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

[Jerry Gray-Eskue]

I have references that date back to the 70s and they consider Saw and Ramp
to be the same thing, a sharp vertical rise (or fall) and a linear slope.

A (pure) sine wave has only the fundamental frequency.
A saw or ramp wave has all the harmonic overtones of the fundamental
frequency decreasing exponentially with the harmonic series.

A triangle wave (1/9,1/25,1/49...) and square wave (1/3,1/5,1/7,1/9...) has
all the odd harmonic overtones of the fundamental frequency.

The ratios of the harmonics and odd even content define the wave shapes.

<<However, original relaxation oscillators generated exponential rises and
falls >> This would be rich in harmonics but I am not sure of the harmonic
content.



-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Electronic
Battle
Sent: Monday, November 02, 2009 11:22 AM
To: synth-diy DIY
Subject: [sdiy] They aren't sawtooths, they're ramps


Hello All

Please can someone talk about the difference between sawtooth and ramp
waveforms and whether they sound different?

Mere nomenclature and semantics possibly, but nevertheless, most VCO cores
these days are (as far as I have seen) integrators which provide a constant
current charge pump into a capacitor and get a linear voltage generated at
the op-amp output. You get a linear rise and fall of the triangle wave which
can be processed into a ramp.

However, original relaxation oscillators generated exponential rises and
falls - these are the true sawtooths.

Have a look here:

http://www.eng.cam.ac.uk/DesignOffice/mdp/electric_web/Exper/05263.png

The module front panel says "saw" but the waveform says "ramp"
http://yusynth.net/Modular/index_en.html

The ASM VCO core says "saw" but it is actually ramp.


So VCOs which say "saw" on the front are actually generating ramps: what is
the sonic difference though? Is the harmonic makeup radically different -
what would the fourier spectrum look like and would it sound that different?


None of this meant to sound like any kind of a criticism by the way, merely
an observation.  IS the sonic difference i.e. an audible A:B comparison able
to identify two distinctly different tones?


EB


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