Emax II operation manual
193
looping isn’t good, the sound would be less realistic than recording the regular sound
along with its natural decay.
Suppose we sample a sound that has a fairly bright pluck-type attack, then settles down
into sustain. Further assume that the noise is noticeable during the sustained portion of
the sound. Carefully setting the filter envelope can minimize this noise. Since this kind
of problem is most common with bass (there are fewer high frequencies to mask any
noise), we’ll use a bass sound to illustrate this technique.
First, since you’re dealing with a plucked, percussive sound, set the filter envelope for
a short attack. Also, since we have a bright attack, we want to make sure that the envelope
interacts with the filter cutoff in such a way that the filter passes the full bandwidth of
the signal during the initial attack.
In many ways the initial attack, which contains complex harmonic and amplitude
changes, is the most important part to the ear in identifying a sound. It takes only about
50 to 150 milliseconds to recognize the difference between, say, a trumpet and a guitar.
After this period of time, the signal tends to settle down into a more repetitive pattern
that is of less interest to the ear. If some other instrument begins playing during the decay
of the original sound, your ear will tend to focus its attention on the new sound.
We can take advantage of this psycho-acoustic phenomenon to reduce the apparent
amount of noise that occurs after the attack. Consider the diagram below, a spectrum
analysis of the signal being sampled. Here we can see that the initial pluck consists of lots
of high frequency energy—energy that tends to mask any noise. After about 100
milliseconds of this initial burst, the signal loses high frequencies and consists mostly of
lower frequencies. Most of the high frequencies are contributed by the noise. This means
that we can lower the filter cutoff frequency and therefore, cut out the high frequencies,
where the noise is most noticeable,while leaving the low frequencies, where the signal
is, virtually unaffected.
THE ART OF SAMPLING
Maniplulating Samples
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