On a traditional synth, LFO to pitch will retain the root note and play higher pitches based on how much amount you give it. The voltage is added to the root note voltage. Thus if you are playing with other instruments, you can stay in key and use the LFO to trill. The vibrato on the MiniBrute works like this.I agree that this would be a desirable option to have.
However, I'd like to know which traditional synths you have used that have an LFO that works like this. I've played, programmed, and owned many synths over the last three decades and all of them have had the bipolar LFO as standard, while very few even offered the option of setting the LFO to provide positive-only or negative-only modulation.
Well that explains it. The dumbed down LFO phenomenon started to occur about 3 decades ago. Fortunately, I've been playing synths for 4 decades.
(I kid, I kid, but sadly yes I'm getting that old.)
I just did a quick audition. That was 2 hours ago. These things are addictive.
Ok, except where noted, I'm using a square wave on the LFO to trill the oscillator. Positive only preserves the root pitch, and the LFO plays an interval higher than root. If the LFO acts bipolar, the root disappears.
Start off around mid seventies.
Octave The Cat LFO to pitch works as I described (positive only).
Jump 5 years.
The Realistic MG-1 LFO to pitch works positive only. I suspect its cousins the Rouge & Liberation work the same way. Maybe someone with a MiniMg can chime in.
Fast forward about 5 years.
Juno 60 and SH-101 both have bipolar LFO when routed to pitch. The Juno only has a triangle as the LFO wave. The SH-101 is more versatile in waves and faster.
Sequential Circuits SixTrak is positive only. LFO speeds have been compromised at this point.
Casio CZ series digital poly synths work positive only, but the LFO has been renamed vibrato, as it can't be routed elsewhere than oscillator pitch. Other than 4 waves, not much going for it as it's also slow.
Go to one of the last poly synths with analog filters, the Ensoniq ESQ1 & SQ80 circa late 80's, can offset the LFO pitch positive or negative, but the LFO is likely in software at this point. Speeds also have slowed down.
After that, I suspect that bipolar LFOs to pitch became more common, but so did digital synths. Seems like with the advent of digital synths without a VCO/DCO and/or analog filters, the role of the LFO as a necessary tool for sound mangling fell by the wayside.