Combining SAW + PULSE

[creativespiral]

I'm finding that pressing both SAW + PULSE, I seem to be getting Two Saws combined together, rather than a Saw and a Pulse.   The Pulse Width seems to just control phase offset of a second saw.   I was hoping to be able to combine a thin pulse with a saw... for those nice buzzy saw sounds.  Also, was expecting an amplitude increase when combining them together.

I don't have a vintage unit on hand to compare to, but just compared with Arturia OP-Xa below...



Tried with both Osc Square Modes.   

Is there a setting I'm missing?  A firmware bug?  Or is this the intended behavior?

[strytten]

Great question. Consider emailing Oberheim support if you haven’t already done so. Eager to hear the outcome.

[deflep44]

Marcus talks about this in this video around 10:20ish. Apparently you couldn't combine waveforms until the OB-8. And on the 8 they decided to offset the phase of the square by 50% so that when combined with the saw it produces those octave up harmonics. Then modulating the pulse brings those in and out almost like a flanger/phaser sound. So very different than what you'd expect if coming from combining waveforms on something like the Prophet 5. But a uniquely oberheim and interesting sound. I think this is partly why there is a different OB8 square volume/mode, as it's a bit lower in volume in order to make them match and this effect sound best.



https://youtu.be/0KuKq-ECU9E

[strytten]

What a great clip, and a great instruction point on the OB X8 programming. I used an OB8 for many years and never fully understood this until now. Thank you so much for this post!

[creativespiral]

Interesting vid...  Thanks for posting.

Just tested a bit further.  The OB-X8 has a falling saw / reverse saw oscillator, and the pulse is low for the first half, phase locked (at 50% duty).  I think Marcus described it opposite in the video (with rising saw), but his point remains. 

In the original OB-8, this must be how their phase relationships of the saw/pulse oscillators were. 

I guess the part that still confuses me a bit is why the amplitude of the saw seems to be attenuated down when the pulse is added...  Is that how the OB-8 VCOs work as well?   

On many other synths, I use this type of phase locked saw+pulse combo, but the relationship between the two waves is usually phase inverted for one of them, which is why I was expecting a different result.   And some others have full 0-100% PWM control, rather than 50-100%.   My preference from a sound design standpoint would be to have the pulse phase inverted when they are combined, but if this is how the OB-8 is configured, I totally get keeping it that way for this recreation.   

If possible via firmware to have a menu option to phase invert the Pulse, that would be feature request of mine -- it would elevate the sound design possibilities.  The thin pulse added to a saw can create a very nice buzzy saw sound, and there's lots of other interesting timbres as you pwm the pulse. 

On the plus side, this current implementation does allow the OB-X8 to create some interesting analog supersaw type of patches.  (by using saw+pulse on both oscillators with detune and pwm, and potentially stacked -- You can get the sound of up to 8 sawtooths per note...   for reference, Roland's Supersaw used seven I believe)   Pseudo analog supersaw.   I created a couple patches last night that sound pretty huge.   

[strytten]

From p. 21 of the manual:

The OB-X provided only Saw and Pulse waves, while the OB-8 added
the Triangle wave, plus the ability to combine Saw and Pulse. The Pulse
wave was also softer on the OB-8 than on the OB-Xa and OB-X. Since
the OB-X8 always allows for the saw and pulse waves to be combined, a
Page 2 feature is provided to select whether the pulse wave’s level should
be that of the OB-8 (required to match OB-8 presets), or the level of the
OB-X or OB-Xa.

[strytten]

And from p. 31 of manual:

The OB-X8 authentically recreates all of the modulation capabilities of
the OB-X, OB-Xa, and OB-8, even though they are quite different. The
OB-X and OB-Xa utilized analog LFOs with analog control of all routing
and modulation amplitude. The OB-8’s LFO was digitally generated
before converting to analog control voltages to send to their destinations.
The OB-X8 has a new Page 2 parameter to select whether the current
preset’s LFO will be from the OB-X/Xa or OB-8.
Several differences occur between the two modes since they represent
very different implementations. The Speed and Depth controls will
behave with different limits and curves, some waveforms have different
shapes (for example, the Sine wave in OB-8 mode is actually a Triangle
wave, since that is what was implemented in the OB-8) and different
phases (the OB-X/Xa square wave is negative-going, while the OB-8 is
positive).

...

The OB-X square wave pitch modulation is mainly negative, while the OB-8
square wave to pitch is positive only. You can set the square wave LFO shape to
match either legacy instrument using the Page 2 LFO Type parameter.

[strytten]

And from p. 50 of the manual, here are a couple "page 2" parameters:

4. Osc 1 Pulse Width: Although the shared pulse width potentiometer
sets the pulse width of both oscillator pulse waves in tandem, this Page 2
parameter allows independent control of Oscillator 1’s pulse width.

5. Osc 2 Pulse Width: As above, this allows independent control of
Oscillator 2’s pulse width, separate from the panel pot.

If you hold the osc 1 pulse Wave switch on page 1 while turning the pulse WIdth
knob, to control only Osc 1’s pulse width. Similarly, holding the Osc 2 pulse Wave
switch while adjusting the pulse WIdth knob will adjust only Osc 2’s pulse width.