Equalization Key Frequencies
Some History
Dating as far back as the 1930's, the equalizer is the oldest and probably
the most extensively used signal processing device available to the recording
or sound reinforcement engineer. Today there are many types of equalizers available, and these vary greatly in sophistication, from the simple bass
and treble tone control of the fifties to advanced equipment like the modern
multi-band graphic equalizer and the more complex parametric types. Basically,
an equalizer consists of a number of electronic filters which allow frequency
response of a sound system or signal chain to be altered. Over the past
half century, equalizers design has grown increasingly sophisticated. Designs
began with the basic 'shelving filter', but have since evolved to meet
the requirements of today's audio industry.
Understanding EQ
and its Effects on Signals
There are two areas of equalization that I want to cover. Those two
areas are vocals and music. I'd like to discuss the different effects of
frequencies within audio signals. What do certain frequencies do for sound
and how we understand those sounds. Why are some sound harsh? Why do things
sound muddy? Why can't I understand the vocals? I'll try and answer all
of these question and hopefully bring some light to the voodoo world of
EQ.
Vocals
Roughly speaking, the speech spectrum may be divided into three main
frequency bands corresponding to the speech components known as fundamentals,
vowels, and consonants.
Speech fundamentals occur over a fairly limited range between about
125Hz and 250Hz. The fundamental region is important in that it allows
us to tell who is speaking, and its clear transmission is therefore essential
as far as voice quality is concerned.
Vowels essentially contain the maximum energy and power of the voice,
occurring over the range of 350Hz to 2000Hz. Consonants occurring over the
range of 1500Hz to 4000Hz contain little energy but are essential to intelligibility.
For example, the frequency range from 63 to 500Hz carries 60% of the
power of the voice and yet contributes only 5% to the intelligibility.
The 500Hz to 1KHz region produces 35% of the intelligibility, while the
range from 1 to 8KHz produces just 5% of the power but 60% of the intelligibility.
By rolling off the low frequencies and accentuating the range from
1 to 5KHz, the intelligibility and clarity can be improved.
Here are some of the effect EQ can have in regards to intelligibility.
Boosting the low frequencies from 100 to 250Hz makes a vocal boomy or chesty.
A cut in the 150 to 500Hz area will make it boxy, hollow, or tube like.
Dips around 500 to 1Khz produce hardness, while peaks about 1 and 3Khz
produce a hard metallic nasal quality. Dips around 2 to 5KHz reduce intelligibility
and make vocals woolly and lifeless. Peaks in the 4 to 10KHz produce sibilance
and a gritty quality.
Effects of Equalization on Vocals
For the best control over any audio signal, fully parametric EQ's are
the best way to go.
- 80 to 125
- 160 to 250
- 315 to 500
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- Sense of power in some outstanding bass singers.
- Voice fundamentals
- Important to voice quality
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- 630 to 1K
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- Important for a natural sound. Too much boost in the
- 315 to 1K range produces a honky, telephone-like quality.
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- 1.25 to 4K
- 5 to 8K
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- Accentuation of vocals
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Important to vocal intelligibility. Too much boost between 2 and 4KHz
can mask certain vocal sounds such as 'm', 'b', 'v'. Too much boost
between
1 and 4KHz can produce 'listening fatigue'. Vocals can be highlighted
at the 3KHz
area and at the same time dipping the instruments at the same frequency.
Accentuation of vocals:
The range from 1.25 to 8K governs the clarity of vocals. Too much in the
area of 5 to 16K can cause sibilance.
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