http://soundcloud.com/foolsgoldrecs/giraffage-chocolate starts on 0.49


http://soundcloud.com/wave-racer/foster-the-people-best-friend-wave-racer-remix starts at the beginning of the song.

i hear this sound a lot. sounds like a wah effect or something on the synth, not sure. could it be the op1 as well?

any help?

 

Ask Baxter, he will know. To me it sounds like it is just a phase shifter.

 

Filter envelope.
You set an envelope to control a filter cutoff, to start sweeping when you press the key (note-on). Then with filter envelope attack, decay, sustain, decay (and amount, range, etc) you decide how the sweep will behave.
There are different filter types, but start with low-pass filter envelope. Then try highpass...bandpass, etc.

It can also be "auto-wah", i.e filter cutoff controlled by the amplitude/volume of the synth coming into the auto-wah.
http://usfiles.brothersoft.com/mp3_audio/misc_plug-ins/classic_auto-filter_v101.zip (free VST, PC)