eml synthesizers

Hi Matt,

Amplitude modulation is exactly that. A control signal changes the amplitude, or the volume of the signal. If the control signal is a low frequency, like from the LFO, it changes the volume up and down at the LFO speed. This is known as tremolo.

When you use an audio signal to modulate the volume, Interesting things happen. In amplitude modulation, you hear the original signal plus the sum and difference of the original and modulating signal. So, if the original signal is 1000 hz and the modulating signal is 100 hz, you would hear three tones. One at the original frequency of 1000 hz, the difference at 900 hz ( 1000-100) and the sum at 1100 hz. (1000 + 100) This is exactly the same process as full blown broadband AM radio (Guess what the AM stands for) only, for audio, it’s a LOT slower. Since the tones aren’t harmonic equivalents, they sound clangy and bell-like.

If you leave the sum and difference frequencies there and remove the original signal, you have what is commonly called ring modulation. In radio terms, it would be called suppressed carrier broadband, or double-sideband AM.

If you could look at a spectrometer connected to the VCA output, you would see the original signal. As you turn the modulation control, you would see the sum and difference frequencies come in and get more prominent. As you turn the control toward ring, the original signal starts dropping out. At the ring position, the original signal is gone and the two sum and difference signals remain.

Remember. FM is the same process only, you’re modulating the frequency, or pitch of the signal, not the volume. At high modulation rates, they can sound similar but are very different processes.

The very fact that you CAN morph from AM into ring modulation on the 101 proves that they were innovative beyond their years. Most other systems can have AM or ring modulation but, nothing in between.

George Mattson