PoducateMe: Practical Solutions for Podcasting in Education
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Figure 11: Frequency response curve for Shure KSM27 with filters applied
Note how this microphone’s filters allow the user to cut off, or more delicately, roll off,
bass frequencies to lessen the proximity effect and low frequency rumble. Lavalier
mics exhibit extreme low frequency rolloff to help attenuate the sound of the mic
brushing up against the user’s clothing.
Sensitivity
Sensitivity is the minimum amount of input signal (such as your voice) required to
drive a microphone to its rated output level. The overall sensitivity will also determine
how much you have to increase the signal level (gain) on the mixer or mic preamp to
bring the microphone output up to its required recording level. The more gain you
add to a signal, the more background hiss is generated. Thus, a high sensitivity rating
is generally more desirable than a low one.
Look for sensitivity of 10 mv/PA (10 millivolts per Pascal, a measure of how many
millivolts a mic will output per a given sound pressure level) or higher.
Equivalent Noise Level (Self-Noise, Noise Floor)
Self-noise is the electronic noise (often a hum) made by the circuitry of condenser
microphones (since dynamic mics have no active electronics, they have very low self-
noise). Electronic noise is especially an issue for podcasters, as most are not likely to
have loud drums or guitars to drown out the unwanted signals.
Specs in this area usually show the figure in dB(A), or "A weighted." A weighted
means that a low frequency roll-off curve has been applied, which gives the mic a
more favorable (lower) rating. Try to purchase a mic with a measurement no higher
than 15dB(A).
Some manufacturers will use the CCIR 468-1 scale to present a self-noise score.
Since this scale uses an alternative weighting technique to dB(A), consider 30dB
good, 22dB very good, and 14dB or lower excellent.
