Newbie question on Oscillators

For discussion of the Voltage Modular synthesis ecosystem.
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anonyrat
Posts: 51
Joined: Sat Sep 04, 2021 1:19 am

Newbie question on Oscillators

Post by anonyrat »

In my quest to learn this beast, I was trying out a simple oscillator. Then when I understood what I was doing, I thought I would substitute it for another one. So I started with the CA Osc, Then the vintage osc and finally the LAB Osc. I was stumped as to why the LAB one was one octave lower. Can someone please explain as this makes no sense to me. Have included the two examples:-
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ColinP
Posts: 939
Joined: Mon Aug 03, 2020 7:46 pm

Re: Newbie question on Oscillators

Post by ColinP »

As far as I can tell the CA Oscillator is an octave too high.

It's all down to a pitch standard based on the length of organ pipes. Personally I think it's a bit daft using such old fashioned terminology.

The relationship is f = v / 2L.

Where f is the frequency in Hz, v the speed of sound in m/s and L the length of the pipe in metres.

Sixteen feet is roughly 4.88 m and the speed of sound is roughly 343 m/s (it depends on temperature and barometric pressure).

So 343 / (2 * 4.88 ) gives us roughly 35.14 Hz which is close to C1 (32.703 Hz).

But the CA Oscillator seems to be producing C2 at 16' with zero CV input.
ColinP
Posts: 939
Joined: Mon Aug 03, 2020 7:46 pm

Re: Newbie question on Oscillators

Post by ColinP »

Out of curiosity I just did a little research and it seems like a foot has varied in length over time, so not a great basis for tuning.

My favourite definition of 16' has to be...
Stand at the door of a church on a Sunday and bid 16 men to stop, tall ones and small ones, as they happen to pass out when the service is finished; then make them put their left feet one behind the other, and the length thus obtained shall be a right and lawful rood to measure and survey the land with, and the 16th part of it shall be the right and lawful foot.
http://www.robweir.com/blog/2007/12/rig ... -rood.html
anonyrat
Posts: 51
Joined: Sat Sep 04, 2021 1:19 am

Re: Newbie question on Oscillators

Post by anonyrat »

Well done Colin, now I'm really confused. Or were you just being rood?

My Shetland pony thinks he is 16 hands high measured with a little girl's hands.

Surely the frequency should be the same no matter what, whether it is hz or ft?
400hz is A and if it is now different then millions of guitar tuners are wrong.
ColinP
Posts: 939
Joined: Mon Aug 03, 2020 7:46 pm

Re: Newbie question on Oscillators

Post by ColinP »

In an ideal world we would all use SI units or C1, C2 etc rather than things like feet or 1/16th roods.

Middle A is now 440 Hz but the standard concert pitch has varied wildly over time. There was a long period of pitch inflation. Ludwig van Beethoven's A tuning fork produced 455.4 Hz so we now hear his work more than a semitone flat. Some other classical works are now played higher in pitch than intended by their composers. It's a mess.

Even today there isn't agreement about what pitch zero volts on the V/Octave scale is.
MRBarton
Posts: 133
Joined: Sat Aug 10, 2019 7:11 pm

Re: Newbie question on Oscillators

Post by MRBarton »

Sorry it's taken me a while to answer this. It's really quite simple. First you have to realize that these are voltage controlled oscillators and the octave switches are merely a convenience. No matter which octave setting you choose, you can still modulate over the oscillator's entire range. The octave range switches (buttons) just step the control voltage in 1v steps internally. There aren't really any 16-foot soft lead pipes in there. Some VCOs (look at the VM2500 oscillators) don't have feet markings, and others have a coarse and fine tune control with no markings at all (Emu modular stuff comes to mind). Moog borrowed the organ pipe feet convention so that users would have a general idea of what to expect from each range. 2' is 2 octaves higher than 8'. It carries no further meaning.

Now the reason the Laboratory VCO sounds one octave lower is by choice. I wanted middle-C (C4) to sound in the 8' range because there is more room to dial down into the lower octaves. If middle-C was in the 16' range at C4, there is only one position to move down before you're in the LFO mode of the oscillator. In other words, middle-C winds up in the middle. That's really it, so don't let it bother or confuse you. There is no standard.

--mb
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