AVR Sonovation, Widex and Phonak all use an approach called Frequency Lowering. Each company simply moves high frequency information to a lower frequency-- in a different manner, however.
The rationale behind this approach is that most hearing loss is worse in higher frequencies than lower frequencies. By shifting sounds to a lower frequency most patients can more easily hear that sound.
There are some caveats to this process. For instance, shifting a sound down in frequency changes sound quality-an “S” may become an “SH”. People also use the “distance” between different frequencies as a cue for understanding, this processing changes the relationship between sounds. For these reasons people often experience an acclimatization period before they adapt to the processing.
AVR was the first company to bring this processing mainstream. They targeted severe-to-profound hearing loss and “left corner” audiograms. For some people the AVR products were very successful, for others the sound quality was intolerable. This system was very aggressive and shifted frequencies dramatically.
The current strategies take a conservative approach. Very high frequencies are shifted lower but frequencies below a certain threshold (e.g. 4,000 Hz) are left untouched.
Widex was next to re-introduce this processing with their Audibility Extender. The Audibility extender uses a frequency transposition approach. They have done a good job of routinely publishing data about the behavior and benefits of the transposition approach.
Phonak followed with Sound Recover. This is a frequency compression strategy. They have been introducing field studies and have validated the use of Sound Recover in children with a recent publication from a pediatric group in Ontario. The difference between Phonak’s application and the others on the market mostly lies in the audiograms they target. Phonak will introduce some frequency compression with thresholds as low as 60 dBHL. This means that many fittings could have some amount of frequency compression.
There isn’t an expectation that either frequency compression or transposition is a preferred option. They both reach similar goals. Currently the main difference is the fact that moderate hearing loss is being targeted by Phonak’s strategy.
I am of the opinion that this technology will become a mainstay in hearing aids. However, I think we need to do more work to understand when it should be implemented. If a patient has aidable hearing we should not be removing acoustic cues by lowering them. We should also avoid using these technologies to minimize feedback or fitting difficulties.
This is an interesting topic that will, no doubt, continue to receive attention.
