[sdiy] They aren't sawtooths, they're ramps

[David G. Dixon]

I put a "sine-or-sigmoid" switch on every VCO I build now, along with a
"centre-or-edge" pulse switch (indeed, it's more or less the same switch).

The sigmoid is an interesting example, because it is a specific, very
precisely defined thing: basically, it is what you get when you put a
sawtooth wave through a sine shaper.  If one were to put a perfect triangle
wave through a perfect sine shaper, one would get a perfect sine wave.
Likewise, one would get a perfect sigmoid wave by putting a perfect sawtooth
through that same sine shaper.  It's just a question of definitions, insofar
as some names should be reserved for specific things.

It is, however, completely up to us in the end.



> "YOU MEAN THE SIGMOID???? :PPP"
> 
> Colloquially know as "Stephensine" ;)
> 
> 
> _Kyle (asked the list a while back what a saw/ramp through a sine shaper
> would sound like) Stephens
> 
> 
> PS: Aaron Lanterman halfway suggested this - I tried running a guitar (aka
> roughly sine) through the Thomas Henry sine shaper, though my gain stage
> was pretty noisy as what I happened to have breadboarded up at the time
> was another effect in progress - got some interesting noises and a
> compression effect at some settings... More tweaking that latter.
> 
> --- On Wed, 11/4/09, cheater cheater <cheater00 at gmail.com> wrote:
> 
> > From: cheater cheater <cheater00 at gmail.com>
> > Subject: Re: [sdiy] They aren't sawtooths, they're ramps
> > To: "David G. Dixon" <dixon at interchange.ubc.ca>
> > Cc: synth-diy at dropmix.xs4all.nl
> > Date: Wednesday, November 4, 2009, 1:30 PM
> > > Waveforms derived from
> > relaxation oscillators definitely do not fit the
> > > bill, and therefore should not be called "sawtooth",
> > any more than some
> > > random "rounded" waveform should be called "sine".
> > >
> >
> > YOU MEAN THE SIGMOID???? :PPP
> >
> > On Wed, Nov 4, 2009 at 20:30, David G. Dixon <dixon at interchange.ubc.ca>
> > wrote:
> > >> snip >
> > >> > "Ramp" refers to the ramping part of the
> > sawtooth wave, but could also
> > >> > refer to waveforms where the ramp is an
> > important part of a waveform
> > >> > that's not really a sawtooth wave.  For
> > example; a wave that starts
> > >> > low, ramps up, holds there for a bit, and
> > then resets.
> > >> >
> > >> > Relaxation oscillators are what they are,
> > they don't define the
> > >> > sawtooth wave.
> > >
> > > I tend to call it a sawtooth when it ramps downward,
> > and a ramp when it
> > > ramps upward.  However, it seems to me that we should
> > reserve the term
> > > "sawtooth" for either upward or downward ramps which
> > are linear; i.e., those
> > > which are generated by a carefully designed VCO
> > feeding a fixed current to
> > > an integrator with one end of the cap pinned to
> > virtual ground, and which
> > > can be counted upon to contain both even and odd
> > harmonics with amplitudes
> > > inverse to their harmonic number.  At least, in synth
> > circles, I think we
> > > should make this distinction.
> > >
> > > Waveforms derived from relaxation oscillators
> > definitely do not fit the
> > > bill, and therefore should not be called "sawtooth",
> > any more than some
> > > random "rounded" waveform should be called "sine".
> > >
> > >
> >
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> >
> 
> 
> 
> 
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