This sound is a unison patch with the modulation LFO set to Sample and Hold going to the filter cut off.
Oberheim OB-Xa Analog Synthesizer
Above is a picture of an Oberheim OB-Xa 8 voice synthesizer.
Oberheim OB-Xa Analog Synthesizer Sounds
The second sound is another Sample and Hold sound that creates some blurpiness with a long decay
Oberheim OB-Xa Analog Synthesizer Pictures
The far left side of controls of the Oberheim OB-Xa.
The AUTO button on the left Auto Tunes the OB-Xa. Let the Unit warm up
5-10 minutes then press AUTO button so it's tuned to running temp.
The extra modulation controls next to the keyboard of the Oberheim OB-Xa
Above: The keyboard control section and the Main Modulation section
Basically you get an oscillator LFO (low frequency oscillator) that can be
Sine wave, a square wave, or a sample and hold version of a sine wave.
These can be routed to the Frequency Column with OSC1 OSC2 and Filter
switches. The depth sets the level of the modulation
The LFO can also be routed to the Pulse width of the oscillators, again
depth setting the level of LFO
