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Frequency Compression

What Is Frequency Compression [Lowering] in Hearing Aids?

Hearing aids are now so sophisticated that they have features hardly anyone but audiologists are aware of, much less understand. Most of us just want to put them on and be able to hear, but like any device, the more you know the more you can benefit. This is as true of hearing aids as it is of smartphones and computers. In fact, the latest hearing aids are mini-computers.

“Frequency [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, frequency shifting, frequency compression, sound recover. Different companies have different ways to describe it. It’s 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.”

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.”

Basically, frequency lowering 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-frequency end of the spectrum, which is why women’s voices are harder to hear for those with a typical age-related hearing loss. You can try to amplify high-frequency speech sounds for severe hearing loss but, due to distortion inside the inner ear, amplified speech may be unclear. By shifting those sounds to low frequency, speech may become clearer.

However, frequency lowering is not an automatic feature. It has to be turned on, which means you should ask your audiologist about it. “A lot of clinicians don’t like to turn compression on 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.”

How and why does it Work?

To understand frequency lowering, 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 lowering 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 is probably NOT a candidate?

  • New hearing aid – New hearing aid users find it difficult to adjust to the frequency-lowered sounds. That’s why frequency lowering isn’t usually automatically turned on in all hearing aids. Hearing aid wearers may need proactively ask their audiologist about frequency lowering 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 lowering. 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.

Popular 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 most popular hearing aids on Hearing Tracker with this technology.

Erica Manfred

Erica Manfred

Erica writes the Aging with Geekitude column for Books: Interview with a Jewish Vampire; He’s History You’re Not


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  • Dana Mulvany

    I’ve been using frequency lowering since the late 1990s, starting with the AVR ImpaCt. I recently started using the Phone Brio 675 from Costco, which uses the SoundRecover2 algorithm.

    The AVR ImpaCt brought my speech discrimination for single words up at least 36% to 80%, even though there was a gap at about 1500 Hz where I heard no sound. My hearing loss is profound at 1000 Hz and higher. I haven’t yet had my speech comprehension formally tested with the Brio.

    It does take a long time to learn the new sounds (especially without training), but frequency comprehension is clearly worth it for me. I get much more audibility for high frequency sounds, including consonants. Some alerting sounds are much louder than they would be otherwise, like those for the microwave, toaster oven, smoke alarms, and seat belt. Even alerting sounds from my smart phone are louder.

    I think it’s terrific this technology exists. I’m wondering how to get more audiologists to utilize it! Sadly, the pamphlet for the Brio 675 doesn’t even mention it has the SoundRecover2 algorithm, though, and it doesn’t explain that this is much better for people with ski slope hearing loss than the original algorithm was.