The Noise Generator adds unpitched audio (noise) into the audio path as an input to the Audio Mixer. You can use noise to add grit and grime, create sound effects like wind and surf, or define the character of the signal being created by the Sample and Hold.
Since the amount of noise is set and modulated in the Mixer, this switch simply selects the color of the noise.
While noise does contain a mixture of all frequencies at once, it's often useful (from an engineering standpoint or a musical/aesthetic one) to adjust the balance between low and high frequencies, accentuating one or the other. We describe the frequency balance of noise by assigning it a color.
White noise is an equal mixture of all frequencies. Pink noise has its frequency balance shifted slightly toward the lows, producing a less "hissy" noise that works well with the human ear. These two types of noise were and are the most popular for electronic music applications, and nearly every analog synthesizer will offer one, the other, or a choice of both, as the original Odyssey did.
ODC 2800 takes the options a bit farther. Violet noise has a strong emphasis on high frequencies, with very little low-end content at all. Conversely, brown noise is almost all low frequencies. A fifth option, red noise (with a tonal balance between pink and brown), is available as a control source in the Assign modulation menu.
Portamento (or glide) is the slow change of pitch between two notes when one is played after the other. For example, if a violinist plays a note, moves their hand to a new position, then plays another note, there is no portamento. Contrariwise, if a violinist plays a note while sliding their hand up or down the neck, the shifting pitch is what we'd call portamento.
Amount: The time for ODC 2800 to change pitch from one note to the next. This setting ranges from 0.00 ms to 2000 ms (two seconds). The time remains constant for narrow or wide pitch intervals, so a glide of 3 semitones will take the same amount of time as a glide of 2 octaves. The latter glide will cover a lot more pitch difference in the same time, so it will sound "faster".
VCO-2 Delay and VCO-3 Delay: These settings slow down the portamento for VCO 2 and VCO 3. This produces the effect of VCO 1 jumping between pitches at the set Amount, with VCO 2 and VCO 3 slowly moving to "catch up". Large VCO Delay amounts can stretch the total time for a pitch shift to 45 seconds or more.
One thing to note about ODC 2800's portamento: it's "smart", an innovation used on Yamaha's famed CS-80 polyphonic synthesizer. When you play a note and then another note, the previous note's pitch is assigned to the new voice before the portamento begins, so the glide sounds very natural as you play, with glide between notes and chords feeling very natural. On other polysynths, once a note was released, the voice card would sit at that note and glide from there when it was next played – which might have been five notes earlier (on a 6-voice synth) or even more! When that happened, glides would be flying in all directions with no apparent pattern to them, making for a random and messy sound.
TL;DR – ODC 2800 doesn't do that. Try it for yourself, by playing a chord with one hand and a melody with the other.
And if you're wondering how this "smart" portamento relates to authentic ARP polyphonic synthesizers? Well, remember that ARP never made one. (The Chroma doesn't count – it was still a nonworking prototype when ARP shut down.) Since there's no historical precedent for polyphonic portamento in an ARP synthesizer, we figured we could put in any kind of portamento we wanted... and we thought this one was really slick. So there you go.
Transpose- This switch is straight off the original Odyssey. Flicking it to jump up or down by 2 octaves while playing was and is a common soloing trick. Map it to a MIDI controller to make it available to your playing technique!