PoducateMe: Practical Solutions for Podcasting in Education
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the original recording, but the file size will increase. A codec that removes data from the
source file during compression is said to be “Lossy.” A codec that faithfully reproduces
the original audio without discarding information is said to be “Lossless.”
So, what kind of information is removed during compression? Data that is determined by
the compression scheme least likely to be heard by the listener, such as sound that falls
outside the audible spectrum. The compressed audio’s sound quality is not solely a
product of what is removed from the spectrum, but also of the quality of the information
that is preserved. Some codecs perform better than others, and each has its devotees,
based on factors such as perceived sound quality, speed of compression and platform
and software compatibility. The formats available for recording in AHP include:
AIFF (Audio Interchange File Format)
Partly developed by Apple, AIFF is a very popular lossless format for pro recording
on Macs. It supports a variety of bit resolutions, sample rates, and channels of audio.
Additionally, most audio editing programs, including Audacity, are capable of
importing AIFF files. AIFF is virtually identical to WAV (Waveform Audio), which is the
default format for digital audio on Windows PCs.
ALAC (Apple Lossless Audio Codec)
As the name implies, this is an Apple-developed lossless format that that can
compresses an audio CD to about half its original size without loss of quality.
Unfortunately, audio editors such as Audacity do not support ALAC.
MP3
This is the most popular lossy codec for storing and transferring music, and is the
standard format for podcasts. MP3 is able to deliver near-CD sound quality in a file
that's only about a tenth or twelfth the size of an uncompressed recording. It might be
tempting to simply record into this format and save the step of having to compress
your file for the Web, as you would have to do if you recorded using say, AIFF. This
is not recommended, however, as recording into MP3 will put more strain on your
system as it labors to compress the audio as it is being recorded. Also, later on we’ll
be adding uncompressed music to our recording, which will require us to compress
the file anyway. Because compression is cumulative, compressing audio that has
already been compressed has the potential to dull your sound and should be
avoided. We record and edit an uncompressed AIFF file and wait until it’s ready to
upload to our server before applying MP3 compression.
AAC (Advanced Audio Coding) and MPEG-4
AAC forms the nucleus of MPEG-4, which is actually a wrapper for the AAC file
format. MPEG-4 boasts superior sound and smaller file sizes than MP3. Though not
officially standardized, the following file extensions are commonly used for MPEG-4
files:
Files ending in .m4a are audio content only. This is also the extension used
for enhanced podcasts.
