idea is just unzip, double click, and go. The latest firmware binary is included.

Detailed procedure (Mac):

  1. Download and unpack the firmware zip.
  2. Hook up your Mac with USB-A -> USB-B cable to the ST4’s port named “PRG”. You can leave the ST4 power switch on or off, it doesn’t matter.
  3. Run update_firmware.command. *right click* -> “Open With” -> “Terminal”.  This is due to MacOS security.
  4. A progress bar should show. Wait for about a minute for it to upload and DON’T POWER DOWN while it’s working!
  5. After it has finished, remove USB cable, and switch the ST4 power off and on again. This is necessary for the first startup of the new firmware.

Detailed procedure (Windows):

  1. Download and unpack the firmware zip.
  2. Install Arduino IDE, see installation for Arduino DUE and follow it completely.
  3. Get bossac.exe either from the BOSSA 1.5 msi installer below, or click bossac.exe (zip). Copy st4_firmware.bin to the same directory as bossac.exe.
  4. Hook up your PC with USB-A -> USB-B cable to the ST4’s port named “PRG”. You can leave the ST4 power switch on or off, it doesn’t matter.
  5. Open the command terminal.. and type the following (assuming com port is COM32)
    1. cd “\Program Files (x86)\BOSSA” (or wherever you installed that bossac.exe)
    2. mode com32:1200,n,8,1
    3. bossac.exe –port=COM32 -U false -w -e -b st4_firmware.bin
  6. A progress bar should show. Wait for about a minute for it to upload and DON’T POWER DOWN while it’s working!
  7. After it has finished, remove USB cable, and switch the ST4 power off and on again. This is necessary for the first startup of the new firmware.

Output from windows command prompt session:

C:\Program Files (x86)\BOSSA>mode com32:1200,n,8,1

Status van apparaat COM32:
    Baud:                  1200
    Pariteit:              None
    Databits:              8
    Stopbits:              1
    Time-out:              ON
    XON/XOFF:              OFF
    CTS-handshaking:       OFF
    DSR-handshaking:       OFF
    DSR-reactiesnelheid:   OFF
    DTR-circuit:           ON
    RTS-circuit:           ON

C:\Program Files (x86)\BOSSA>bossac.exe --port=COM32 -U false -v -w -e
-b st4_firmware.bin
Atmel SMART device 0x285e0a60 found
Erase flash
done in 0.033 seconds

Write 274076 bytes to flash (1071 pages)
[==============================] 100% (1071/1071 pages)
done in 59.049 seconds

Verify 274076 bytes of flash
[==============================] 100% (1071/1071 pages)
Verify successful
done in 55.647 seconds
Set boot flash true

Linux Procedure:

You are a hacker, you can do anything. Download the firmware zip, download the bossac binaries from the github (see below) releases. Then just hack update_firmware.command (a bash script) to use the correct tty device. The rest should be exactly the same as on Mac.


Original Kickstarter release ST4 firmware: v0.26


Nice GUI-based Windows version of the BOSSA upload tool:


BOSSA releases on github