Providing Network Professionals The Edge

Voice Fundamentals – Human Speech Frequency

What do you think of this post?
  • Useful 
  • Boring 
  • Sucks 
  • Awesome 
  • Interesting 

Human SpeechThe mechanics behind human voice production are unique and in many ways quantifiable.  Understanding human speech and its perceived properties are an important factor when it comes to the development and engineering of communications equipment.  The following are some salient points associated with the production of human speech.

Human speech results from air being forced from the lungs, through the vocal chords and along the vocal tract which stretches from an opening in the vocal chords to the mouth and nose.  Speech is made up from a number of different types of sound which include voiced sound, unvoiced and plosive.  The voiced sounds result from the vocal chords vibrating and thus interrupting the flow of air from the lungs and producing a frequency range of sounds of roughly 50 to 500Hz.  Unvoiced sounds result when air passes some impediment in the mouth or constraint in the vocal tract.  Finally, plosive sounds are sudden bursts of air being let out for example when the vocal tract is closed and suddenly released or the mouth is suddenly opened.  All of these sounds are influenced by the person’s sinuses and nasal cavities and all make up what we understand as normal human speech.

The resultant sound and the mix of frequencies which are produced by these different sound sources are what determine the unique sound of each person’s voice.  These range of frequencies can vary dramatically from one person to another.  However there is a generality in frequency of human speech which can be (and has been) used for the basis of designing telephony equipment for decades.

3.4kHz Frequency

Typically, frequencies in the range of 50Hz and upwards are generated in human speech.  The majority of the energy is concentrated between 300Hz and 3kHz.  The human ear, on the other hand, can detect sounds over a range of frequencies from around 20Hz to 20kHz with most sensitivity in the region between about 300Hz and 10kHz.  With the account of these factors along with functional testing the frequency range of 300Hz to 3.4kHz has been found to be the most important for speech intelligibility and speech recognition.

Reducing this (300Hz to 3.4Khz) bandwidth can significantly reduce the speech intelligibility however increasing it has been found not to significantly improve recognition or the intelligibility.  Please note that increased bandwidth will improve overall sound quality however the incremental gains in sound quality have to be weighed against increased frequency usage.

The frequency band of 300Hz to 3.4Khz is therefore used in our everyday telephone system.  In reality this range of bandwidth provides exceptionally understandable speech and has been the basis of our society’s telephony equipment for many decades.

In a future article I will cover the topic of digitizing this (analog) voice into binary 1s and 0s, along with modern day packetization of these 1s and 0s also know as VoIP.


Voice Fundamentals, Nortel Networks, 2001

Cisco IP Phone TFTP File Look Up Order

Cisco TFTP File Download

Once a Cisco IP Phone has received its IP address, VLAN information and TFTP IP address information (see IP Phone Boot Process article) its next mission is to contact the TFTP server to attain its configuration files.  There is a specific order in … [Continue reading]

Original Selsius IP Phone

Selsius Cisco IP Phone

Selsius Systems was a telecommunications company in Dallas, Texas which developed and marketed some of the first IP telephony products in the industry. It was acquired by Cisco Systems in 1998 and is the basis for the Cisco Unified Communications … [Continue reading]

How to Configure a VWIC2-2MFT-T1/E1 Card on a 2800 Series Router


Enter the following command to determine which WIC slot your VWIC2-2MFT-T1/E1 is installed in: show diag The output of this command will appear similar to below: WIC Slot 2: VWIC2-2MFT-T1/E1 - 2-Port RJ-48 Multiflex Trunk - T1/E1Hardware … [Continue reading]

Cisco 2800 Series ISRs – 2801, 2811, 2821, 2851 Features


The Cisco 2800 series of Integrated Services router platforms are one of my favorites due to their flexibility in accommodating a host of new and legacy modules.  This makes them very highly configurable to suit the needs of any large or small voice … [Continue reading]

Phone Signalling: On Hook, Dial Tone, Pulse, DTMF


Supervisory signalling, Information signalling or Address signalling, these are the groupings to define the various states, tones and methods to setup a phone call between parties.  The following is a quick reference for your viewing … [Continue reading]

The Four Enemies of Voice and Video Traffic

VoIP bandwidth delay jitter

It is the never ending battle of real time voice and video traffic against the following evil foursome.  Here is a quick reference of who/what they are and the metrics required to keep them in check: Delay: According to Cisco and IEEE … [Continue reading]

Cisco Gatekeeper Bandwidth Allocation

A Cisco Gatekeeper has a pre-defined bandwidth number which it allocates per call (based on the CODEC being used). These values are not typically associated with these standard CODECs so I thought I would include these here for reference. The … [Continue reading]

SIP Response Codes

SIP Response codes are a means of communication for the Session Initiation Protocol.  They are pre-defined responses to SIP Requests which have been organized in relevant groups. 1xx—Informational Responses 100 TryingExtended search being performed … [Continue reading]

Cisco IP Phone SCCP (Skinny) Call States

Cisco IP Phone SCCP (Skinny) Call States This is a list of SCCP call states sent by CUCM to SCCP endpoints: 1—Off Hook 2—On Hook 3—Ring Out 4—Ring In 5—Connected 6—Busy 7—Line In Use 8—Hold 9—Call Waiting 10—Call … [Continue reading]

%d bloggers like this: