AudiologyOnline Phone: 800-753-2160


ReSound Smart Fit - August 2024

Compression v. Expansion

Tammara Stender, AuD

April 23, 2012

Share:

Question

What's the difference between "compression" and "expansion" in hearing aids?

Answer

If you have ever been confused by the definitions of compression and expansion, you're not alone. Part of the reason for this is that from an audiological viewpoint, they each seem to do something opposite of what the name implies. Wide Dynamic Range Compression (WDRC) makes a broader range of sound intensities audible for the user. Although it is compressing the wide range of sound intensities into the limited dynamic range of the hearing aid user, it can also be thought of as expanding the range of sounds that are made audible. Expansion, on the other hand, reduces audibility for very soft sounds. Also commonly known as "microphone noise reduction", expansion is intended to keep the hearing aid from amplifying very soft sounds which are not of interest to the wearer, such as internally generated noise or very low level environmental sounds. Amplification of such sounds can be annoying to the hearing aid wearer in quiet situations.

Both expansion and WDRC can be illustrated by input/output curves or gain curves. If the gain of a hearing aid with WDRC is measured at different input levels, gain will decrease as the input level increases. Thus, the gain curve for a 50 dB SPL input will be higher than the one for a 65 dB SPL input, which in turn is higher than the one for an 80 dB SPL input. Simply put, as the input level increases above the compression kneepoint, the gain decreases.

Below the compression kneepoint, the hearing aid provides the maximum amount of gain. This is the linear portion of the gain curve, and all input levels are amplified with the same amount of gain.

But what happens when there is expansion in the hearing aid? Expansion also has a kneepoint, and it will be lower than the WDRC kneepoint and the linear gain portion in each frequency region. Sounds below the expansion kneepoints are amplified with less gain. Below the expansion kneepoint, gain increases as the input level increases. This provides the least amount of gain for very low input levels, for internal hearing aid noise and external noise such as fans. In this way, expansion is the opposite of compression.

Tammara Stender, Au.D., CCC-A is a Senior Audiologist at GN ReSound, where she plans and conducts clinical trials for newly developed hearing aid technology and prepares documentation for released products. Her research interests include hearing aid benefit and satisfaction, the occlusion effect and spatial localization abilities with hearing aids. She received her Master of Science degree from Vanderbilt University, and her Doctor of Audiology degree from the University of Florida.

Learn more about ReSound at www.gnresound.com or on the ReSound web channel


Tammara Stender, AuD

Senior Audiologist, GN ReSound


Related Courses

ReSound OMNIA: Introducing the Full Family
Presented by Neil Wright, AuD
Recorded Webinar
ReSound

Presenter

Neil Wright, AuD
Course: #38667Level: Introductory1 Hour
  'good format'   Read Reviews
This course will introduce the expanded line of the ReSound OMNIA family of hearing aids, including the new mini-rechargeable Receiver In the Ear, as well as the updated BTE and custom models. The presentation will highlight the benefits of the OMNIA technology, and discuss changes made to ReSound Smart Fit fitting software that are introduced as part of the update to version 1.16.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

Bridging the Gap: Bimodal Fitting Considerations for Hearing Aid Clinicians
Presented by Neil Wright, AuD
Recorded Webinar
ReSound

Presenter

Neil Wright, AuD
Course: #33557Level: Intermediate1 Hour
  'Assisting programming with patients with bimodal CI and HAs'   Read Reviews
Research has shown the benefits of bimodal stimulation in structured clinical trials, but clinical patients may require programming outside of the standard fitting flow. This presentation will discuss bimodal fitting considerations for hearing aid fitting clinicians to help patients get the most of their bimodal stimulation.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

Fitting Assistance at a Distance: ReSound Live Assistance for the Government Services Clinician
Presented by Kara Sinner, MS, CCC-A, FAAA
Recorded Webinar
ReSound

Presenter

Kara Sinner, MS, CCC-A, FAAA
Course: #35099Level: Introductory1 Hour
  'It was a good introduction to remote programming'   Read Reviews
This presentation will introduce the process for performing remote fine-tuning sessions using ReSound Assist: Live Assistance. Details will describe steps as they pertain to both the patient and the Government Services clinician.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

Auracast - The New System for Assistive Listening and Much More
Presented by Nikolai Bisgaard, M.ScEE
Recorded Webinar
ReSound

Presenter

Nikolai Bisgaard, M.ScEE
Course: #39200Level: Intermediate1 Hour
  'This technology is something that I really was interested in'   Read Reviews
This course discusses the new Bluetooth LE Audio system, which offers major new opportunities for hearing aids. Auracast broadcast audio is a new Bluetooth capability that improves audio accessibility and promotes better living through better hearing.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

Bridging the Gap: Bimodal Fitting Considerations for Government Services Hearing Aid Clinicians
Presented by Neil Wright, AuD
Recorded Webinar
ReSound

Presenter

Neil Wright, AuD
Course: #42020Level: Intermediate1 Hour
  'Easily followed and practical'   Read Reviews
Research has shown the benefits of bimodal stimulation in structured clinical trials, but clinical patients may require programming outside of the standard fitting flow. This presentation will discuss bimodal fitting considerations for hearing aid fitting clinicians to help patients get the most of their bimodal stimulation.

View this Course for FREE.
Need CEUs? Become a AudiologyOnline member to get unlimited CEUs.

Only $129/yr

Learn More

Our site uses cookies to improve your experience. By using our site, you agree to our Privacy Policy.