Hobbes Audio Path

1. Oscillators

The oscillator panel provides control of up to four polyphonic oscillators, a suboscillator, and global pitch, as described below.

1.1. Oscillator Waveforms

In the top left corner, the Osc1 through Osc4 switches select the waveform for the respective oscillator. All oscillators may be disabled to save CPU.

1.1.1. Ring Modulation

Various ring modulations are available instead of oscillators 3 and 4. For example, selecting "2*3" for osc4 provides ring modulation of oscillator 2 and 3, instead of a separate oscillator for osc4.

1.1.2. Waveset Oscillators

1.1.3. Bang oscillators

The bang oscillators (1!*2!, etc.) are the oscillator sources multiplied by themselves, then added together (1*1 + 2*2), which provides rich metallic harmonics.

1.1.4. Mirror Oscillators

When the raw oscillator output exceeds the contour level, the output is mirrored once around the contour level.

The mirror may be positive or negative. If contour is positive, then the oscillator waveform is mirrored down. If contour is negative, then the oscillator waveform is mirrored up. Note that polyphonic modulations can create different waveforms for each voice.

1.1.5. Staircase Oscillator

At contour of zero, the staircase is simple rising step waveform from -1 to +1. Contour modulates the height of intermediate steps to distort the staircase into random steps.

1.1.6. Ziggurat Oscillator

This is a rising and falling staircase. The contour modulates the height of intermediate steps to make complex waveforms.

1.1.7. Fishtail Oscillator

This is a series of rising and falling ramps in the shape of a fishtail. Contour modulation adjusts the slope of the ramps.

1.1.8. Effects Modes

1.2. Global Pitch

The global pitch controls provide for pitch offset and pitch modulation for the entire synthesizer. Pitch tracking can be scaled around a settable center pitch (with the center pitch value displayed under the center knob). Middle C is displayed as C5. If set to middle C, pitch tracking is uniform across the entire pitch range. Higher and lower settings skew pitch above and below the center pitch accordingly.

1.2.1. Tempo Glide

Tempo glide (portamento) may be applied to the global pitch. The portamento is polyphonic. When enabled, the pitch slowly and uniformly moved to the pitch of a newly received note from the pitch of the last received note. The glide rate is a fixed period, no matter what the note pitches are for the current and last note.

Tempo

The glide rate is set by this panel's tempo control here, with the clock period derived from the global clock settings.

Gliss . When enabled, the output is glissando instead of portamento. The glide moves between fixed semitone intervals (as fast glide rates the difference may not be audible).

Enable

Selects a modulation source which enables or disables glide. The modulation source is sampled once for each note, when the note-on event is received.

Fix

When disabled, glide duration changes, depending on the level of the modulation source when a note starts. When enabled, the glide duration is exactly that set by tempo when the modulation source is above zero. Glide is disabled when the source is zero or below.

1.3. Oscillator Controls

For all oscillator XY panels, the vertical axis controls and displays oscillator contour. Values are displayed as rectangles. One corner of the rectangle shows values before modulation; the opposite corner shows values after modulation.

For oscillator 1 and 3, the horizontal axis controls and displays soft sync. For oscillator 2, the horizontal axis controls the suboscillator volume.

1.3.1. Osc1

The XY panel for Osc1 controls the contour vertically, and soft sync horizontally.

Pitch

Oscillator 1 simply uses the global pitch, and doesn't have its own pitch modulation controls.

Soft Sync

On Osc1 and osc3, soft sync is available for all waveforms. Soft sync is provided by inverting osc1/3 when the sync source crosses a threshold. The base threshold is set by the X value of the respective oscillator's XY panel.

• A switch next to the Osc1 sync modulation controls can turn off soft sync, to reduce CPU utilization. If the switch is on, then the sync list box selects the oscillator from which soft sync is derived.
• The level of the sync source at which inversion occurs can be set and modulated independently for osc1 and osc3.

FM

If the oscillator is an FM oscillator, this selects the audio source used for FM modulation. For all the oscillators, any of the other oscillators or the suboscillator is available as an FM source. For Osc1 and Osc3, additional FM sources are the morph mixers, the filters, and the envelopes (with high gate level fixed at 1.0).

1.3.2. Osc2

The XY panel for Osc1 controls the contour vertically, and the level of a suboscillator horizontally. Osc2 also has its own pitch modulation controls.

Pitch

Oscillator 2 has its own pitch modulation controls, which generate a pitch offset from the global pitch for each voice. After applying the pitch offset, the oscillator pitch can optionally be forced to the same key scale as for global pitch, by enabling the oscillator's dedicated track button.

Suboscillator

A switch next to the contour controls for osc2 enables or disables the suboscillator. The suboscillator is derived from audio processing circuits for the Osc1 sync. (Typically, osc2 would be used for osc1 sync, although this isn't required). If osc1 sync is enabled, then there is no CPU overhead for enabling the suboscillator.

1.3.3. Osc3

The XY panel for Osc1 controls the contour vertically, and soft sync horizontally. Osc3 also has its own pitch modulation controls.

Pitch

Oscillator 3 has its own pitch modulation controls. They operate the same as for oscillator 2.

Soft Sync

The soft sync switch, list box, and modulation controls have the same effect as for osc1. If soft sync is disabled, then the sync modulation panel is still available as a complex modulation source throughout the instrument.

FM

Same as for Osc1 FM.

1.3.4. Osc4

Although it has no XY panel (to save screen real estate), a separate waveform can be selected for oscillator 4.

Pitch

The Psrc knob sets whence Osc4 derives its base pitch. If Psrc is 1, then pitch is derived from the global pitch. If Psrc is 2 or 3, then pitch derives from oscillator 2 or 3, respectively. You can also set Psrc to fractional values up to 4.0, in which case base pitch is a mix of other pitches. for example, if Psrc is 2.5, then the base pitch of osc4 base is half way between the pitches of osc2 and osc3. If Psrc is half way between 3 and 4, then pitch is half way between the pitch of oscillator 3 and global pitch.

The oct and P knobs add an offset to the base pitch determined from the setting of Psrc .

The scale button, when enabled, causes the derived pitch to be forced to the key scale.

Contour

The CntrlSrc knob sets whereosc4 derives contour and modulation, in the same way as the Psrc knob works for Osc4 pitch. The offset knob adds a fixed offset to the contour value derived from the CntrlSrc knob. The gain knob scales the result of adding the value from the contour source and the offset knob. The range and clip is applied to the result of the gain calculation.

FM

Same as for Osc1 FM.

The vector mixer provides modulated mixing for each of four audio sources. The upper mixer feeds filter 1 input. The lower feeds filter 2 input. The vector mixer outputs are also available as FM sources elsewhere in the instrument.

The design is similar to the joystick control on the Korg Wavestation. The XY panel and modulations effect a four-way crossfade between the oscillators, with one oscillator in each corner, as follows:

For example, if all oscillators are enabled:

• When the mix is in the top left corner,
  only oscillator 1 is output.
• Moving right:
  oscillators 1 and 2 decrease;
  oscillators 3 and 4 increase.
• Moving down:
  oscillators 1 and 3 decrease;
  oscillators 2 and 4 increase.

When the mix is in the center of the XY panel, and there is no overdrive being applied, then there is an equal mix of all four oscillators.

As well as a complete set of standard modulation controls, each mixer has one enable button for each oscillator, and an overdrive sub-panel.

1.4. Enabling Oscillators

The buttons around each corner of the XY panel enable the the respective oscillator; if a button is off, then the morph mixer produces no sound for that voice when that voice's mix point is in the corresponding corner. The enable button overrides all other mixer settings.

The button is fully debounced and does not cause any clicks when changed.

1.5. Oscillator Overdrive

There are four knobs for each vector mixer, one knob for each oscillator. The knobs are arranged in a square, with each oscillator in the same corner as for the XY panel.

Each knob controls the overall maximum drive of the respective oscillator (if the oscillator is enabled, as described above).

When the crosshair for any voice is in the corresponding corner of the XY panel (and the oscillator is enabled for that corner), then the output amplitude of that oscillator will be exactly as set by the oscillator's overdrive knob. Moving away from that corer, the amplitude gradually decreases for that oscillator; when the crosshair is on the other side of the panel, the oscillator is inaudible.

The instrument includes automatic gain compensation on outputs, so that changing an oscillator's overdrive setting changes the overdrive fed into the filter, but does not generally change the overall output volume. However, more extreme filter settings may still cause some variation in volume, in which case the polyphonic limiter for that filter output may be engaged.

1.5.1. Oscillator Level Display

The XY panels also display the current morph point for each voice with a rectangle. One corner of the rectangle shows the oscillator mix before modulation; the opposite corner shows the oscillator mix point after modulation.

The value meters for the vector mixers are slightly different from the other XY panels. For each vector mixer, there are four value displays, two above and two below the XY panel. By default each value meter shows the current level of the oscillator for the corresponding corner (after overdrive). Otherwise, the value meters behave the same as for other XY panels.

2. Dual Filter

2.1. Filter 1

The filter XY panel displays rectangles for each active voice. As well as standard modulation controls, the sub-panel for Filter 1 also contains the following additional features:

2.1.1. Frequency Modulation

The F slider sets the amount of frequency modulation (FM depth is scaled in semitones). Next to the FM slider is a list box to select the FM source. Note this list box is actually a switch (to save CPU) and changing its setting may interrupt the sound.

Envelope 1 (A1) envelope 2 (A2) are also available here. These audio-rate envelopes can be preferable over event-rate envelopes, for higher quality sound. The audio-rate envelopes use a fixed gate level of 1.0.

2.1.2. Logarithmic Resonance

When on, the Exp button (by the resonance Gain knob) causes the amount of resonance change to flatten out as resonance approaches 1.0.

When off, resonance increases linearly with increasing values.

2.1.3. Pitch Track Center

Pitch tracking for both cutoff and resonance can be scaled around a different center pitch than for the rest of the instrument. The center knob controls the center pitch for pitch tracking, and the note name is displayed below it.

2.1.4. Filter Type Selection

The top right corner contains switches to select filter type. Be aware these are switches are will interrupt the sound:

Filter 1

Selects filter type between one of 20 filter types, including EQ and comb filters, as shown in the following table.

Filter 1 Types

Sat

Switch to enable post-filter saturation for filter 1.

F1>F2 Feed

Switch to selects whether filter 1 output is sent to filter 2, with or without saturation.

F2 Group

Switch to select the group of filters which are available for filter 2 morph. The groups are Low Pass (L2b, L4, B2, BL4, B4, H2, and bypass), High Pass (B2, BH4, B4, H2, H4, and bypass) and Ladder (Ld1, Ld2, Ld3, Ld4, and bypass).

Sat2

Switch to enable post-filter saturation for filter 2.

2.2. Feed and Morph

The middle XY control in the filter panel controls F1>F2 feed (vertically) and filter morph (horizontally). Feed and morph have standard modulation controls, with the following additional features and characteristics.

2.2.1. Filter 2 Feed

When the value for any particular voice is at the bottom of the XY display, then there is no feed from filter 1 to filter 2 for that voice. When in the middle of the XY panel, then the filter feed is unity gain (1.0).

Above the middle point, the filter feed is overdriven for that voice. Note that saturation can be independently enabled for filter 1 and F1>F2 feed, so for example, you can mix unsaturated filter 1 output with saturated filter feed.

2.2.2. Filter 2 Morph

The horizontal axis of the Morph subpanel sets the base morph point for filter 2. the XY panel displays the current morph point for each active voice.

The filter 2 output is a mix of two out or three filter types, controlled by a subpanel in the lower right quadrant of the feed/morph panel.

Here there are sets of three controls labelled Left , Center , and Right . These controls the filter type and drive across the horizontal axis of the XY control.

• When on the left edge, only the left filter type is output. Moving right, the output level of the left filter type gradually decreases, and output of the center filter type increases.
• When in the center of the XY panel, only the center filter type can be heard. Moving from center to right, the center filter type decreases and the right filter type increases.
• On the right edge, on the right filter type can be heard.

Filter Morph Types

The left , cntrl , and right knobs provide switchless selection of the left, center, and right filter types. When you rotate the knobs, the name of the selected type is shown below. Note the F2 Group switch, described earlier, lets you select between groups of available filter types.

Filter Overdrive

Each of the three filter types may be overdriven independently of the others, so you can morph between any levels of filter drive. The instrument automatically compensates for changes in gain internally, so that changes in drive level effect tone, but not output volume.

2.3. Filter 2

As well as standard modulation controls, the sub-panel for Filter 2 contains the following additional features:

• Frequency modulation (F), same as for filter 1.
• Independent pitch track centering, same as for filter 1.
• Logarithmic resonance, same as for filter 1.

3. Output and Effects

3.1. Output Panel

3.1.1. Level

To conserve screen real estate, the level sliders and mute buttons control the filter outputs ( prior to pan and effects). The metering and peak indicators are for final output of the left and right channels ( after pan and effects).

F1 and F2

The F1 and F2 sliders set the output level of each filter before they are fed into pan and the effects chain.

Output Metering

A special low-CPU design displays final output levels of Left and Right channels.

Peak

The box at the top of the metering segments illuminates red for half a second when the final output signal exceeds 0db within the prior half-second period. Also, the actual value of the highest signal level, in any half-second period, is displayed below the meter segments.

Mute

These buttons mute filter 1 and filter 2, respectively. Mute is fully debounced and doesn't cause any clicks.

3.1.2. Pan

There is stereo., polyphonic pan with independent modulation for each filter output.

Pan Slider

The pan slider sets the base pan position for both filter outputs.

Pan Modulation Source

The list box permits selection of 32 different modulation sources.

Pan Modulation Amount

Moving the crosshair in the XY strip horizontally controls the pan modulation amount. The vertical position has no effect. The XY strip additionally displays the current pan position for each voice.

Clp

When enabled, modulations exceeding far left/right are clipped; otherwise, they are mirrored.

3.1.3. Limit

There is independent polyphonic limiting of filter 1 and filter 2, after level setting by the F1 and F2 sliders. With polyphonic limiting, one voice may be limited (due to high resonance values) without affecting the gain of other voices (for which the ADSR envelopes may be at lower levels).

L1 and L2

Enable limiting for filter 1 and filter 2, independently of each other.

Thrsh

Sets the threshold (in dB) for both limiters.

Relse

Sets the release (in milliseconds) for both limiters.

3.2. Effects

The effect chain is:

pan> flange > chorus > echo > reverb.

Each effect has power switches. This lets each effects be individually disabled, to reduce CPU usage, but enabling or disabling the effects interrupts the sound. If you want a snap to enable an effect without clicks, use the Mix knobs in each effect.

3.2.1. Tempo Delay

The instrument includes low-CPU dual delay lines with cross feedback, delay time modulation, and panpot. Input to the delay lines are the mixed filter 1 and filter 2 outputs, after pan and pan modulation.

There are switches to enable and disable the two effect lines separately.

Tempo L and Tempo R

Sets the tempo for each delay line, with time derived from the global clock.

FbL and FbR

Sets the feedback for each delay line.

Pan

Sets the pan position for the stereo output. In its center position, the left delay line is fully left and the right delay line is fully right. Moving the pan position left or right causes one of the delay outputs to be moved towards the center of the stereo field.

Mix

Sets the mix of dry and wet signals. When centered, the mix is equal. When fully left, only the dry signal is heard. When fully right, only the echo output is heard.

3.2.2. Flange

The stereo flange is a CPU-reduced version of the Reaktor 3 stereo flange instrument.

Rate

Sets the rate of delay modulation.

Deep

Sets the depth of delay modulation.

Fbk

Sets the amount of feedback.

Dlay

Sets the base delay prior to modulation.

Mix

Sets the mix of dry and wet signals. When centered, the mix is equal. When fully left, only the dry signal is heard. When fully right, only the echo output is heard.

3.2.3. Chorus

The chorus is a CPU-reduced version of the quad chorus from the REaktor 3 library.

rate

Sets the rate of delay modulation.

sprd

Sets the mount that delay modulation is different across the four delay lines.

deep

Sets the amount that delay modulation affects the delay.

dlay

Sets the base delay amount across the four delay lines, prior to modulation.

Mix

Sets the mix of dry and wet signals. When centered, the mix is equal. When fully left, only the dry signal is heard. When fully right, only the echo output is heard.

3.2.4. Reverb

The reverb is a low-CPU, mono reverb with room size, softness, and diffusion control.

size

Sets the diffusion delay.

diff

Sets the amount of diffusion.

soft

Sets the amount of diffusion modulation.

mix

Sets the mix of dry and wet signals. When centered, the mix is equal. When fully left, only the dry signal is heard. When fully right, only the echo output is heard.

hall

Enables an additional diffusion module with a long diffusion delay, increasing CPUY usage but improving perceived reverb depth.