[sdiy] saw/ramp from square?

[Scott Nordlund]

It's sort of like half a standard saw VCO.  An integrator uses a control voltage like an ordinary VCO, but the reset signal comes from a digital clock rather than being triggered by the integrator's output reaching a certain threshold.  The point is that you can get a nice saw waveform without worrying about steppy digital binary weighted octave dividers (like in the Poly 800), precise exponential amplifiers, autotune algorithms, etc.

It's not so simple to just make a box for this because it needs a control voltage to keep the saw wave's amplitude constant as the pitch changes.  If you have this, it's no problem (though it needs to be scaled if the square wave is going through a divider or something).  If you don't, you could use a frequency to voltage converter to generate the CV, but this causes as many problems as it solves (due to latency, there will be a glitch whenever the pitch changes quickly).

A simpler way to get a "sort of" saw would be to highpass filter the square wave and then half-wave rectify the output.  It will have a strange formant (and will similarly impart this formant when used for PWM), but it's still good for some purposes. You could also alter the wave shape by adjusting the highpass filter or DC offset on the rectifier.

----------------------------------------
> From: subjectivity at hotmail.com
> To: synth-diy at dropmix.xs4all.nl
> Date: Wed, 31 Dec 2008 20:13:40 +0000
> Subject: [sdiy] saw/ramp from square?
>
>
> this article (on the DCO's in the JUNO)
>
> http://www.electricdruid.net/images/dcos/larger/JunoDCOwaveshaper.gif
>
> (from
> http://www.electricdruid.net/index.php?page=info.junodcos
>
>
>
> explains a process for getting a ramp from a square. however...i am a bit lost.
>
> is this diagram showing that the square wave plugs straight into the base of the NPN after passing through some caps and resistors (is that an integrator?)
>
> i would LOVE to be able to find a way to get pretty good (dont need to be perfect) ramp waves or (anything other than square) out of my square waves
>
>
> i had heard at some point that ELEKTOR magazine used to run lots of wave shaping articles back in the 70's,
>
> any ideas?
>
> thanks
>
> AND HAPPY NEW YEAR TO ALL YOU SDIYERS!!
>
>
>
>
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