Apple Logic (1.1) - Manual (Page 92)

92 Chapter A Audio and MIDI Basics
The sampling resolution—expressed as bit values—determines the precision of the
measuring scale used to store (the numbers of ) each sample. Remember that
computers store audio files as digital information—a series of ones and zeroes. There
are three audio file resolutions commonly in use: 8, 16, and 24 bits. 24 bit systems are
more expensive and are used extensively in DVD audio and film production.
To give you an idea of the relevance of the sampling resolution, imagine two people
are building a house. One is using a tape measure marked to the nearest foot. The
other has a tape measure marked to the nearest inch. Although the house built with
the tape measure accurate to the nearest foot may not fall down, the one using the
finer scale will build a more accurate house.
About File Formats
Continuing on from the 24 bit and 16 bit resolution discussed above, Logic can record
and play back 16 and 24 bit audio files. You can even use both 16 and 24 bit files in the
same song. The advantage of the higher resolution 24 bit files in Logic is most apparent
when mixing.
Every mixing operation in Logic—a volume change, panning, effects processing, and so
on involves some sort of mathematical calculation. In digital systems, where everything
is represented by ones and zeroes, there are (often) occasions where the calculations
don’t result in a nice, round number. To handle this, Logic will “round off” the value
resulting from the calculation to the nearest suitable value. This is known as a roundoff
correction in digital audio terminology.
If you begin with a 24 bit file, the sample is represented by around 16 million little slices,
whereas the 16 bit file of the same audio is represented by 64 thousand slices—note
that slices is not a technical term, in any way!
As you can see, the higher resolution 24 bit file has far more slices that could be used as
possible values during a roundoff correction. The end result of all of this?
24 bit files retain more of the original character of the sound after processing/mixing,
making your mixes more precise, and largely avoiding coloration of the sound.
About MIDI and Audio File Sizes
Digital audio files consume a great deal of hard disk space. “CD quality” audio with 16-
bit dynamic resolution and 44.1 kHz frequency resolution requires 5 megabytes (MB) of
hard disk space for 1 minute of monophonic audio. For a stereo recording, this
requirement is doubled, with a one minute audio file using 10 MB of storage space.
MIDI file data, on the other hand, is tiny. An average MIDI song file, three minutes in
length and containing a dozen or more tracks will be about 20 kB in size.