Surround Sound Digital Processing FAQs

What are the limitations of low-frequency roll-off with traditional directionality?
Low frequency information can be lost if there is roll-off of amplification due to loss of audibility in this region. The partial compensation with Bass Boost does not completely restore low-frequency audibility.

Other manufacturers tout the speed of their processing. Is WARP the fastest?
WARP refers to the digital frequency analysis, and is the most efficient way to get frequency resolution that is equivalent to the auditory system. Other systems may be faster but it may result in a compromise on frequency resolution or preservation of temporal cues that contribute to localization ability.

What are the primary reasons for an improved listening experience with ReSound Alera?
a.    ReSound Alera mimics the natural ear listening experience with Warp-based processing and the Surround Sound Processor.
b.    Sound quality is improved due to the extended high frequency range to 7KHz.
c.    DFS Ultra with built-in Whistle Control reduces interruptions from feedback in a greater variety of listening situations.
d.    Environmental Optimizer II ensures comfortable listening in varying listening environments.

Is there extended bandwidth with ReSound Alera?
Yes. The bandwidth extends to 7000Hz.

Are you planning to extend the frequency range of your products in future products (i.e. out to 10K)?
Currently, our bandwidth extends to 7kHz for all products. We have been investigating implementing extended frequency ranges in our future products. Note that other manufacturers who advertise their extended bandwidth do not actually make use of it in their gain prescriptions.

How fast is the chip in the hearing instrument?
16 MHz is the CPU speed.

How fast is the data transmission?
2 megabits per second.

Why does a low-frequency roll-off occur when you activate a directional microphone?
Directional microphones are less sensitive in low frequency regions than omni-directional microphones.

What are the limitations of bass boost compensation with traditional directionality?
Bass Boost compensation is used to counter loss of far-field low-frequency sounds caused by a directional microphone. That compensation leads to over-amplifying near-field sounds (i.e., the proximity effect). The noise floor is increased, which can be very annoying for the user.

These limitations lead us to put an omnidirectional response in the low frequencies. Why is this important?
An omnidirectional response in the low frequencies for directional programs resolves the limitations of directionality with little sacrifice. Audibility and comfort are restored into the intelligibility-centered framework of directional technology.

In addition, the natural unaided ear head-related transfer function (HRTF) shows a more directional response for high frequencies than for low, which appear as a more omnidirectional response due to the decrease in head shadow effects in the low frequencies.

Why do the low and high frequencies need to be treated differently, and how does this relate to the natural ear?
In terms of localization abilities, interaural time differences (ITDs) are informative in the lower frequencies; interaural level differences (ILDs) are informative in the higher frequencies. By using a similar, fixed processing scheme for high frequencies only across a bilateral fitting, we can maintain directional benefit with preserving important ITD cues through omnidirectional processing in the lower frequencies.

In addition, the unaided head-related transfer function (HRTF) makes a distinction between high and low frequencies in terms of directionality. High frequencies are more directional, and low frequencies are more omnidirectional.

What is the importance of maintaining the natural time constants or interaural time differences (ITDs), and what are the consequences if we do not?
Natural time constants are important to spatial hearing, spatial awareness, and localization. If these time constants or interaural time differences are altered through hearing aid processing, these elements of hearing may be impaired.

In Aventa, the dispenser has the option of shifting the crossover frequency (or blending point) higher or lower. Why and when would they want to do this?
In the Aventa software, the shifting of the blending point occurs through changes to the “Directional Mix” setting. The Directional Mix setting is inversely related to the crossover frequency. A very low Directional Mix setting results in the highest blending point, and provides less directionality in the low and mid frequencies. Increasing the Directional Mix setting decreases the blending point, thereby providing more directionality in the low and mid frequencies.
If a patient complains of difficulty understanding conversation in a noisy surrounding, the Directional Mix setting should be increased. If the patient complains that the hearing instrument is too noisy in quiet situations or desires more listening comfort, then the Directional Mix setting should be decreased.  Note that because the mixing point is calculated automatically, the settings should only be changed when the patient’s needs can be clearly and accurately assessed.

When you change the directional mix setting, is there any change in the low frequency intensity?
No. Changing the directional mix will cause the hearing instrument to have a larger or smaller omnidirectional frequency range, but there is no intensity change.

How is band-split directionality different from fixed directionality?
Fixed directionality refers to the polar pattern directional response of the device; the nulls are in a fixed position with fixed directionality. Band-split directionality is the scheme where high frequencies have a directional response and low frequencies have an omnidirectional response. Fixed directionality is also processed in a band-split manner in the Alera™ product family.

Why is the concept of band-split directionality important?
Band-split directionality, due to its preservation of interaural time difference cues in the low frequencies by virtue of omnidirectional processing, is helpful in maintaining good spatial hearing and sound quality.

For what types of hearing loss might band-split directionality work best?
Band-split directionality works best with patients that have relatively good low frequency hearing sensitivity in combination with a significant high frequency sensorineural hearing loss.

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