How do I describe this waveform?

[steve]

Sawtooth: http://en.wikipedia.org/wiki/Sawtooth_wave

I'm working on an "unofficial TS404 BETA user guide", to try to get more people making their own samples. I want to include some verbiage as well as pictures to try to make the whole process of synthesization less complex. My thought is, sure, just moving stuff around is okay and you CAN eventually get some sounds, but maybe knowing what is happening would be a better start. Anyways, I guess I'll go with "half wave".

It's so much easier to give a relevant response when the question has context.
I think "half wave" is a pretty good description.
or perhaps a "negative going sawtooth".

Just as a matter of interest, you can generate a pretty good approximation to that "half wave" with the following Nyquist code:

Code: Select all

;type generate

(setq !TEMPO 180) ; beats per min
(setq piano-key A1) ; note in standard MIDI notation

(setq i (/ 60.0 !TEMPO)) ; note length

(defun env (s-in) ; apply envelope
  (setq t (get-duration (* i  0.7)))
  (mult s-in (pwl 0 1 t 0.5 t 0 1)))

(defun note (pitch dur) ; create waveform
  (env (sum -0.25 (mult 0.25 (osc pitch dur *saw-table*)))))

(note piano-key i) ; generate the note

[Trebor]

Well, it's DEFINITELY a triangle wave not a sawtooth.

I refer the honourable gentleman to the answer I gave a few post ago ..

sawgiff.gif (41.58 KiB) Viewed 728 times

http://en.wikipedia.org/wiki/File:Waveforms.svg

This is a sawtooth.

http://forum.audacityteam.org/viewtopic ... 091#p97091

exponential.gif (59.3 KiB) Viewed 725 times

That is part sawtooth (or possibly square wave) and part exponential, (like charging a capacitor).

[kozikowski]

<<<like charging a capacitor>>>

Except for the downward going bits.

Koz

[DickN]

The first is a sawtooth with decreasing amplitude and no DC component.
The second is also a sawtooth with decreasing amplitude, but it has a negative DC component proportional to the amplitude.

Not useful in audio, but analogous nonetheless, is what's called a "DC restorer" circuit which is used in TV sets that have AC coupled video amplifiers. The same circuit, given the first waveform (at the frequency of the 2nd one) would produce the second waveform.

The DC restorer is just a diode across the load side of a coupling capacitor, which clamps the positive extreme of the waveform to a fixed voltage (in TV, it's the top of the horizontal sync pulse). In the valve days, the control grid of the sync separator typically served as the diode. The top of the sync pulse serves as a reference level just beyond black. Without DC restoration, the black level would vary from beyond black to gray as the contrast of the scene varied. In color TV, the saturation levels would be totally hosed.

[DickN]

The waveform exponential.gif looks like a sawtooth which has been AC coupled with a time constant which is too short. The short time constant high-pass filters the waveform. Near the top of the original sawtooth, the output of this (single pole) high-pass filter approaches a DC value proportional to the slope of the rising portion of the waveform. The flat bottom suggests that the resulting waveform has been clipped by a later stage, and the fact that the clipping level of the bottom varies with amplitude suggests that the result is AC coupled again in a later stage.