Listening and Recording Film 116
Instructor: Steve Wetzel

Equalizing: voice

Generally speaking, the key to equalization is subtractive not additive.  When
you lower or raise a frequency you're lowering or raising the gain.  Raising
the gain of frequencies willy-nilly tends to bring too much energy to the mix and
tends to over saturate sounds, causing them to needlessly compete with one
another in the mix.  Carefully attenuating frequencies, when done well, can bring
distinction to various sounds in a mix.  So... when boosting or adding to the gain
of a frequency or a band (q) of frequencies (200 Hz - 220 Hz), do so cautiously
and modestly.

The notes below were compiled from a site authored by Robert Dennis.  I simply
extracted the bits relevant to voice.

40 - 80 Hz ("low bass"), centered on 50 Hz
Some sound exists below 40 Hz: thunder, maybe the rumblings of a large vehicle,
stuff like that.  Listen closely for these booming, rumbling tones and take them out
if they do nothing but muddy up the overall sound.  A high pass filter can be applied
to quickly attenuate low frequencies (you simply set the effect > high pass filter with
a cutoff frequency of, say, 70 Hz; the frequencies below 70 Hz are then attenuated while
all frequencies above 70 Hz are left alone).

40 - 80 Hz is generally considered the power set of frequencies.  At low volume the sounds
in this freq (from now on I'll refer to frequency as "freq") range are hard to hear, and may not
be heard at all on lesser or smaller stereo systems.  If there's too much going on in this freq range
the recording will tend to sound muddy, when attenuated a bit the sounds in this freq range can
lend a general sense of power to the mix -- a kind of "bigness" and presence to the mix.


80 - 250 Hz ("bass"), centered on 100 and 200 Hz
Again, too much here can cause the recording/mix to sound muddy and/or "boomy".

200 Hz: fullness of vocal, can be reduced to increase distinction; if vocal feels slight
or meek or thin, a small boost (start with 2 or 3 db) might be necessary.  Too much here
can make the voice sound muddy, bass-y, indistinct.


250 - 500 Hz ("Lower mid"),
250 - 350 Hz can be used to increase distinction and fullness on vocal (esp. "female" vocal).


500 Hz - 2 Khz (2000 Hz), ("Mid")
Reducing at 800 Hz can make voice sound less nasally -- can give it more presence or body.


2Khz - 4 Khz ("Upper mid")
Small boost in here can increase projection in the vocal, too much can make syllables hard to
distinguish and can cause "listening fatigue".


4 Khz - 6 Khz ("Presence"), center on 5 Khz
Small boosts can make vocal feel closer and more present, too much will feel harsh and irritating.


6 - 20 Khz ("Treble")
The vocal "S" sound is typically at 7 Khz.  This frequency is typically lowered, but reducing too
much here can quickly cause the vocal to lose presence.  At 15 Khz and above is the "breath" of the
vocal.  

For more on equalization in Audacity, click here.

For a quick description of EQ via WikiMedia

Applied EQ (music, but can make the leap to voice).