E-Mu Vintage Keys Operation Manual page 43

PROGRAMMING BASICS
••• When the filter Fc is 000
all sound will be cut off. The
initial filter Fc and all Fc
modulators ADD algebra-
ically to determine the actual
Fc. If you are not getting
sound, adjust the initial Fc or
reduce the amount of
modulation. Careful adjust-
ment of all the filter param-
eters is the secret to getting
great sounds.
Most of the instruments in Vintage Keys are complex waves contain-
ing many sine waves of various amplitudes and frequencies. A filter is
a device which allows us to remove certain components of a sound
depending on its frequency. For example, a Low Pass Filter, like the
one in Vintage Keys, lets the low frequencies pass and removes only
the high frequencies.
100
The point at which the frequencies begin to be cut is called the Cutoff
Frequency (or Fc for short). A filter that let only the high frequencies
pass would be called a High Pass filter. Using a filter, we now have a
way to control the harmonic content of a sampled sound. As it turns
out, a low pass filter can simulate the response of many natural
sounds.
For example, when a piano string is struck by its hammer, there are
initially a lot of high frequencies present. If the same note is played
softer, there will be fewer of the high frequencies generated by the
string. We can simulate this effect by routing the velocity of the
keyboard to control the amount of high frequencies that the low pass
filter lets through. The result is expressive, natural control over the
sound.
The auxiliary envelope generator is commonly used to control the
cutoff frequency of the low pass filter. This allows the frequency
content to be varied dynamically over the course of the note. Dy-
namic filtering coupled with all the different instruments available,
makes for almost endless possibilities in the final sound. Any modula-
tion source can be used to modulate the filter.
34 Vintage Keys Operation Manual
80
Output of Filter
60
40
20
40 80 160
Frequency
Cutoff Frequency
...
360 720 1440 2880