I’m doing simple amplitude modulation using two sine waves. The result should be two sidebands plus the carrier.
However, I’m getting extra sidebands across VCA modules. Only one module I’ve tried seems to work correctly.
Here is a minimal starting point, no AM. Two wave table oscillators are producing sine waves at 60 and 400 Hz. Wavetable VCOs were chose to give perfect sine waves with no additional harmonics. As you can see in the scope, there is only one harmonic for each:
If the fundamental VCA is used for AM, additional sidebands appear at sideband harmonics (multiples of 60). The direct connection to the scope has been left here because the color contrast clearly shows the carrier present in the VCA output:
Extra sidebands appear with VCAMP, though not as many. This could be due to just a difference in gain:
I’ve tried a bunch of modules, and the only one that works as expected is AMP (I’d show, but I’m limited on how many pictures I can post).
I’m wondering if there is some analogue circuit emulation that is creating extra sidebands with most modules?
Also weird: if I ring mod, everything works correctly (two sidebands and no carrier), for example with feidah (it’s bipolar) - can’t show again, embedded picture limit.