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

[Harry Bissell]

If the relaxation oscillators are driven from a current source, they generate
linear ramps.  If the current source is approximated by a fixed resistor (like in
old neon-tube organ generators) they give an exponential (or quasi-exponential)
response.

They will sound different, slightly imho

Maths experts will now take over with actual spectra... :^)

H^) harry




----- Original Message -----
From: Electronic Battle <electronicbattle at googlemail.com>
To: synth-diy DIY <synth-diy at dropmix.xs4all.nl>
Sent: Mon, 2 Nov 2009 12:22:07 -0500 (EST)
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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-- 
Harry Bissell & Nora Abdullah 4eva