Audio Damage ADM14 BoomTschak Eurorack Drum Module User Guide
- June 17, 2024
- AUDIO DAMAGE
Table of Contents
User Guide BoomTschak User’s Guide
Audio Damage, Inc.
1 November 2016
The information in this document is subject to change without notice and does
not represent a commitment on the part of Audio Damage, Inc. No part of this
publication may be copied, reproduced or otherwise transmitted or recorded,
for any purpose, without prior written permission by Audio Damage, Inc.
© 2016 Audio Damage, Inc. All rights reserved.
Brief Overview
BoomTschak is an Eurorack module for synthesizing drum and percussion sounds.
It contains a VCO, three envelope generators, a noise source, a multi-mode
VCF, and several VCAs. Its circuitry is completely analog.
Below is an image of its panel and a description of the controls. This summary
will cover just about everything that you need to know to use BoomTschak, but
after this summary we’ll provide more detailed descriptions and some
background information.
If you can’t stand reading manuals, we’ve got you covered. There’s a video
providing an overview of BoomTschak’s operation on YouTube here:
https://www.youtube.com/watch?v=2h267q8DlFY
1.1. Knobs and Switches
PITCH – sets the frequency of the VCO
BEND DEPTH — controls how much the pitch-bend envelope generator changes the
frequency of the VCO. This is a bidirectional control; at its center
position, the EG has no effect on the VCO.
BEND DECAY – sets the decay time of the pitch-bend EG.
BEND SHAPE — varies the shape of the pitch-bend EG from a sharp exponential
curve to a linear ramp.
AMP DECAY – sets the decay time of the envelope generator which controls the
VCA for the VCO, and hence how long the VCO tone is heard.
AMP SHAPE – varies the shape of the VCO amplitude EG from a sharp exponential
curve to a linear ramp.
WAVE Switch — switches the VCO output between a triangular wave and a
sinusoidal wave.
KLIK TONE — changes the brightness of a short click added to the beginning of
the sound.
WAVESHAPER – controls a simple wave-folder which changes the shape of the
VCO’s signal.
FILTER FREQ – sets the frequency of the multi-mode filter for the noise
source.
FILTER Q – sets the resonance of the filter.
MOD SOURCE Switch — choose the source of modulation for the filter frequency.
There are three options: the amplitude envelope generator for the noise
source, the pitch bend oscillator for the VCO, and the VCO’’s signal.
MOD DEPTH – controls how much the modulation signal selected with the MOD
SOURCE switch changes the filter frequency. This is a bidirectional control;
at its center position, the filter frequency will not be changed by the
modulation signal.
FILTER MODE Switch — chooses one of three filter response modes: low pass,
band pass, or high pass.
AMP DECAY – sets the decay time of the envelope generator which controls the
VCA for the noise source, and hence how long the noise is heard.
AMP SHAPE – varies the shape of the noise amplitude EG from a sharp
exponential curve to a linear ramp.
MIX — varies the relative loudness of the VCO and the noise source. At its
center position, the noise source and VCO have roughly equal loudness. Rotate
the knob counter-clockwise to hear
more of the VCO, rotate it clockwise to hear more noise.
LEVEL — sets the overall output level of the module.
MANUAL Button — press this to trigger the module manually. Use it while
setting BoomTschak’s knobs or for live improvisation.
1.2. Jacks
TRIGGER — Apply a positive-going rectangular wave to this jack to trigger the
module. A +5V signal is best but the module will trigger at lower voltages.
VELOCITY — A control-voltage input for varying the loudness of the module.
Positive voltages increase the loudness; negative voltages decrease it.
CHOKE — A positive-going rectangular pulse applied to this input will cut off
(choke) the output of the module.
FILTER INPUT — Plugging a signal into this jack will bypass the module’s noise
source, passing the signal through the filter.
OUTPUT—hopefully this one needs no explanation.
There are also five control-voltage jacks associated with some of the knobs.
Applying a positive voltage to these jacks has the same effect as turning the
associated knob clockwise; applying a negative voltage has the opposite
effect.
Detailed Description
Traditionally, drum and percussion sounds are thought of as having two
distinct sonic components. The first is a perceivable pitch, created by a
resonant body such as the air within the shell of a bass drum or tom, or the
resonant frequency of a metal bar as found on a Xylophone. The second
component lacks a distinct pitch and is produced by events such as the initial
contact between a drum stick and the drum head or the rattle of the wires on a
snare drum. In this vein, BoomTschak has two sources of sound signals: an
oscillator and a filtered noise generator. These two signals are mixed
together to produce BoomTschak’s output.
2.1. Oscillator
The oscillator, known as a voltage-controlled oscillator or VCO for short,
generates a periodic signal with a frequency of less than 10Hz up to about
1.3KHz. The initial pitch of the VCO is set with a panel knob but can also be
modulated with an envelope generator and/or controlled by an external voltage.
The VCO has a switch which selects one of two wave shapes: a nearly sinusoidal
shape producing a clear but soft tone, and a triangle wave which produces a
brighter tone.
2.1.1. Wave Shaper
The selected oscillator signal is sent through a wave shaper which alters the
tone or timbre of the wave. The wave shaper works by folding the peaks of the
wave. Turning up the knob produces more folding, as shown in this illustration
for the triangle wave: 2.1.2. Pitch Modulation
BoomTschak’s BEND DECAY and BEND SHAPE knobs control an envelope generator
which varies the pitch of the oscillator. The pitch of many real-world drums
starts slightly sharp and bends downward as the sound fades. A few percussion
instruments, such as tablas, can be made to bend upwards in pitch. Electronic
drums, unconstrained by physical mechanics, can bend wildly.
The BEND DEPTH knob controls how much the oscillator’s pitch changes. It is a
bidirectional control; if placed at its center position, the pitch will be the
same for the duration of the sound. If you turn the knob clockwise, the pitch
will start sharp and bend downwards. Turn the knob the other direction to make
the pitch bend upwards.
Besides the obvious creation of dramatic frequency swoops, the pitch bend
controls can also add character to the attack of the sound. With the
oscillator set to a fairly low frequency, try turning the BEND DECAY and BEND
SHAPE knobs fully anti-clockwise, then slowly turn the BEND DEPTH knob
clockwise from its center position.
2.1.3. Pitch Input Jack
The frequency of the oscillator can also be controlled directly by a signal
applied to the PITCH INPUT jack. The VCO responds to input voltages with the
usual convention of a change of one volt producing a change of one octave.
Yes, this means that you can play melodies or bass lines with BoomTschak.
2.2. Filtered Noise Generator
The noise generator produces white noise, that is, noise that is equally loud
at all frequencies.
This noise passes through a voltage-controlled filter which removes some of
the noise frequencies. The filter has three different modes, selected with
panel switch. The modes are as usual for a VCF: low-pass, which removes high
frequencies; high-pass, which removes low frequencies; and band-pass, which
removes low and high frequencies but preserves a range of frequencies in the
middle. The range of frequencies is nominally controlled by a panel knob but
can also be affected by an external control voltage and one of several intemal
signals, as described below.
The filter also sports a resonance knob which causes the filter to emphasize
the sound at the corner or center frequency. If you turn this knob up far
enough, the filter will oscillate, creating a tone. This sounds kind of rough
since there is still white noise entering the filter. However, if you plug one
end of a loose cable into the Filter Input jack, the noise will be removed and
you’ll hear a steady tone whose timbre varies slightly depending on the
position of the Filter Mode switch.
2.2.1. Filter Modulation
Setting the filter’s frequency with its panel knob allows you to change the
timbre of BoomTschak’s noise source (or that of an external signal). That
frequency can be changed, or modulated, by one of several signals while
BoomTschak plays, imparting some motion to the timbre. There are three
internal sources of modulation available, selectable with the MOD SOURCE
switch: the noise-amplitude envelope generator, the oscillator pitch-bend
envelope generator, and the oscillator’s audio signal (post-VCA and wave
shaper). The MOD DEPTH knob controls how much the chosen signal modulates the
filter’s frequency. It is a bidirectional control; if it’s set to its center
position, the filter won’t be modulated. Turn the MOD DEPTH knob clockwise to
make the filter frequency increase in response to the modulation signal, and
turn it anti-clockwise to make the filter frequency decrease. For example, if
you’re looking for the classic noise-with-downward-sweeping-filter effect.
select one of the EGs with the MOD SOURCE switches and rotate the MOD DEPTH
knob clockwise from center.
The OSC position of the MOD SOURCE switch presents some interesting
possibilities. If you turn the oscillator frequency way down to a sub-audio
rate, you can use it as an LFO to modulate the filter, creating rapid flutters
or slow undulations. If you turn the FILTER Q knob all the way up to make the
filter oscillate, you can modulate its pitch with the oscillator, creating
video-game laser noises, FM-synth pings, and so on.
Finally, the filter has a jack labeled FREQ. Any signal applied to this input
will alter the filter’s frequency, adding to whatever modulation you’ve
created with the MOD SOURCE and MOD DEPTH knob. Positive voltages increase the
frequency; negative voltages decrease it. Audio-rate signals will create FM
effects, particularly if the filter is oscillating.
2.2.2. External Filter Input
As mentioned above, plugging something into the Filter Input jack disables
BoomTschak’s noise source and passes whatever you plug in into the filter. You
can, for example, plug your favorite oscillator into this jack and create a
simple but quite respectable bass synth using BoomTschak’s filter and
accompanying EG and VCA, maybe mixing in some of BoomTshak’s oscillator as a
sub-tone.
2.3. Envelope Generators
BoomTschak has three envelope generators. When BoomTschak is triggered, the
envelope generators (EGs for short) produce a voltage that jumps instantly
from zero to a peak value and then decays back down to zero.
Each EG has two controls: a Decay knob and a Shape knob. The Decay knob
controls how long it takes for the EG’s voltage to decay back to zero after
being triggered. This time can be as short as about 1/10™ of a second or as
long as about six seconds.
The Shape knob controls how the voltage decays. If the Shape knob is rotated
fully anti-clockwise, the voltage drops sharply at first and then slows as it
approaches zero. If the Shape knob is rotated fully clockwise, the voltage
decreases to zero at the same rate. These different shapes are indicated by
icons on the panel; here’s an illustration which shows typical curves: Even
though the Decay and the Shape knobs operated independently, the EG will
subjectively sound shorter as the Shape knob is rotated anti-clockwise since
most of the energy is present near the beginning of the sound.
2.3.1. Decay Jack
In addition to the Decay knob, the envelope generators have a control-voltage
input jack.
Positive voltages increase the time it takes the envelope to fade out;
negative voltages decrease the time. One example of a use for these input
jacks is to simulate a high-hat, using a control voltage to vary the sound’s
decay time between short and long.
2.4. Output Controls
The last knobs on BoomTschak’s panel don’t hold many surprises. The MIX knob
varies the relative amounts of the signals from the oscillator and the
filtered noise source. At its center position, the signals are mixed in equal
amounts (although their actual audible levels depend on other things, such as
the filter’s mode and frequency). Turn the knob to the left and you’ll hear
more of the oscillator, turn it to the right and you’ll hear more of the
filtered noise.
The MIX jack lets you vary the balance of the signals with an external control
voltage. Positive voltages increase the level of the oscillator and decrease
the level of the noise, negative voltages do the opposite. Since the two
sections of BoomTschak are flexible enough to create complete sounds by
themselves, controlling the mix with an external voltage—such as from our
Sequencer 1 Eurorack sequencer—is a viable way to produce two or more distinct
drum parts from one module.
The LEVEL knob does what you expect: it sets the overall loudness or volume of
BoomTschak’s output.
2.5. Trigger, Choke, and Velocity Jacks
The TRIGGER jack makes BoomTschak make sound. The most appropriate signal for
this input is a pulse that rises from Ov to +5V or higher, and lasts around
5Smsec or longer. BoomTschak will trigger on pulses with a lower peak level,
but you’ll hear differences in its sound which may or may not be useful.
The CHOKE jack expects the same sort of signal as the TRIGGER jack. An
incoming pulse will cause all three of BoomTschak’s envelope generators to
cease their decay and immediately drop to zero, silencing the sound. The
obvious use of this jack is to simulate a cymbal choke, in which the player
strikes a cymbal and then grabs its rim to silence it. The less obvious use is
to apply periodic or random signals to this input to produce glitchy effects.
The VELOCITY jack borrows its name from MIDI parlance, allowing you to control
BoomTschak’s overall loudness with an external voltage. The input voltage is
sampled when a trigger pulse is received. Positive voltages increase the
output level and negative voltages decrease it.
And Finally…
Thank you for purchasing BoomTschak. We make every effort to ensure your satisfaction with our products, and want you to be happy with your purchase. Please write to us at info@audiodamage.com if you have any questions or comments.