Switching LFOs... Info, please

[ExpAnonColin]

Someone want to point me in the direction of a good place to read about switching LFOs?  Or, just give me a bit of info... I know little.
Thanks.
-Colin

[R.G.]

Switching how? Switching between waveforms, or digitally-generated waveforms?

There's some info on that at  GEO. Look at "Pseudorandom LFO's" which also covers some direct digital generation.

[ExpAnonColin]

No no, I meant in place of a switch or pot, a la panning.

I couldn't find anything on GEO.

[R.G.]

The trick there is to use a voltage controlled amplifier or attenuator per LFO, and generate both true and inverted LFO waveforms. Feed one to one VCA, the reverse to the other VCA, and then the outputs of the VCAs. Presto - panning with sine or triangle LFO waves, ping/pong with square waves.

By the way, this is fairly tricky to do. I've been trying to get a simple, yet high performance scheme for this designed for at least a few years. You're right, it's not there on the GEO website.

R.G.

[danngreen]

Here's the 4ms panneur schematic.

http://commonsound.com/panneur/panneurscheme.gif

It actually has 2 LFOs, but if the "sync/unsync" switch is set to "sync", then only one LFO is used (the top LFO in the schematic), and you can get stereo panning.
Like RG says, the true LFO signal is split, to drive LED/CdS "A" (top) and also to be inverted and drive LED/CdS "B" (bottom).
Use the waveshaping pot to blend between triangle panning and square-wave ping/pong.

Note that the bottom signal is only inverted if the "Trem/Pan" switch is set to "pan", because the LFO signal is sent to the inverting input of the op-amp. When it's set to "trem", the LFO signal goes through the non-inverting input (and then you get stereo tremolo, with independant depth and gain controls).

This basic design can be used to control all sorts of things, by replacing a resistance in a circuit with the CdS cell(s). Just make sure to use a CdS cell that's matched for the range of resistance you want.[/url]