Suggestions for the person speaking

It is seldom practical to try altering the behavior of the person speaking, and generally impossible to affect a change in the actual sound produced. However, there are a few suggestions that could be shared with any speaker who is interested.

1. “Speak up!” If the speaker is aware that additional effort is needed, it can actually cause involuntary changes in speech for improved clarity (Lombard effect), in addition to a simple signal-to-noise ratio increase at the microphone.

2. It can be counter-productive for the lips to be closer to the microphone than about 3 inches. This is caused by the proximity effect, which increases low frequency gain and thus reduces the signal-to-noise ratio. The speaker should move closer to the microphone only when the system has feedback or gain problems—it should not be necessary with correct system design. (Unfortunately, however, feedback and gain problems are very common.)

Frequency ranges

Having covered some suggestions for the speaker, we now are concerned with the technical characteristics of voice so we can understand what our “signal” actually is.

• Typical adult male speech fundamental frequency: 85 Hz to 180 Hz.

• Typical adult female speech fundamental frequency: 165 Hz to 255 Hz.

• Child’s speech fundamental frequency: 250 Hz to 300 Hz or higher.

• Maximum vocal range: 65 Hz (male) to 1.28 kHz (female).

• Sibilance, or essing, is the high frequency “hissing” sound associated with the letter s and many other consonants. Sibilants range from 2 kHz to 10 kHz.

• Speech critical range: approximately 170 Hz to 8.3 kHz.

• Range for high-fidelity speech reproduction: 80 Hz to 12 kHz.

• As comparison, a standard piano keyboard covers tones from 27.5 Hz to 4.186 kHz.

Sources:

• Wikipedia: Voice frequency

• Axiom Audio: Frequency Ranges of Male, Female, and Children’s Voices

Speech critical bands

The following is a selection of narrow frequency bands which may be treated as the elementary signals in speech. This is from Gdansk University of Technology Multitask Noisy Speech Enhancement System.

Consequently, on a 1/3 octave equalizer, the following bands are especially important:

• 160 Hz

• 200 Hz

• 250 Hz

• 315 Hz

• 500 Hz

• 800 Hz

• 1 kHz

• 1.6 kHz

• 2 kHz

• 3.15 kHz

• 5 kHz

• 8 kHz

Interestingly, all other bands can be reduced quite a lot without noticably impacting audio quality. However, I do not recommend doing so for normal operation, as everything from 80 Hz to 10 kHz is important for high-fidelity speech reproduction.