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
_____
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From: emlsynth@yahoogroups.com [mailto:emlsynth@yahoogroups.com] On Behalf
Of Matt
Sent: Friday, February 20, 2009 2:14 PM
To: emlsynth@yahoogroups.com
Subject: [emlsynth] EML-101 amplitude modulation
sorry for my ignorance, but what exactly is 'amplitude modulation' on
the EML-101? To my ears it seems to be some sort of distortion/FM, but
I don't understand why it's on the same control as the ring modulator
and how one can morph into the other. The manual, as usual, is totally
useless in this respect.
After what must now be 9 months with the 101 what I like most about it
is the fact that I'm never quite certain what's going to happen when
I turn a control, although I wish I could make sense of the patchbay,
with which I seem unable to achieve anything beyond patching in OSC1's
audio signal. Matt
