PoducateMe: Practical Solutions for Podcasting in Education
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Sample Rate and Bit Depth
“Sample rate” and “bit depth” directly affect how closely your recording will match the
signal being recorded. Together, these two properties determine the “resolution,” or
amount of detail captured in the recording.
The sample rate refers to how many times per second the analog source material
(your voice, for example) is analyzed and converted to a digital format. CD-quality
audio is sampled at 44.1kHz (44,100 times per second), while standard DVD-Audio is
sampled at 96kHz (96,000 times per second).
The Nyquist Theory states that in order to record the highest frequency to be
reproduced, you must sample at a rate of at least two times that frequency. Thus, in
order to reproduce the full frequency range of human hearing (20Hz to 20kHz) a
sampling rate of at least 40kHz (two times 20kHz) is needed. While a debate rages
as to whether or not it’s worth recording at sample rates that reach beyond the
audible spectrum, many audio engineers insist that doing so will yield superior fidelity
(and larger file sizes!).
Sample resolution is determined by bit depth, which refers to how many bits (the
smallest unit of computer data) are used to describe each of the samples taken.
Generally, the more bits that are used, the more accurate (less noisy) your
recordings. All CD music is distributed at a resolution of 16-bit/44.1kHz, typically
compressed from an original 24-bit studio recording.
If you see an interface spec of 24-Bit/48kHz, it means that the unit’s audio converters
are capable of processing signals at a level beyond that typically used to record CD-
quality sound (24-Bit/44.1kHz, before it is compressed to 16-bit/44.1kHz). Today, a
top-of-the-line interface can yield resolutions up to 24-Bit/192kHz.
If you wish to record at high resolutions, you must make sure that you have a
generous amount of disk space and computing power, and that your recording and
editing software is capable of handling the data. Apple’s GarageBand audio
recording/editing software, for example, can only export a 16-Bit/44.1kHz file. Thus,
by recording in GarageBand, the benefits of purchasing an interface capable of
processing audio at 24-Bit/192kHz would be lost.
16-Bit/44.1kHz resolution has become a general standard for podcasters, and most
should find this quality of audio more than acceptable. It’s important to note that
because your recordings will ultimately be compressed for distribution over the
Internet, the increased fidelity your audio receives when recorded at higher
resolutions will be trimmed during the compression process.
Many interfaces will come bundled with a stripped-down version of some brand of
professional recording software capable of recording at resolutions supported by the
unit. Recording software will be discussed a bit later, but for now, you need only
