Dr. Octo Rex synth parameters

The Dr. Octo Rex synth parameters are used for shaping and modulating the sound of the REX loops. These parameters are familiar synth parameters, similar to the ones in the synthesizers; The Subtractor and the Malström, and in the samplers; the NN-19 and the NN-XT. It is important to remember that these parameters do not alter the REX files in any way, only the way they will play back.

Most of the synth parameters are global, in the sense that they will affect all slices in the REX files as well as all REX loops in all eight Loop Slots.

All Dr. Octo Rex synth panel settings are stored in the Song (and in the Dr. Octo Rex patch file if you choose to save the settings as a patch).

Select Loop & Load Slot

Click any of the eight Select Loop & Load Slot buttons to select a loaded REX loop for editing, or to load a new REX file to.

If no loop is already present in the selected Loop Slot, the Waveform Display will be blank. Otherwise, the display shows a graphical readout of the REX loop and info (name, original loop tempo, number of bars and signature).

Click the Follow Loop Playback button to “synchronize” the Select Loop & Load Slot buttons to the Loop Slot buttons on the front panel.

This way, the currently playing loop will always be displayed in the Waveform Display. If you’re using Pattern Automation in the sequencer, where the Slots are switched during playback, you might want to deactivate the Follow Loop Playback function to make it easier to edit a specific loop.

Refer to “Adding Loops” for info on how to load REX files and to “Editing in the Waveform Display” for info about editing the REX loop.

Loop Transpose

Set the transposition of individual loops in the Dr. Octo Rex by using the Loop Transpose knob to the bottom left on the panel, or by clicking on the keyboard display below the knob.

You can raise or lower the pitch in 12 semitone steps (+/–1 octave).

•	The Loop Transpose value can also be controlled via MIDI, by pressing a key between C-2 and C0 (with C-1 resetting the transpose value to zero).

This way you can also record transposition changes in the sequencer.

To control Loop Transpose via MIDI, the Note To Slot parameter must be set to the Loop Slot you want to control, see “Note To Slot”.

It’s also possible to set a global transpose value that affects all REX loops equally, see “Global Transpose”.

Loop Level

Set the individual levels for the loops in the Loop Slots with the Loop Level knob.

This lets you match the levels of the loops in the 8 Loop Slots.

Oscillator section

For a REX file, the audio contained in the slices are what oscillators are for a synthesizer, the main sound source. The following settings can be made in the Osc Pitch section of the Dr. Octo Rex:

Env. A

This parameter determines to what degree the overall pitch of all the REX files will be affected by the Filter Envelope (see “Filter Envelope”). You can set negative or positive values here, which determines whether the envelope curve should raise or lower the pitch.

Oct and Fine - Setting the overall Pitch

You can change the overall pitch of all REX files in the 8 Loop Slots in three ways:

In octave steps.

This is done using the Oct knob. The range is 0 - 8, with “4” as default.

In semitone steps.

This is done by using Global Transpose controls, see “Global Transpose”.

In cents (hundredths of a semitone).

The range is -50 to 50 (down or up half a semitone).

To transpose individual REX loops, use the Loop Transpose parameter, see “Loop Transpose”.

To tune an individual slice in a REX loop, select it and use the Pitch parameter below the waveform display, see “Editing in the Waveform Display”.

Mod. Wheel

The Modulation wheel can be set to simultaneously control a number of parameters. You can set positive or negative values, just like in the Velocity Control section. The following parameters can be affected by the modulation wheel:

| Parameter	| Description
F. Freq	This sets modulation wheel control of the filter frequency parameter. A positive value will raise the frequency if the wheel is pushed forward. Negative values invert this relationship.
F. Res	This sets modulation wheel control of the filter resonance parameter. A positive value will increase the resonance if the wheel is pushed forward. Negative values invert this relationship.
F. Decay	This sets modulation wheel control for the Filter Envelope Decay parameter. A positive value will increase the decay if the wheel is pushed forward. Negative values invert this relationship.

Velocity section

Velocity is usually used to control various parameters according to how hard or soft you play notes on your keyboard. A REX file does not contain velocity values on its own. And when you create sequencer track data by applying the “Copy Loop To Track” function, all velocities are set to a default value of “64”. As velocity information is meant to reflect variation, having them all set to the same value is not meaningful if you wish to velocity control Dr. Octo Rex parameters.

There are basically two ways you can apply “meaningful” velocity values to REX files:

•	After creating track data, you can edit velocity values in the Velocity Lane in the sequencer.

•	You can play slices in real time on your keyboard. The resulting data will have velocity values reflecting how the notes were struck when you played.

When velocity values have been adjusted, you can control how much the various parameters will be affected by velocity. The velocity sensitivity amount can be set to either positive or negative values, with the center position representing no velocity control.

The following parameters can be velocity controlled:

| Parameter	| Description
F. Env	This sets velocity control for the Filter Envelope Amount parameter. A positive value will increase the envelope amount with higher velocity values. Negative values invert this relationship.
F. Decay	This sets velocity control for the Filter Envelope Decay parameter. A positive value will increase the Decay time with higher velocity values. Negative values invert this relationship.
Amp	This let’s you velocity control the overall volume of the file. If a positive value is set, the volume will increase with higher velocity values.

The Filter Section

Filters are used for shaping the overall timbre of all REX files in all 8 Loop Slots. The filter in Dr. Octo Rex is a multimode filter with five filter modes.

Activate or deactivate the filter completely by clicking the Filter On button.

The filter is active when the button is lit.

Mode

With this selector you can set the filter to operate as one of five different types of filter. These are as follows:

•

Notch

A notch filter (or band reject filter) could be described as the opposite of a bandpass filter. It cuts off frequencies in a narrow midrange band, letting the frequencies below and above through.

•	High-Pass (HP12)

A highpass filter is the opposite of a lowpass filter, cutting out lower frequencies and letting high frequencies pass. The HP filter slope has a 12 dB/Octave roll-off.

•	Bandpass (BP 12)

A bandpass filter cuts both high and low frequencies, while midrange frequencies are not affected. Each slope in this filter type has a 12 dB/Octave roll-off.

•	12 dB Lowpass (LP 12)

This type of lowpass filter is also widely used in classic analog synthesizers (Oberheim, early Korg synths, etc.). It has a gentler slope (12 dB/Octave), leaving more of the harmonics in the filtered sound compared to the LP 24 filter.

•	24 dB Lowpass (LP 24)

Lowpass filters lets low frequencies pass and cuts out the high frequencies. This filter type has a fairly steep roll-off curve (24dB/Octave). Many classic synthesizers (Minimoog/Prophet 5 etc.) used this filter type.

Filter Frequency

The Filter Frequency parameter (often referred to as “cutoff”) determines which area of the frequency spectrum the filter will operate in. For a lowpass filter, the frequency parameter could be described as governing the “opening” and “closing” of the filter. If the Filter Freq is set to zero, none or only the very lowest frequencies are heard, if set to maximum, all frequencies in the waveform are heard. Gradually changing the Filter Frequency produces the classic synthesizer filter “sweep” sound.

Note that the Filter Frequency parameter is usually controlled by the Filter Envelope (see “Filter Envelope”) as well. Changing the Filter Frequency with the Freq slider may therefore not produce the expected result.

Resonance

The filter resonance parameter affects the character of the filter sound. For lowpass filters, raising the resonance will emphasize the frequencies around the set filter frequency. This produces a generally thinner sound, but with a sharper, more pronounced filter frequency “sweep”. The higher the resonance value, the more resonant the sound becomes until it produces a whistling or ringing sound. If you set a high value for the resonance parameter and then vary the filter frequency, this will produce a very distinct sweep, with the ringing sound being very evident at certain frequencies.

•	For the highpass filter, the resonance parameter operates just like for the lowpass filters.

•	When you use the Bandpass or Notch filter, the resonance setting adjusts the width of the band.

When you raise the resonance, the band where frequencies are let through (Bandpass), or cut (Notch) will become narrower. Generally, the Notch filter produces more musical results using low resonance settings.

Envelope section

Envelope generators are used to control several important sound parameters in analog synthesizers, such as pitch, volume, filter frequency etc. In a conventional synthesizer, envelopes govern how these parameters should respond over time - from the moment a note is struck to the moment it is released. In the Dr. Octo Rex device however, the envelopes are triggered each time a slice is played back.

There are two envelope generators in the Dr. Octo Rex, one for volume, and one for the filter frequency (and/or pitch). Both have the standard four parameters; Attack, Decay, Sustain and Release

Please refer to “Envelopes - General” in the Subtractor chapter for a description of the basic envelope parameters.

Amplitude Envelope

The Amp Envelope governs how the volume of each slice should change over time, from the time it is triggered (the slice note starts) until the slice note ends. This can be used to make a loop more distinct (by having a snappy attack and a short decay time) or more spaced-out (by raising the attack time).

Filter Envelope

The Filter Envelope can be used to control two parameters for all REX loops in the 8 Loop Slots; filter frequency and overall loop pitch. By setting up a filter envelope you control how the filter frequency and/or the pitch should change over time for each slice.

The Amount parameter determines to what degree the filter frequency will be affected by the Filter Envelope. The higher the Amount setting, the more pronounced the effect of the envelope on the filter.

Try lowering the Frequency slider and raising Resonance and Envelope Amount to get the most effect of the filter envelope!

LFO section

LFO stands for Low Frequency Oscillator. LFOs are oscillators in the sense that they generate a waveform and a frequency. However, there are two significant differences compared to normal sound generating oscillators:

•	LFOs only generate waveforms with low frequencies.

•	The output of the two LFOs are never actually heard. Instead they are used for modulating various parameters.

The most typical application of an LFO is to modulate the pitch of a (sound generating) oscillator or sample, to produce vibrato. In the Dr. Octo Rex device, you can also use the LFO to modulate the filter frequency or panning.

Waveform

LFO 1 allows you to select different waveforms for modulating parameters. These are, from top to bottom:

| Waveform	| Description
Triangle	This is a smooth waveform, suitable for normal vibrato.
Inverted Sawtooth	This produces a “ramp up” cycle. If set to control pitch (frequency), the pitch would sweep up to a set point (governed by the Amount setting), after which the cycle immediately starts over.
Sawtooth	This produces a “ramp down” cycle, the same as above but inverted.
Square	This produces cycles that abruptly changes between two values, usable for trills etc.
Random	Produces random stepped modulation to the destination. Some vintage analog synths called this feature “sample & hold”.
Soft Random	The same as above, but with smooth modulation.

Destination

The available LFO Destinations are as follows:

| Destination	| Description
Osc	Selecting this makes LFO control the pitch (frequency) of the REX file.
Filter	Selecting this makes the LFO control the filter frequency.
Pan	Selecting this makes the LFO modulate the pan position of the REX file, i.e. it will move the sound from left to right in the stereo field.

Sync

By clicking the SYNC button you activate/deactivate LFO sync. The frequency of the LFO will then be synchronized to the song tempo, in one of 16 possible time divisions. When sync is activated, the Rate knob (see below) is used for setting the desired time division.

Turn the knob and check the tooltip for an indication of the time division.

Rate

The Rate knob controls the LFO’s frequency. Turn clockwise for a faster modulation rate.

Amount

This parameter determines to what degree the selected parameter destination will be affected by the LFO 1, i.e. the amount of vibrato, filter wah or auto-panning.

Pitch Bend Range

The Pitch Bend Range parameter sets the amount of pitch bend when the wheel is turned fully up or down. The maximum range is 24 semitones (=up/down 2 Octaves).

Setting number of voices - polyphony

This determines the polyphony, i.e. the number of voices, or slices, Dr. Octo Rex can play simultaneously. For normal loop playback, it is worth noting that slices sometimes “overlap”. Therefore, it is recommended that you use a polyphony setting of about 3-4 voices when playing REX files. If you are “playing” slices via MIDI, the polyphony setting should be set according to how many overlapping slices you want to have.

Note that the Polyphony setting does not “hog” voices. For example, if you are playing a file that has a polyphony setting of ten voices, but the file only uses four voices, this doesn’t mean that you are “wasting” six voices. In other words, the polyphony setting is not something you need to consider if you want to conserve CPU power - it is only the number of voices actually used that counts.

Audio Quality settings

Dr. Octo Rex features two parameters that provide ways of balancing audio quality vs. conservation of computer power. The parameters are called “High Quality Interpolation” and “Low Bandwidth” and are located to the right on the rear panel:

High Quality Interpolation

When High Quality Interpolation is active, the loop file playback is calculated using a more advanced interpolation algorithm. This results in better audio quality, especially for loops with a lot of high frequency content.

•	High Quality Interpolation uses more computer power - if you don’t need it, it’s a good idea to turn it off.

Listen to the loop in a context and determine whether you think this setting makes any difference.

Low Bandwidth

This will remove some high frequency content from the sound, but often this is not noticeable (this is especially true if you have “filtered down” your loop). Activating this mode will save you some extra computer power, if needed.