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Mysterious Eagle Audio Generator - Any ideas?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion Goto page Previous  1, 2 [all]
Author Mysterious Eagle Audio Generator - Any ideas?
ranix
Synthiq wrote:
calaveras wrote:
Love to see that on a scope.

Not on a scope, but sampled with Audacity. Is this supposed to be a squarewave?



this, in fact, is a square wave. It looks like it's been passed through a DC blocking filter.

Don't fuck with it if it's shocking you, gotta fix it first. Don't mess with equipment like this if it has ground faults. It's seriously dangerous.
alexbarbed
You got mixed up, it wasn't this that was shocking me, it was a Tascam desk, a long time ago.
Synthiq
ranix wrote:
this, in fact, is a square wave. It looks like it's been passed through a DC blocking filter.

Then, technically, it was a square wave before the highpass filter, sort of. Integrating the signal can more or less restore the original waveform but it is less than an ideal square wave. And as a side note, the frequency is 40 Hz and not 120 Hz. Would I spend time fixing it? Probably not.

ranix
alexbarbed wrote:
You got mixed up, it wasn't this that was shocking me, it was a Tascam desk, a long time ago.


aaah, ok. That's good news, this oscillator looks really cool thumbs up
alexbarbed
Synthiq wrote:
Integrating the signal can more or less restore the original waveform

What just happened? What did you do to 'restore the original waveform?'
Synthiq
alexbarbed wrote:
What just happened? What did you do to 'restore the original waveform?'

Maybe not a mathematically stringent explanation, but a highpass filter acts a little like a differentiator outputting a signal proportional to the change in the input signal and in your original example you can see a positive spike and half a period later a negative spike corresponding to the positive and negative edges of a square wave.

The inverse function to an differentiator is an integrator so if you integrate the differentiated signal you get the original signal back again and that's what I did. I put together a simple integrator in the LTSpice circuit simulator and it read your wave file as the input signal and wrote the output to another wave file.

A circuit simulator like LTSpice is a great tool to test design ideas quickly and without a lot of lab equipment, so it's worth learning how to use one if you do any circuit design.
alexbarbed
OK, thanks. I don't do circuit design and barely understand what you said, but I have had a look at LTSpice and it looks very interesting.

You said that the frequency was actually 40Hz, yet when I look at it in a frequency analyser the fundamental is at 120Hz. Would you mind telling me what I have got wrong there?
Synthiq
If you look at the time scale of the plots, it is clear the spacing between two periods is about 25ms which corresponds to 40Hz. I did analyze the distortion of your signal at time 6 seconds and the third (and seventh) harmonic is about the same strength as the fundamental, so that might have caused your frequency analyzer to report 120Hz. I only looked at the harmonics at one time and it may change over time so the third harmonic might very well have been stronger when you measured the frequency. Some counters measures the number of zero crossings (with some hysteresis) so it is possible it found 3 positive zero crossings per real period since there is quite a bit of activity going on all the time, not just where the edges are. With a complex signal like this, it is not unexpected if the wrong frequency is reported.

alexbarbed
You're a good wave doctor. When I have wave trouble in future, I'll know who to call thumbs up
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