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 << prev Oberheim OB-Xa (-obxa) (1980) next >>

This is almost two OB-X in a single unit. With one keyboard they could provide
the same sounds but with added voicing for split/layers/poly options. The OB-Xa
did at least work with all 10 voices, had a single keyboard, and is renound for
the sounds of van Halen 'Jump' and Stranglers 'Strange Little Girl'. The sound
had the capability to cut through a mix to upstage even guitar solo's. Oberheim
went on to make the most over the top analogue synths before the cut price
alternatives and the age of the DX overcame them.

Parameters are much the same as the OB-X as the algorithm shares the same code,
with a few changes to the mod routing. The main changes will be in the use of
Poly/Split/Layer controllers for splitting the keyboard and layering the sounds
of the two integrated synthesisers and the choice of filter algorithm.

The voice controls apply to the layer being viewed, selected from the D/U


    Auto: autotune the oscillators
    Hold: disable note off
    Reset: fast decay to zero for envelopes, disregards release parameter.
    Master Tune: up/down one semitone both oscillators.


    Glide: up to 30 seconds
    Oscillator 2 detune: Up/down one semitone

    Unison: gang all voices to a single 'fat' monophonic synthesiser.


    LFO: rate of oscillation
    Waveform: Sine/Square/Sample&Hold of noise src. Triangle if none selected.

    Depth: Amount of LFO going to:
        Freq Osc-1
        Freq Osc-2
        Filter Cutoff

    PWM: Amount of LFO going to:
        PWM Osc-1
        PWM Osc-2


    Freq1: 32' to 1' in octave increments.
    PulseWidth: Width of pulse wave (*).
    Freq2: 16' to 1' in semitone increments.

    Saw: sawtooth waveform Osc-1 (**)
    Puls: Pulse waveform Osc-1

    Env: Application of Filter env to frequency
    Sync: Osc-2 sync to Osc-1

    Saw: sawtooth waveform Osc-2
    Puls: Pulse waveform Osc-2

    * Although this is a single controller it acts independently on each of the
    oscillators - the most recent to have its square wave selected will be
    affected by this parameter allowing each oscillator to have a different
    pulse width, as per the original design.

    ** If no waveform is selected then a triangle is generated.


    Freq: cutoff frequency
    Resonance: emphasis (*)
    Mod: Amount of modulation to filter cutoff (**)

    Osc-1: Osc-1 to cutoff at full swing.
    KDB: Keyboard tracking of cutoff.

    Half/Full: Oscillator 2 to Cutoff at defined levels (***)

    Noise: to Cutoff at defined levels
    4 Pole: Select 2 pole or 4 pole filter

    * In contrast to the original, this filter will self oscillate.

    ** The original had this parameter for the envelope level only, not the
    other modifiers. Due to the filter implementation here it affects total
    depth of the sum of the mods.

    *** These are not mutually exclusive. The 'Half' button gives about 1/4,
     the 'Full' button full, and both on gives 1/2. They could be made mutually
    exclusive, but the same effect can be generated with a little more flexibity    here.

Envelopes: One each for filter and amplifier.


Mode selection:

    Poly: play one key from each layer alternatively for 10 voices
    Split: Split the keyboard. The next keypress specifies split point
    Layer: Layer each voice on top each other.

    D/U: Select upper and lower layers for editing.

Modifier Panel:

    Rate: Second LFO frequency
    Depth: Second LFO gain
    Low: Modifiers will affect the lower layer
    Up: Modifiers will affect the upper layer
    Multi: Each voice will implement its own LFO
    Copy: Copy lower layer to upper layer

    Mod 01: Modify Osc-1 in given layer
    Mod 02: Modify Osc-2 in given layer
    PW: Moduify Pulse Width
    AMT: Amount (ie, depth) of mods and freq wheels

    Transpose: Up or Down one octave.

The oscillators appear rather restricted at first sight, but the parametrics
allow for a very rich and cutting sound.

The Copy function on the Mod Panel is to make Poly programming easier - generate
the desired sound and then copy the complete parameter set for poly operation.
It can also be used more subtely, as the copy operation does not affect balance
or detune, so sounds can be copied and immediately panned slightly out of tune
to generate natural width in a patch. This is not per the original instrument
that had an arpeggiator on the mod panel.

Sample sounds in OGG format. As with most of the samples these were played from
my qwerty keyboard so there is a rather slow response and no velocity sensitivity.

    Sample #1: first memory, two layered sounds, mild detune, subtle panning.

Bristol is in no way associated with the original manufacturer, neither do they endorse this product.

Bristol is free software. Bristol carries no logo.

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