Manual (for v1 Gecho, v0.243 firmware)

User Manual

Please note this manual is for v1, the detailed manual for v2 that extends the printed materials you are receiving with your unit is here. Channel numbers have changed so what you see below no longer applies to v2 model.


This is a legacy manual version for an older firmware version. The latest manual is here.


Powering On

When powered from batteries, please use the sliding switch to safely power off the device. It will completely disconnect the (+) pole, so no significant energy is drawn from batteries. It is perfectly safe to power the board via USB from a standard 5V power source without removing batteries (also plug/unplug the USB cable even while music is playing). This is a good way to extend battery life when you have adaptor or USB port at hand.

If your battery pack also connects to "BAT+3V" pad (leading to MCU's VBAT pin / SRAM back-up voltage), it is not disconnected at any time, to preserve user generated content or settings (this only draws very little power from batteries, having virtually no effect on their life time).

The PWR (power) LED should light up, and RDY (ready) should blink in 0.5sec intervals.

When powering via USB cable, the sliding switch does not turn device off, but it changes between normal mode (at ON position), and programming mode (at OFF). This setting is "checked" at the time of connecting power (if no batteries present), and/or pressing RST (reset). For example, if you have a bare board and it is set to OFF, and you apply power from USB, it will get into programming mode. RDY will not blink, and other LEDs will lit up in a characteristic pattern.

In this situation, to get the board running normally, not only you need to set switch to ON, but also press RST button.

Selecting a Channel

Every channel's code consists of one or more numbers between 1 and 4, so they can be typed on the four-buttons keyboard. For example, to select channel #1234, press four buttons in a row, then press SET.

In some channels, SET can select an alternative mode, depending on whether you just press it or hold it for a second. All basic song-playing channels can run in Low-pass or High-pass mode. Normally, the Low-pass is selected, with the exception of channel #1 which uses High-pass as default. So, if you - after keying in the channel number - hold SET for a second, instead of just pressing it briefly, an alternative mode is selected (in this case, High-pass filters instead of a default Low-pass).


Currently Available Channels (version 0.243)

The channels marked WIP are work in progress and may not run well. Some numbers are also reserved for future use and currently do nothing, but they are listed so you know what to expect there.

  • 1: Demo song #1 with melody and high-pass filters as default
  • 2: Demo song #2 with melody - "Freedom of Creation" advert
  • 3: Picks random song out of basic demo songs (#11,12,13,22,23) and play it with low-pass filters
  • 4: Demo song #21 - "Ghost in the Shell" - used in "Assembly machines - Making of Synth" video (chords only)
  • 11: Pure white noise
  • 12: Non-interactive, slowly evolving low-pass filters - "Song of Wind and Ice"
  • 13,14: Non-interactive, static low-pass filters "Distant Ocean"
  • 21-24: Noise/resonance effects controlled by sensors, four different settings:
    • 21: Waves of the Sea
    • 22: Nostromo
    • 23: Alien Spaceship
    • 24: Combined (4 levels - each sensor different cut-out frequency)
  • 31: Theremin-like behaviour driven by magnetic ring (WIP)
  • 32: Theremin driven by sensors (WIP)
  • 33: DCO Synth, 24 oscillators bound in parallel, directly controlled by sensors
  • 34: DCO Synth, with locking mechanism and MIDI. When you press SET, parameters are locked, then you can hold buttons 1-4 to unlock individual one and affect it by related sensor. The first parameter is pitch, and can be controlled by a midi keyboard if connected
  • 41-44: Custom song programming modes. First, select how many chords you want by pressing buttons 1 to 4. You can have from 1x1 to 8x4 chords total (current setting is displayed by red and orange LEDs). Press SET to confirm. Then, input individual chords:
    • 41: Input chords by buttons: 1/2 to move chord's base note up and down. 3/4 to move to next and previous chords. Combination of 1+2, 1+3 and 1+4 (hold 1 and press 2,3 or 4 once or more times) to modify the chord (1+2: minor/major, 1+3: move 2nd note around, 1+4 move 3rd note around)
    • 42: Input chords by magnetic ring, by selecting individual notes one by one. After a note is held for one second, it is remembered. After three notes are set, it replays chord and moves to next chord, waiting for new notes. Buttons 3 and 4 move to previous/next chord, allowing for replacing (e.g. if captured incorrectly)
    • 43: Input from microphones - works similar to previous mode, but notes are recognized from environment. You need a clear source of sound to get good results
    • 44: Input from pickups/line-in, works similar to previous mode, but notes are recognized from attached guitar or other signal source

    After enough chords set, press SET button to finish programming. Blinking red and orange LEDs will indicate if the composition was saved - if blinking more times and faster, it means not enough chords was programmed - use button 4 to go through the whole sequence to check. If LEDs blink only twice and slow, chord progression is saved to the memory and starts playing. You can play it at any time (see #111) or get back to editing (see #1111)

  • 111: Plays recently generated song (loads user data from persistent memory). As with any other channel, you can hold SET for longer to get into Hi-pass filter mode
  • 113: Play notes received from the Gecho App, using sampled instrument "toy box"
  • 123: Configure Tempo (range is 15 to 330 BPM). Use buttons 1 and 2 to go down/up by 5 BPM, button 3 to set default 120 BPM. The current setting is indicated by LEDs in human-readable way: Red represent hundreds, Orange+Blue represent tens and White represent units: [100*r + 10*(o+b) + w]. So, if you see 1 red, 3 orange and 5 white LEDs glowing, the tempo is 135 BPM.
  • 222: Generate random chord progression - as explained here
    • 222[...]: More buttons pressed allow to set a specific "random seed" (initial value), in such case the generated song is always the same per channel. This allows you to access again any interesting sequence that may be hiding under that combination.
  • 231: Simple drum kit - four samples, controlled by sensors
  • 232: Simple drum kit with echo
  • 233: Simple drum kit over song #2 - for tutorial and demonstration video
  • 234: Basic drum sequencer - as explained in this tutorial and demonstration video. NEW: To turn metronome off and on again, press button #4.
  • 314: Songs of Pi - picks a random position within first 100,000 digits of π and start generating chord progressions from there
    • 314[...]: More buttons pressed allow to select a particular position within decimal representation of π, starts generating a song from there
  • 321: Directly listen to signal coming via IR sensors. You can hear for example buzzing from IR sensor in your mobile phone, or TV remote
  • 322: Directly listen to signal coming from magnetic sensors, this may require strong enough alternating field to hear something (e.g. rotating magnet will produce quiet humming)
  • 323: All LEDs test (for PCB/soldering testing)
    • 3231: Lit up each LED one by one (helps discover cold junctions or solder bridges)
    • 3232: Lit up all LEDs then turn off each one by one (helps discover cold junctions or solder bridges of different kind)
  • 324: Magnetic sensor calibration test - red and white rows react to a full range of magnetic sensor influenced by e.g. mangetic ring
  • 331: Notes recognition - Goertzel detectors or auto-correlation test via microphones
  • 332: Notes recognition - Goertzel detectors or auto-correlation test via piezo pickups/line-in input
  • 333[...]: Access code lock for Gechologists part of the website
  • 341: Direct monitor of unaltered signal from microphones
  • 342: Direct monitor of signal from microphones, with echo
  • 343: Direct monitor of unaltered signal from pickups/line-in
  • 344: Direct monitor of signal from pickups/line-in, with echo
  • 411: Real-time Granular Sampler - as explained in this tutorial and demonstration video
  • 412: Granular Sampler with a Chord progression - as seen here
  • 413: Granular Sampler with arbitrary song: After selecting channel, it waits for another number (and SET button) which selects song (can be 111 for recently programmed one)
  • 421: (new) Decaying Reverb with increasing buffer size, as demonstrated in this video.
  • 422: (new) Decaying Reverb with decreasing buffer size, otherwise the same.
  • 423: (new) Decaying Reverb, controllable with sensors: S1 tunes it down (the perceived note/frequency depends on buffer length), S2 starts increasing the buffer as in #421, S3 starts decreasing buffer as in #422, S4 tunes it up.
  • 441: (new) Bytebeat, a chiptune-like mathematically generated "songs", as demonstrated in this video.
  • 1111: Editing of stored song. Works exactly like #41 (starts from last programmed or generated song, instead of empty space)
  • 1122: All drum samples test - plays four samples in sequence
  • 1211: CV direct notes test
  • 1212: MIDI out test - will transmit a few notes in sequence
  • 1213: [reserved] MIDI record and playback test (WIP)
  • 1214: CV/Gate test - CV1 controls voice, CV2 controls drum sample (WIP)
  • 1223: MIDI HW signals direct test - if you wire OUT to IN (plus to plus, minus to minus), pressing button 1 should make orange LEDs go off
  • 1234: Quick test for all buttons and LEDs
  • 4111: Demo song #11 - extended version of #1 (chords only, no melody)
  • 4112: Demo song #12 - "Canon in D" by Johann Pachelbel
  • 4113: Demo song #13 - random composition by Mario
  • 4114: XMAS Song, melody played by a sampled instrument (toy box), for tutorial with code samples
  • 4121: Demo song #21 - "Ghost in the Shell" - used in "Assembly machines - Making of Synth" video (with melody)
  • 4122: Demo song #22 - "Blade Runner - Rachel's Song" (chords only, no melody)
  • 4123: Demo song #23 - random composition by Mario
  • 4141: Slowly changing A minor and major chords plus single notes
  • 4142: Continuous A minor chord
  • 4143: Continuous A major chord
  • 4144: Continuous note A over more octaves
  • 11223: Acoustic Location Experiment - as explained in this tutorial
  • 112233: Show firmware version number (display by LEDs in BCD coded format)
  • 223344: Show unit serial number (display by LEDs in BCD coded format)
  • 43214321: Reset all user settings to default (volumes, delays, inputs)


Buttons during Play

Normally (and in most channels) the buttons 1-4 control various parameters:

  • Button 1: Decrease headphones volume
  • Button 2: Increase headphones volume
  • Button 3: Cycle through various delay lengths - press it again to get to next setting (initially, it is set to 0.5s):
    • 3/4s (750ms)
    • 1s
    • 1.25s (currently maximum with stereo at 22.5kHz sampling rate)
    • 1/3s (333ms)
    • 1/4s (250ms)
    • 1/6s (167ms)
    • 1/8s (125ms)
    • 1/12s (83ms)
    • By BPM (1/1)
    • By BPM (1/2)
    • By BPM (1/3)
    • By BPM (1/4)
    • By BPM (3/4)
    • delay off (useful for recording, if you want to apply it later)
    • back to default 1/2s

    How the "By BPM" modes work: The buffer length is adjusted to match current BPM in such a way that echo plays well with timing of the song. For example, at 120 BPM (playing 2 melody notes per second), with setting of (1/2), the buffer needs to accommodate 500ms of sound. If BPM goes up, buffer needs to shorten accordingly. If BPM goes down to 50%, buffer needs to double in size. Due to memory limitations, this is not achievable at every BPM. If there is not enough memory, delay is shortened by one half, so the timing of tempo vs delay stays in similar fractional relation. However, combining non-BPM adjusted delay with tempo other than 120BPM often yields very interesting results.

  • Button 4: Switch between microphones, pickups input and off


More Settings

If you press SET during play, you get access to one of four groups of settings. Press SET one or more times to select a particular group, then use buttons 1-4 to change the desired parameter. Row of red LEDs is used to indicate the current level of a particular setting between its minimal and maximal value.

If you don't change anything for 3.5 seconds, this mode completes and buttons revert back to normal operation.

Settings Group 1 - Equalizer:

  • Button 1: Decrease treble
  • Button 2: Increase treble
  • Button 3: Decrease bass
  • Button 4: Increase bass

Settings Group 2 - Internal volumes:

  • Button 1: Decrease OpAmp mixing volume - this affects sensitivity of microphones or pickups input. The setting changes slower than others as there is wider range to cover, you'd probably need to hold the button for longer time to observe any impact
  • Button 2: Increase OpAmp mixing volume (in a similar manner as previous one)
  • Button 3: Decrease Master volume - this is the analog volume after DAC/DSP block, affected by limiter
  • Button 4: Increase Master volume

Settings Group 3 - Tempo and melody voice:

  • Button 1: Decrease tempo by 5 BPM, it works the same as channel #123
  • Button 2: Increase tempo by 5 BPM
  • Button 3: Set tempo to default value of 120 BPM
  • Button 4: Select method for generating the melody voice (if present in song). By default one of the LP/HP filter pairs is used, but it can be changed to a sampled "toy box" sound.

Settings Group 4 - Mixing and Power Saving options:

  • Button 1: 50% Dry Mixing - let part of the incoming signal be present in the output (this is particularly useful with other small synths, e.g. like demonstrated here.
  • Button 2*: Disable Low-battery indicator (in case the blinking after every reset is in the way, or if you don't have battery installed at all)
  • Button 3*: Disable sensors altogether (useful if you want to use it with closed lid but don't want the lid to trigger all sensors to the maximum)
  • Button 4*: Turn all LEDs off (for saving power, or if the light is too disturbing in the dark - only the PWR LED will continue to glow, and in channels that use sensors, RDY LED will blink too, as it is also driving sensors timing)

*This settings is work in progress - not yet implemented, but planned in future updates.


Quick Start Card

And last but not least, here is a card, summarizing basic controls (a higher-resolution PDF for printing is here):


Legacy versions of the manual

These pages are only useful if you haven't upgraded to the newer version yet

Manual v0.192/0.193
Manual v0.207
Manual v0.219
Manual v0.224