Recording A Sound - CAKEWALK PRO AUDIO User Manual

envelope, and each has its own complex combination of frequency
components, which can change across the duration of the sound.
The center line of a waveform is the zero line; it corresponds to the rest
position (displacement of 0) of the original vibrating object. (A waveform
for perfect silence would be a horizontal line at zero.) Back and forth
motions of the vibrating object translate to upward (positive) and
downward (negative) excursions of waveform amplitude. For example, a
close-up of a portion of the guitar waveform might look like this:
The waveform crosses the zero line twice during each complete vibration.
These zero-crossings are important in digital audio processing; they
are good places to cut waveforms apart and splice them together. If
waveforms are cut or spliced at other locations, clicks and pops can occur.
The maximum amplitude of the waveform in each vibration is also
important: it determines the strength of the vibration, and thus the
loudness of the sound.

Recording a Sound

To record digital audio, your computer monitors the electrical signal
generated by a microphone (or some other electroacoustical device).
Because the signal is caused by a sound, the signal strength varies in
direct proportion to the soundÕs waveform. The computer measures and
saves the strength of the electrical signal from the microphone, thus
recording the waveform.
There are two important aspects of this measuring process. First is the
sampling rate, the rate at which the computer saves measurements of
the signal strength. It is a known fact of physics that you must measure,
or sample, the signal at a rate at least twice that of the highest
frequency you wish to capture. For example, suppose you want to record
a moderately high note on a violinÑsay the A whose fundamental
frequency is 440 Hz and all overtones up to Þve times the fundamental.
The highest frequency you want to capture is 2,200 Hz, so you need to
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