What Is Frequency Compression in Hearing Aids?

Frequency compression is the process of shifting sound from one pitch to another to make speech sounds more audible. Most age-related hearing loss occurs in the high-pitches, which is why women’s voices are harder to hear for those with a typical age-related hearing loss. Amplification of high-pitch speech sounds is the typical remedy, but due to the progressive deterioration of the inner ear, speech may remain unclear in cases of severe hearing loss. As a workaround, it can be helpful to shift high-pitch speech sounds down to lower pitches, where the missing consonants can be heard again.

Support for the technology

“Frequency compression [lowering] is a nifty feature that few hearing aid wearers know exist,” says Dr. Steven Sederholm, a Boynton Beach, Florida audiologist who has severe hearing loss himself. “But it’s available in many hearing aids manufactured in the past ten years or so and has become really popular in the last year and a half. Resound, Phonak, Siemens, Starkey, Widex have it. Probably a few others.”

“There are a lot of different names for it,” Senderholm continued, “frequency shifting, frequency compression, sound recover. Different companies have different ways to describe it. The technology is excellent for speech in noise, which is the biggest challenge most hearing aid wearers face, Many hearing aid wearers who could benefit from it don’t have it activated.”

Questions about effectiveness

Other audiologists aren’t quite as enthusiastic about frequency lowering. Joshua M. Alexander, an assistant professor of audiology at Purdue University in West Lafayette, Indiana, told Audiology Online: “…we don’t really know yet who will and who won’t benefit from this technology. Part of the reason is that there are only about a dozen peer-reviewed studies on modern frequency lowering techniques. Furthermore, there is a lack of consistency across studies, and sometimes within the same study, in terms of how the frequency lowering settings were chosen for each research subject.”

Dr. Alexander explains that results can also vary depending on what criteria were used. “It can make a big difference if we are comparing detection of plural ‘s’ in a controlled laboratory experiment to ratings of perceived speech intelligibility in real-world environments.”

How does it work?

To understand frequency compression, you need to understand the basics of human hearing and hearing aid amplification. An infant’s ear can perceive frequencies ranging from 20 Hz (Hertz) to 20,000 Hz; the average adult human can hear sounds between 20 Hz and 16,000 Hz. As we age, we progressively lose our ability to hear high pitch sounds. A large percent of the speech sounds needed to understand communication, like the “f”, “s”, and “th” sounds, are at 3000 Hz and above, a portion of the pitch range often affected for those with aggressive hearing loss. Unfortunately, these high-frequency consonant sounds are also some of the softest of the average speech spectrum, which means a high amount of hearing aid gain is often needed to make them audible.

Hearing aid gain is the amount of amplification, or extra volume, applied to a specific speech sounds. Gain is crucial to making sounds audible at different pitches. Too much gain may cause feedback, those screeching sounds that drive hearing aid wearers crazy, and (as mentioned above) too much amplification can cause distortions inside the inner ear, leading to reduced speech clarity. This is where frequency compression becomes our friend. Rather than over-amplify those high-pitch speech sounds, we can bring them down into another pitch region, where they can be heard with less amplification (and distortion/feedback). The downside is that the sounds may not sound quite the same. There may be a mechanical or tinny quality. This tradeoff may, or may not, be worth it depending on the individual.

Who is a candidate for frequency compression?

Hearing aid manufacturers use an algorithm to figure out when to turn this feature on. They factor in the degree of overall high-frequency hearing loss and how much gain is prescribed for the high-frequency region. Prescribed gain provides a general guideline of whether it is possible to make a given signal audible using traditional amplification.

Who may NOT be a candidate?

• New hearing aid – New hearing aid users find it difficult to adjust to the frequency-lowered sounds. That’s why frequency compression isn’t usually automatically turned on in all hearing aids. Hearing aid wearers may need proactively ask their audiologist about frequency compression to find out if it would be recommended for them.
• People with mild to moderate loss – If you have a mild or moderate hearing aid in the high frequencies it’s not a great idea to turn on frequency compression. If you can still hear high pitch sounds, there is no reason to lower the pitch of any speech sounds. However, some people who are on the borderline may want to try it to see if it helps.

How do you know your frequency compression is working?

The best procedure to determine that the frequency compression program in your hearing aids is working effectively is real-ear testing, which uses a microphone probe to examine the signal reaching the ear canal. The audiologist should measure the amplified sound with the frequency compression turned on and off, and should confirm audibility for the “s” sound. If the frequency compression helps you hear softer high-pitch consonant sounds, it is probably worth activating permanently.

Hearing Aids with Frequency Compression

There are many choices for consumers looking for frequency compression (or frequency lowering) technology. Over the last few years, many of the manufacturers have added this feature to their main product offerings. See below for a list of the latest hearing aids on with frequency compression technology.

Ask your audiologist about frequency compression

You may need to ask your audiologist about frequency compression. “A lot of clinicians don’t like to turn on frequency compression because you’re taking high-frequency energy and not amplifying it—which is the usual way–but instead shifting it to another frequency–which goes against the grain for many audiologists.” Sederholm explains. “But it’s a fantastic technology that should be explained to hearing aid wearers and turned on if appropriate.” If you think frequency compression might help you, check with your audiologist. It might make all the difference.