Ask the Audiologist

A couple of years ago the ReSound Corporation introduced a new digital signal processing hearing aid designed to further increase the ability to understand speech in a noisy environment.

The Canta 7™ hearing instrument follows the older ReSound digital 5000™ device in using Cochlea Dynamic compression to compensate for the damage done to the ear's outer hair cells, and to restore the normal amplitude relationships between sounds, but goes on to add many new features to help the understanding of speech and give greater comfort in noisy situations.

The fast acting, overlapping filters in the 14 band syllabic noise reduction system are quick enough (50 millisecond attack time and 70 millisecond release time) to be able to reduce noise between syllables, giving a smooth sound to speech while dramatically reducing the background noise, even in the same bands where speech is present. There is a natural smoothness to the noise reduction without the "up and down" volume shifting heard in some other noise reduction systems.

A hearing impaired cochlea may have hair cells with broadened frequency selectivity (a kind of "spectral smearing") which blurs speech cues and makes it hard to understand speech, even when it is amplified. The Canta 7 has a 64 band spectral enhancement FFT that emphasizes the amplitude peaks and reduces the amplitude valleys, in time periods as short as every 4 milliseconds. This increases the dynamic range of speech signals, creating more distinct and crisp speech. The overall effect of this is to sharpen up speech signals.

Note, these two features are mutually exclusive and the user must switch between them depending on whether noise reduction or speech enhancement is desired. You can think of this as giving the user comfort in noise and clarity in quiet.

But there's more. The Canta 7 also has a dual microphone system, dubbed "Digital Dynamic Directionality", that tracks background noise and reduces the microphone gain in the noise direction. This fast acting system can track moving noise sources, like people at a party, or traffic, minimizing the interference as it happens. ReSound has added a continuous self-calibration system to keep the microphones matched in amplitude and phase. Older dual microphone systems suffered from component drift and external effects, that quickly reduced their effectiveness. ReSound's calibration system acts continuously (averaging over about 100 hours of use), compensating for dirt and wax, and even hair styles. Of course, if one microphone gets too dirty, the gain of the other one must be reduced to match it, eventually hitting an adjustment limit (about 4 dB), so you still must strive to keep your hearing aids clean. (Some offices offer free clean and check clinics every three months for professional vacuum chamber cleaning of your hearing aids.)

One of the most annoying things about many hearing aids, is that they whistle when signal leaks around from the output "receiver" (down inside your ear) and gets into the microphone, causing feedback. The ReSound Canta 7 hearing instrument uses a digital feedback suppression system to create an inverted replica of the feedback signal to cancel out the whistle before it becomes audible. During the fitting process in your audiologist's office, feedback paths are detected and corrected by this signal inversion system. A second feedback management system activates automatically to reduce gain in specific bands, correcting for quick problems like when you put a phone up to your ear. These detection and cancellation systems works continuously, so you should never experience feedback for more than the second or so that it takes the system to react.

The Canta 7 comes in a complete range of case styles, from the nearly invisible CIC, all the way up to a behind the ear style based on the award winning Danavox BTE case design. Most models have 4 different memories for storing different hearing programs that are selected by pushing a button on the case (in all but the CIC, which doesn't have room for the button). These memory levels can be programed for different listening environments, like quiet conversation, or noisy office, or traffic, or music. You can choose to have fewer than 4 programs, if you just want to wear the aids and not worry about switching anything. A power BTE version with a volume control and direct audio input (as one of the 4 programs) is also available.

More recently, ReSound introduced the Canta4 and the Canta2. These newer aids are based on the same technology, but have fewer features and a lower price.

Feature Summary

Canta7 Canta4 Canta2
Digital Cochlea Dynamics 14 band Compression System Digital Cochlea Dynamics 14 band Compression System Digital Cochlea Dynamics 6 band Compression System
Digital Dynamic Directionality System Dual Microphone Directionality Max Stable Gain Curve Feedback Management
Digital matching microphones Digital Feedback Suppression Push Button Loudness Control
64 band Spectral Enhancement 14 band fast acting noise Reduction Telephone Coil Option
14 band fast acting noise reduction Up to 3 environmental programs CIC to BTE case styles
Adaptive Digital Feedback Suppression CIC to BTE case styles
Up to 4 environmental programs
CIC to Power BTE case styles