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Different ranges of signals along the electromagnetic (EM) spectrum are classed by the size of their wavelengths. These include the visible, microwave, and radio bands. Voice frequency refers to both the audio range of vocal transmission most detectable to the human ear and the voice frequency band used by telecommunications networks for the transmission of speech. This band generally ranges from 300 hertz (Hz) upwards to around 3000-4000 Hz.
Telephony first came about to transmit voice, but has grown to accommodate other types of signals like facsimile, telegraph, and digital transmissions. Thanks to the intelligence behind the human ear at understanding and parsing speech, vocal communication can occur over a wider dynamic range than digital data. Transferring data over human speech transmission lines requires tweaking of transmission parameters. This can include the use of modulator-demodulator (modem) technology, which essentially translates data into analog tones. Fiber networks, on the other hand, translate vocal and data communications into rapid pulses of light.
Communication bands are broken up into three grades: narrowband, voice band, and wideband. Narrowband carries facsimile and teletype signals from 0 to 300 Hz. Voice band, or the voice frequency band, operates within 300 to 4000 Hz to accommodate a wider range of data over dial-up and leased lines services.
Wideband accommodates transmissions over 4000 Hz. These may bundle voice channels of analog transmission. Digital transmission of both voice and data rounds out these point-to-point transmission techniques.
Human hearing occurs at a range between 20 Hz to 20 kilohertz (kHz); it is strongest between 300 Hz and 5 kHz. Adult males may speak from 85 to 180 Hz, while adult females communicate from 165 to 255 Hz. Bandwidth in telephony often occurs around 4 kHz, however, including the guard bands. This may accommodate individual voice frequency signals that are bundled together into wideband transmissions.
The ultralow frequency band between 300 and 3000 Hz comprises the acoustic energy at baseband, or zero to maximum bandwidth for voice transmissions. This band is called the voice frequency (VF) or voice band. For digital communications, the number of times per second voice frequency transmission can be sampled, or its sampling rate, is typically 8 kHz.
This is known as pulse code modulation (PCM), the digital representation of analog vocal signals. In other words, these bandwidth allocations allow human voices to share the same transmission channels, with minimal interference, as other types of data. Messages can be sent intact and amplified back within the auditory range of the human ear.