SB AWE32 Developer's Information Pack
PART IV MIDI NRPN Implementation
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Copyright
Creative Technology Ltd., 1994-1996
Version 3.00
EMU8000 Sound Elements
The blocks within an EMU8000 sound element can be programmed to produce a variety of sound effects.
Oscillator
An oscillator is the source of an audio signal.
Low Pass Filter
The low pass filter is responsible for modifying the timbres of an instrument. The low pass filter’s filter
cutoff values can be varied from 100 Hz to 8000 Hz. By changing the values of the filter cutoff, a myriad
of analogue sounding filter sweeps can be achieved. An example of a GM instrument that makes use of
filter sweep is instrument number 87, Lead 7 (fifths).
Amplifier
The amplifier determines the loudness of an audio signal.
LFO1
An LFO, or Low Frequency Oscillator, is normally used to periodically modulate, i.e., dynamically
change a sound parameter, whether it be volume (amplitude modulation), pitch (frequency modulation)
or filter cutoff (filter modulation). It operates at sub-audio frequency from 0.042 Hz to 10.71 Hz. The
LFO1 in the EMU8000 modulates the pitch, volume and filter cutoff simultaneously.
LFO2
The LFO2 is similar to the LFO1, except that it modulates only the pitch of the audio signal only.
Filter Resonance
A filter alone would be like an equaliser, making a bright audio signal duller, but the addition of
resonance greatly increases the creative potential of a filter. Increasing the resonance of a filter makes it
emphasis signal at the cutoff frequency, giving the audio signal a subtle “wah-wah”, i.e., imagine a siren
sound going from bright to dull and bright again periodically.
LFO1 to Volume (Tremolo)
As indicated in figure 1, LFO1’s output is routed to the amplifier, with the depth of oscillation
determined by LFO1 to Volume. LFO1 to Volume produces tremolo, which is a periodic fluctuation of
volume. Lets say you are listening to a piece of music on your home stereo system. When you rapidly
increase and decrease the playback volume, you are creating tremolo effect, and the speed in which you
increases and decreases the volume is the tremolo rate (which corresponds to the speed at which the
LFO is oscillating at) . An example of a GM instrument that makes use of LFO1 to Volume is instrument
number 45, Tremolo Strings.
LFO1 to Filter Cutoff (Wah-Wah)
As indicated in figure 1, LFO1’s output is routed to the filter, with the depth of oscillation determined by
LFO1 to Filter. LFO1 to Filter produces a periodic fluctuation in the filter cutoff frequency, producing an
effect very similar to that of a wah-wah guitar (see resonance for a description of “wah-wah”). An