Acoustics for Communications

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Digital Telephones – SIP – Proprietary - Wireless

*  Digital Telephone and Wireless testing using industry standards and specialized tests

*  Over 15 years experience in digital telephony audio

*  Telephone Testing using latest electroacoustic test methods – Analog or Digital.

*  Hearing Aid Compatibility - HAC Testing.

*  Acoustic Shock Testing.



Handset Testing on Bruel and Kjaer 4228 HATS with Handset Positioner

Handset on B&K HATS

Handset and Telephone Evaluation

We have the specialized acoustic measurement equipment needed to test telephones.

*    Frequency Response

*    Noise and Distortion

*    Hearing-Aid-Compatibility – HAC

*    Send, Receive, Sidetone Loudness Ratings
     (RLR, SLR, STMR)

*    Weighted Terminal Coupling Loss, TCLw (Echo)

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Bruel and Kjaer Handset Alignment Jig

Handset Positioning Jig


4602 Telephone Test Head with B&K 4227 Mouth and IEC-318 Ear

Traditional Test Head

4227 Mouth - IEC-318 Ear


Graph: TIA-810 Handset Send Frequency Response (Transmit Response)

TIA-810 Send Response

About Digital Telephones 

Digital terminals require specialized test techniques and test interface circuits. Echo, delay, and vocoder artifacts become major factors impinging on voice quality.


The loss plan (loudness ratings) of a telephone must be verified to insure it is compatible with the network loss plan and to insure maximum customer acceptance.


Delivering voice packets at a fast enough data rate without excessive loss, delay, or jitter is such a challenge with VoIP systems that sometimes the fundamental acoustics of the terminal are overlooked. Poor audio and acoustics of a terminal can exacerbate link problems.


Algorithms such as PESQ and PSQM are sometimes employed to estimate overall voice quality (MOS score) but are they not a substitute for quantitative measurement of such metrics as frequency response, distortion, noise, echo loss, gain tracking or for live subjective testing.


AFC owner, Ron Magnuson, was chair of the TIA working group that wrote the digital terminal audio standards for North America - ANSI/TIA-810A and TIA-920 - and has worked on numerous digital voice terminal designs.   He has made technical contributions to TIA-810B.                                             

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Graph: Handset Terminal Coupling Loss TCLw

Terminal Coupling Loss

Wireless handsets – Wireless telephones

From an audio perspective, a wireless device can usually be treated as a digital terminal.  Additional attention should be paid to latency and echo.


Precautions should be taken to prevent the RF section, or power switching currents, from inducing noise into the audio path or causing interference with hearing aids. (see “HAC”, below)

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Hearing Aid Compatibility Graph

FCC Part 68 Hearing Aid Compatibility

Hearing Aid Compatibility – HAC Testing

Handsets sold in the United States are required by the FCC to be compatible with hearing aids. Legally landline telephones must meet two fundamental requirements:

*    Minimum volume control range and loudness.

*    Strength and response of the audio magnetic field.


Recently a new standard, ANSI/TIA-0883 “Handset Magnetic Measurement Procedures and Performance Requirements” has added additional recommendations for magnetic noise and distortion that can be a problem with digital cordless handsets.


I have a great deal of experience in this field including test, research, and technical input to the standards and regulations.                                  

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Acoustic Shock Testing

Acoustic shock is a loud noise from a handset, or headset, that could potentially damage a user’s hearing.


Safety standards, such as those from Underwriters Laboratories, set the maximum acoustic level allowed. A standardized ear simulator is used for this SPL measurement.                                             

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© Ron Magnuson,
Acoustics for Communications

Austin, Texas