Much like the envelope, the low frequency oscillator (LFO) is a synthesis fundamental utilized for changing sound parameters over time. A LFO is basically the same thing as an audio oscillator, with the biggest difference is that they’re designed to run at a much smaller frequency range. The range is generally below the limits of human hearing, 0Hz to 20Hz. Though many analog and digital LFOs usually oscillate at higher frequencies. There are generally no restrictions for using an audio oscillator as an LFO.
Today’s example uses an LFO to modulate the frequency of a square wave oscillator. I use three different waveforms (triangle, sawtooth, square) so that you can hear how their shapes affect the sound. For example, at the lower frequencies, the triangle wave causes the pitch of the audio to smoothly go up and down while the square produces a trill-like quality.
In the listening example, you’ll hear everything from vibrato, to trills, to classic sci-fi lasers to something straight out of Pac-Man.
Download low_frequency_oscillator.csd here.
I’ve been thoroughly enjoying these blogs: thanks for posting them! Also, I was about to work on adding an LFO to an instrument I was working on and thought I’d mention one can use the lfo opcode:
http://csounds.com/manual/html/lfo.html
it has a number of built-in shapes that make it convenient to use.
@Steven – I completely forgot about the lfo opcode. I may have to revise this blog. Or at least mention it later in another post. Golden advice since I’m trying to reduce these synth fundamentals tutorials to the smallest number of steps possible.
I, too, am enjoying this course. As you are aware, no doubt, there is a lot of material about synthesis on line, but I thought I’d mention Welsh’s ‘Synthesis Cookbook’, which I recently reread. It has some rather nice ‘classic’ algorithms that can be used in csound. It may even give you a few ideas on where to proceed to in your Blog! At any rate, I’ll be sure to keep reading, since your style of presentation ‘resonates’ with how I think too.
@Bob Foose I’ve almost purchased the Welsh book on many occasions. Perhaps it’s time I invest in a copy. In the mean time, I’m going to check out the PDF preview on the website.
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