How to use
The preset and user patches can be accessed using the pushbuttons on the PCB marked PROGRAM. New
patches can be created and stored in the dsPIC chip using a Windows desktop Patch Editor app. Typically this
works in conjunction with a USB-to-MIDI adapter connected to the PC and the MIDI socket on Bleep-o-tron.
(Note that the USB-to-MIDI adapter must be able to handle MIDI SysEx messages correctly for the Patch
Editor to work.)
The fundamental sound generators of Bleep-o-tron are a pair of oscillators or ‘timbres’. Different waveforms
are available for each of these oscillators and they can be combined to produce more complex sounds. In
addition, each oscillator can output white noise.
The amplitude (volume) and pitch (frequency) of each timbre oscillator is under the dynamic control of both
an envelope and a low-frequency oscillator. The modulation (the degree to which the oscillator outputs a
simple sine wave or a more complex waveform) is also controllable by the same means. (Modulation is
equivalent to low-pass filtering in a traditional analogue synthesiser.)
The second oscillator can be detuned or offset relative to the first. This can be used to further ‘thicken’ a
sound. Detuning can be done by fractions of a semitone (known as ‘cents’), and can cause tremolo-type
effects as the two oscillators move into and out of phase with each other. Offsetting by a whole number of
semitones is equivalent to a two-note chord. Some intervals are very discordant. Whole octave intervals can
add body to a sound.
The gain or amplitude of each timbre can be independently adjusted. This is useful for making one
component of a sound dominant relative to the other. The default timbre gain is ¾ of the maximum.
Classic four-stage attack-decay-sustain-release envelopes are available for both oscillators to control their
amplitude, pitch and modulation. The level and period of the four stages can be individually adjusted for all
six envelopes, and envelopes can be sustained for as long as a key is held down.
An envelope can be copied to another and reset to the defaults.
Low-frequency oscillators, or LFOs, allow effects such as tremolo and vibrato. The amplitude, frequency and
waveform of each LFO can be independently controlled. Six LFO waveforms are available - sine, square,
triangle, rising sawtooth, falling sawtooth and noise. There is an option to delay an LFO until the sustain
period of its associated envelope.
One LFO can be copied to another.
Portamento is available which causes a glide between pitches when two notes are pressed in succession (as
opposed to the normal discrete jump from one pitch to the other). There are two types of portamento -
constant rate which means that small spans on the keyboard are covered more quickly than longer spans,
and constant time which means that glides take the same amount of time irrespective of the span length.
‘Retrigger’ causes all envelopes and LFOs to be restarted when a second note is pressed before a first has
finished playing. It can result in glitches when notes are pressed in quick succession so is not normally used,
but might be useful in certain circumstances.
A flanger is available which acts as a dynamic filter removing a set of regularly-spaced frequencies from the
sound spectrum (i.e., a comb filter). The position of the filter notches is under the control of a separate LFO,
and the range, waveform, speed of frequency sweep and dry-wet mix are all controllable. (The flanger is
implemented as a variable-length delay line and its parameters affect the instantaneous length of the delay
