Apple Final Cut Express HD - Manual (Page 590)

590 Part VIII Audio Mixing
Bit Depth
Unlike analog signals, which have an infinite range of volume levels, digital audio
samples use binary numbers (bits) to represent the strength of each audio sample. The
accuracy of each sample is determined by its bit depth. Higher bit depths mean your
audio signal is more accurately represented when it is sampled. Most digital audio
systems use a minimum of 16 bits per sample, which can represent 65,536 possible
levels (24-bit samples can represent over 16 million possible levels).
To better understand bit depth, think of each digital audio sample as a ladder with
equally spaced rungs that climb from silence to full volume. Each rung on the ladder is
a possible volume that a sample can represent, while the spaces between rungs are in-
between volumes that a sample cannot represent.
Often, when a sample is made, the audio level of the analog signal falls in the spaces
between rungs. In this case, the sample must be rounded to the nearest rung. The bit
depth of a digital audio sample determines how closely the rungs are spaced. The more
rungs available (or, the less space between rungs), the more precisely the original
signal can be represented.
The diagram on the far right has the highest bit depth, and therefore the audio
samples more accurately reflect the shape of the original analog audio signal.
Any audio level that cannot be represented must be rounded to the nearest acceptable
value. For example, a 1-bit system (a ladder with only two rungs) can represent either
silence or full volume, and nothing in between. Any audio sample that falls between
these rungs must be rounded to full volume or silence. Such a system would have
absolutely no subtlety, rounding smooth analog signals to a square-shaped waveform.
Analog waveform Audio sample
Sine Square