I just plugged my LP into my PC with some harmonic analysis software.
It seems that I can’t get a pure waveform that has only odd harmonics (Square , Triangle). At the lowest setting of the wave knob (even tried the precision mode, but it’s at 0 anyway) and at the square wave mark on the dial I some level of even harmonics (around -20dB from the odd ones), the patches sound fine, but I wonder is something wrong with my PC/software or is there something wrong with my LP. The only thing I notice soundwise is that the Triangle wave is a little to bright for me comparing to other triangles i’ve heard (it has a certain amount of buzzz in it)
it’s not a mathematically perfect triangle wave. Actually none of the waveforms are mathematically perfect because they are being generated in a complex physical system (it’s analog, baby!). In particular though, the triangle wave is created by a sawtooth-core oscillator which has its waveform reflected to create a triangle from the saw. The point at which the wave is folded/reflected has a tiny artifact which shows up as those extra harmonics. Usually if you roll the filter down a bit you’ll get a pretty close approximation of a smooth triangle, because the artifact is very high in the frequency spectrum.
This is a classic experience. If you check out Wendy Carlos’ Secrets of Synthesis you’ll find she was very surprised to find there was little audible difference between pulse and sawtooth waves that naturally looked totally different on the oscilloscope. She wondered if there was something wrong with the equipment as well.
Certainly what we might think of as `pure’ in terms of visual shape or readout of harmonic content isn’t necessarily what our ears recognise and respond to.
Do this measuring again using different levels of the oscillator going in the filter. You should notice a change in the spectrum. The filter is not a mathematical correct one. If the Moog filter would be “right”, we would not remember the name Moog at all.
There is some distortion going on.