Osc 3 as a LFO

Tips and techniques for Minimoog Analog Synthesizers
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DavidC
Posts: 4
Joined: Thu Mar 30, 2006 4:16 am

Osc 3 as a LFO

Post by DavidC » Fri Mar 31, 2006 4:17 am

It seems like the Voyager's implementation of Osc 3 as a LFO is a little more complicated than the same implementation on the Minimoog Model D. The Minimoog Model D offers a single band of LFO frequencies while the Voyager offers 6 bands of LFO frequencies.

If you want to use Osc 3 as a LFO on the Minimoog Model D, you would:
1) Flip the "Osc 3 Control" rocker switch to "off". (Not only does this disable keyboard tracking, it also expands the range of Osc 3's "Frequency" pot from "1 octave" to "6 octaves".)
2) Set the "Osc 3 "Range (or Octave)" selector switch to "Lo". (Setting the "Range (or Octave)" switch to "Lo" specifies a single range of low frequencies that Osc 3's "Frequency" pot can select from.)
3) Tune in the desired frequency using Osc 3's "Frequency" pot.

On the otherhand, if you wish to use Osc 3 as a LFO on the Voyager:
1) Flip the "3 KB Cont" rocker switch to off. (Disables keyboard tracking of Osc 3 and expands the range of Osc 3's "Frequency" pot.)
2) Set the "3 Freq" rocker switch to "Lo" (Configures Osc 3 as an LFO as opposed to an audio oscillator)
3) Select one of 6 low frequency bands using the "Octave (Range)" selector switch (32', 16', 8', 4', 2', 1')
4) Tune in the desired frequency using Osc 3's "Frequency" pot.

Does anybody know if there is a technical spec that specifies the low frequency range for each of the 6 low frequency bands (32', 16', 8', 4', 2', 1'). If not, perhaps somebody has measured the frequency range of each band using a frequency counter.

I have made some rough estimates of various values within each of the 6 ranges by making audible comparisons with the existing LFO. Although I don't claim that they are very accurate, I'll post some of these values (below) in order to facilitate discussion on this matter. Hopfefully, somebody will post factory specifications or actual measurements for the entire range of each band.

32': 0.2 Hz (-4.5*); 0.8 Hz (0); 3 Hz (+7)
16': 0.4 Hz (-6); 1.3 Hz (0); 3 Hz (+4); 5.5 Hz (+7)
8': 0.6 Hz (-7); 3 Hz (+1); 10 Hz (+7)
4': 1.2 Hz (-7); 3 Hz (-1); 12 Hz (+4.5)
2': 2.25 Hz (-7); 6 Hz (-1); 12 Hz (+2)
1': 3.5 Hz (-7); 12 Hz (-1); 25 Hz (+1)

*Note that the value in parenthesis is the dial position for Osc 3's frequency pot using the scale written on the front panel of the Voyager.

The advantage of having 6 frequency bands as opposed to a single frequency band is it increases the resolution of the Osc 3 Freq pot for the entire low frequency range. However, one observation that is readily apparent from the estimates above is that there is considerable (if not excessive) overlap between adjacent bands. For example, when comparing the 16' and 32' ranges, the 16' range only expands the maximum frequency range from 3 Hz to 5.5 Hz. This corresponds to about 20% of the frequency pot's range: dial positions +4 through +7 for the 16' range.
David

EricK
Posts: 5972
Joined: Fri Apr 09, 2004 2:09 pm

Post by EricK » Mon Apr 03, 2006 11:15 pm

I first ran across this when i used the effect "Panning Throbber" I noticed that there was something going on and i learned how to control the 3 osc respectively.

I can't figure out how they made it pan though.

I am trying to stack my modulation like using osc 3 like you describe, with 1 sample and hold routed to the osc 3 waveshape and a second to a different oscilator or to the filter.

Im trying to have 3 seperate tempos going.

I learn a little more about my voyager all the time.
EricK

THanks for the tips.
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GregAE
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Post by GregAE » Tue Apr 04, 2006 7:27 am

EricK wrote:I first ran across this when i used the effect "Panning Throbber" I noticed that there was something going on and i learned how to control the 3 osc respectively.

I can't figure out how they made it pan though.

Im trying to have 3 seperate tempos going.


'Panning Thobber' (Zon Vern Pyles bank, #33) uses the LFO triangle to control panning through the Mod Bus. Oscillator 3 is used as a second LFO, controlling the filter cutoff (this is the 'throb' effect).

While it may be possible to generate 3 separate tempos through some clever programming trick, it would be much easier to add a third LFO (from the CP-251 or MoogerFooger for instance) to affect another parameter, such as Waveform.


Greg
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