Most of my stuff is either old-school electromechanical keyboards, for which Genuine Soundware stuff is tops (Organized Trio, mentioned above, is from this company).

http://www.genuinesoundware.com/?a=products

Organized Trio is a freeware, that will eat a little more CPU than the VB3 product from the same company and doesn't have quite all the bells and whistles, but is still WAY better than a sampled organ sound.

Their Rhodes and Wurly emulations are excellent. Very fun to play.

For ambient, washy type stuff, I use a variety of VSTi, preferring Cygnus by Krakli http://www.krakli.co.uk/cygnus.htm and Chameleon 5000 http://www.camelaudio.com/cameleon5000.php Note: Cameleon has been replaced by Alchemy.

The cool thing about both of those synths is that the late, great Tim Conrardy wrote patches for both of them.

Analog lead synth stuff:
http://glenstegner.com/softsynths.html

Orchestral / Acoustic Instruments:

lately I've been using a cut-down version of Garritan Personal Orchestra that came bundled with Tracktion. There's more there than I'll ever make use of what with individual string parts to make my own string sections, etc. The Steinway is nice. It's a little bright for my ear for ambient music, so I've taken to low pass filtering it pretty heavy and sending to a muffly reverb to make it sound more distant. Recent fiddling around example in 6/8 and 7/8 with this piano:
http://rockstarnot.rekkerd.org/fawm2012/Scott%20Lake%20-%20God%20Almighty%20-%20FAWM2012-1.mp3 (Don't blame the terrible drum parts on any program, that's my two-finger on the keyboard attempt - late at night. Will be replaced, hopefully, by a real drummer with a properly mic'ed kit)

See, the thing is, most of my songs really aren't like others here, where autogenerated parts are the norm. I've kind of approached my music making from a different angle, where I have to be able to play everything that gets recorded. This is, admittedly, a limiting mindset. But it does cause one to peek into different corners than most on this forum. For example: I have yet to write a song that uses a horn part; mainly because I just can't hear it correctly in my head to know when and what would be appropriate.

The one exception I have is drum parts - I simply use loops and when I can get a usable output, I'll let Jamstix jam along and print it's output to audio. Jamstix here: http://www.rayzoon.com/ Note, Jamstix's jam-along function doesn't work with PG products.

I'll also use BFD for drums. The version I have came free on a Computer Music magazine cover DVD a few years ago.

Guitars - I do those myself to within my abilities. With electric guitars, this means that I often do textural things rather than lick-based things; though with practice, I can pull off some country licks. Also includes bass. Means that my bass parts will never be mistaken for Mr. Jamerson, or Ms. Kay, or Misters Wooten or Clarke - but it's fun to try to get there!

I use Guitar Rig 3 LE and Amplitube 1 LE for amp simulation, or my trusty Behringer V-Amp2, but that's not a plugin.

I tend to hide in the land of delay and reverb when it comes to guitar textures. Favorite signal chain is:
Amp sim --> Kjaerhus classic filter or Frohmage filter --> Bionic Delay on a tape delay emulation --> Ariesverb reverb.

Locations for those plugins:
http://www.acoustica.com/plugins/vst-directx.htm
http://www.ohmforce.com/HomePage.do# (note - very dodgy website, doesn't work 1/2 of the visits at least, but Frohmage is very fun to play with so it's worth the effort)
http://www.interruptor.ch/vst_overview.shtml
http://www.ariescode.com/index.php (use the freeware version - note that sometimes this thing can be a resource hog and also go into resonance - you've been warned - but the first preset, temple of the ancients, is heaven for ambient music when used as a bussed effect)

It would take years to learn the finer points of this rather small collection of instruments and effects. Have fun!

My Songs, photos, writing,etc.
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