novice and the oscillator

[harry bissell]

There is more to the story... The sawtooth oscillator is called a relaxation
oscillator, because the charge builds up...up...up ... then (ahhh) relaxes.

I don't agree about the triangle wave... It has the same odd-only harmonics as
the (50%) square wave but they fall off at higher frequencies at twice the rate.

Dan: (et al) the triangle can be made by integrating the square wave... but it
isn't practical as you mentioned. If you have a sawtooth wave you can just full
wave rectify it and you will get a triangle. You remove the DC component, and
amplify by two. This is done all the time...

There are also oscillators that integrate an input current until a high limit is
reached, and then reverse the direction of current until a low limit is reached.
This generates a triangle wave directly. It is also easy to make a sawtooth from
a triangle...

The triangle is especially useful for modulation (low frequencies). It can be
converted to a sine wave easily. The triangle and sine waves may not be
"interesting" when filtered but for FM modualtion (vibrato), ring modulation,
amplitude modulation (tremolo) they are essential and should not be overlooked.

I think the reference to "waveform city" ref. to Grant Richter and the "Wiard"
(wired) synthesizer company. He's a list member...

In closing LONG LIVE THE TRIANGLE !!!

thanks... I'm done now.  :^) Harry

Daniel Gendreau wrote:

> The basic concept of most VCOs is based on a simple saw tooth oscillator
> controlled by an input signal called a CV (Control Voltage). A standard CV
> usually represents 1Volt per octave of pitch. The saw tooth oscillator will
> sweep linearly upwards from something like 0V to 5V. When it reaches 5V, it
> snaps back to 0V and continues. The input CV determines the rate at which
> the VCO saws upward and thus the frequency of the VCO.
>
> >From there, you can use a simple opamp comparator (comparing at 2.5V) to
> convert the saw tooth waveform to a square wave. When the saw is below 2.5V,
> the comparator outputs 0V, and when its above 2.5v, the comparator outputs
> 5V. Optionally, some VCOs allow you to adjust this compare point which
> changes the duty cycle of the square wave, also known as Pulse Width
> Modulation.
>
> These are generally the 2 simplest waveforms to generate using analog
> circuits.
>
> >From there, you can use flipflops on the square wave to generate 1/2 and 1/4
> frequency square waves called Sub oscillators. These can be used in
> different proportions to add more bass harmonics to a waveform.
>
> You can also use an opamp integrator circuit on the square wave to generate
> a triangle wave, but the problem here is that the amplitude of this triangle
> wave is inversely proportional to the VCO frequency. I think you have to use
> some sort of compressor circuit which tracks the amplitude of the triangle
> wave and adjusts its gain so the output is always 0V to +5V. Most synths do
> not go to all this trouble because a triangle wave is not very rich in
> harmonic content as compared to the Saw and square waves. IMHO, Its very
> similar in sound to a sine wave and does not filter very well.
>
> I have also seen an exotic scheme which uses an ADC to sample a VCO saw
> waveform, look up the sampled value in a ROM chip and then use a DAC to
> output the analog value from the ROM. This allows you to generate very
> complex waveforms using a simple saw oscillator. I believe it was called
> waveform city, but I cant remember the site I saw it on... Anyone?
>
> Check out some of the Synth-DIY web sites and especially Tom G's site from
> some good projects to experiment with.
> http://www.mindspring.com/~vco/content.html
>
> Happy experimenting!,
> -Dan G.