Most hearing losses in the mild-to-moderate range are fitted with open or vented fittings. Widex PureSound™ is designed for these users as the innovative alternative to the classic sound design in our Universal listening program. Widex PureSound™ overcomes one of the biggest contributors to the artificial sound of open and vented fittings and one of the remaining challenges for mild-to-moderate hearing losses – the comb-filter effect. Widex PureSound™ presents a very different and more natural sound, where the transparent naturalness makes a perfect impression.

Comb-Filter Effect

For open and vented fits, the direct sound that enters through and around the ear-tip mixes with the amplified sound at the ear drum. This results in a timing mismatch due to delay – the time it takes the hearing aid to process the amplified sound. This timing difference causes the comb-filter effect, where peaks and troughs form in the sound wave. In acoustic terms, we see constructive and destructive interference due to sounds mixing in phase adding together and sounds mixing out of phase cancelling each other out. The resulting sound quality has a tube-like quality to it, called the comb-filter effect, and once it is noticed, it can be very hard to accept.

The hearing aid wearer might call it a “tinny sound”. Currently this unfortunate sound artefact is one of the last major contributors to poor sound quality and is experienced to a varying degree in all commercially available hearing aids with nonclosed ear tips. Even the low delay possible in modern hearing aids is enough to cause this negative effect. A recent study on sound quality in hearing devices states that “the processing delay of 6.5 ms causing comb-filtering effects, is the main limiting factor for sound quality” (Schepker et al., 2019). Widex PureSound™, dramatically reduces the processing time through the hearing aid to below 0.5 ms, which means that the comb-filter effect is practically eliminated. By more perfectly matching the two sound sources, the experience is pure, natural, transparent and uncompromised.
Figure 3 shows group delay for different manufacturers. This clearly illustrates that Widex is already the market leader regarding group delay in our platform, while Widex PureSound™ is entirely in a league of its own. As a result, the WIDEX MOMENT™ platform is far better than any other brand in the market both in the Universal program and in the Widex PureSound™ program.

Widex Heritage – Always Lowest Delay

The entire hearing aid delay (group delay) relies on three stages: input, digital signal processing (DSP) and output stages. Widex has always designed and optimized every stage of the hearing aid to work efficiently for optimal sound quality.

INPUT: At the input stage, where we have led the market with true input technology, not only did we design A/D converters to deliver the largest linear input range in the industry; we also designed them to be ultra-efficient in terms of time delay.

DSP: We are the only manufacturer basing our signal processing core exclusively on a time-domain filter bank, allowing for extremely low delay and signal processing efficiency from the outset. All other manufacturers have built their filter banks in the frequency domain and consequently must live with the timing and delay constraints of such a design. Widex remains with a time-domain filter bank because it is the best premise for high-fidelity sound and offers the minimum time delay in processing.

OUTPUT: We can deliver an ultra-low delay output stage because of our input sampling rate of 33kHz. 33kHz was chosen as the Widex sampling rate because it maintained the maximum sound quality required by Widex design specifications. At the time, it was considered a design innovation as the Widex chipset was able to deliver this sampling rate with no detrimental effect on power consumption.

It is vital in allowing our low group delay because a high sampling rate contains fewer artefacts, which in turn means less cleaning of the signal at the output stage, allowing for an ultra-low delay output stage.

Our classic sound pathway can amplify and process sound with greater speed than any other manufacturer – this gives a sound quality advantage for all fittings. Plus, with the WIDEX MOMENT™ platform we have made special efforts to further reduce delay in the DSP stage of the hearing aid to address the mild-to-moderate hearing loss categories with the Widex ZeroDelay™ pathway. Therefore, in the WIDEX MOMENT™ platform, sound is processed through one of two available pathways:

The Widex Classic™ pathway on the WIDEX MOMENT™ platform, with heritage DSP features. In effect, all specialized signal processing algorithms are processing stages along the transmission line. A new stage, the Personal Gain Integrator, ensures perfect integration of all these differentials in perfect balance with TruAcoustics™ to ensure the perfection of individualized sound at the eardrum (see above section 2 on TruAcoustics™).

The Widex ZeroDelay™ pathway on the WIDEX MOMENT™ platform, with adapted versions of all relevant heritage features to deliver the best sound with next to no comb-filter effect. As this pathway relies on fast delivery of sound, some features are altered in nature but are still targeting signal-to-noise ratio improvements and instant feedback control. The signal processing features in the Widex ZeroDelay™ pathway mirror the intent of the Widex classic features but adapt them to the faster engine and filter gearing. It is important to stress that operating with virtually no delay does effectively change the opportunity space for feature functionality. Widex PureSound™ is a platform feature for WIDEX MOMENT™, which means it is available in all price points 110-440 and is a true alternative to our Universal program throughout the price-point range. The unique design of the Widex ZeroDelay™ pathway means that Widex PureSound™ includes a series of heritage Widex features (see features in Widex PureSound™ below). 

Significant contributors to the performance of hearing aids including Widex PureSound™ are the channels, sound classes and other price point features. The granularity of analysis and processing is determined by channels and sound classes just as in previous families. And as always, the higher the granularity, the higher the specificity of processing. 

Widex PureSound™ is available in all WIDEX MOMENT™ RIC products (and future BTE products) and promoted for open and vented fittings with appropriate hearing losses. COMPASS™ GPS will make a recommendation for Widex PureSound™ to be included in fittings for candidates within the fitting range for Widex PureSound™ shown in Figure 4. If the HCP follows this recommendation, the hearing aid will be set up with Universal (P1) and Widex PureSound™ (P2). The HCP can choose to reorder the hearing aid programs and/or set up GPS to do this by default. Widex PureSound™ operates as a substitute for Universal, but there may be situations where the more processed sound via Universal may useful. It is therefore not possible to fit a hearing aid with Widex PureSound™ alone.
Figure 4: Fitting range for Widex PureSound™

Features Running in Widex PureSound™

The premise for Widex PureSound™ is a complete rethinking of how the best sound is designed for the mild-to-moderate hearing-loss group. We have questioned the status quo and made significant changes in how sound is processed and how to make real-life listening as pure and natural as possible. It requires rethinking of the logic in signal processing, and indeed the paradigm for all classic processing schemes has been re-evaluated to determine the optimal combination of advanced features. Widex PureSound™ is unique both for Widex and the hearing industry. It is a conscious decision by Widex to take sound quality to the next level with a new design inspired by science and innovation to deliver a tailored, purposeful sound. With Widex PureSound™, nothing is quite as it was; sound is more natural, swift and perfect.

 As a result of this design innovation, three classic features are modified in the Widex PureSound™ processing. The dual-microphone adaptive directionality and the TruSound Softener both rely on extended delay in the signal pathway and are therefore not compatible with an ultrafast processing path. The Speech Enhancer is also not included in Widex PureSound™ because the time-consuming nature of this feature is counterproductive to the purpose of the new processing. In place of the Speech Enhancer, a dedicated customized noise reduction algorithm is applied. Speech intelligibility testing with WIDEX PureSound™ showed the program performed on par with the Universal program and leading competitors.

Evidence for Widex PureSound™

Figure 3 clearly shows that Widex PureSound™ is in a league of its own with respect to delay, practically eliminating the comb-filter effect and leading to a much more natural sound. However, the important question about this technical revolution is how it translates into user experience in real life. To investigate this, we conducted a series of scientific studies with Widex PureSound™ , exploring sound quality in a range of real-life situations, speech intelligibility in realistic signal-to-noise ratios and neural response to speech. Because the motivation for developing the Widex ZeroDelay™ pathway was sound quality, this was our first focus in two studies. The first study (Balling et al., 2020, see box A) was a sound quality guided walk with participants with hearing loss in the Widex PureSound™ range (both experienced and inexperienced hearing aid users) and participants with normal hearing. These participants compared two hearing aid programs: Widex PureSound™ vs. a more standard hearing aid delay. They indicated their sound quality preference in a range of settings, including quiet and noisy surroundings, listening to speech and own voice. Across all situations we observed a clear Widex PureSound™ preference, and we saw that 85% of listeners with hearing loss and 100% of listeners with normal hearing preferred Widex PureSound™ overall.

Widex PureSound™ Summary

Widex PureSound™ is a revolution in sound for mild-to-moderate hearing losses. Widex has overcome one of the last major barriers to sound quality, and the resulting sound is preferred in testing, provides robust speech-in-noise performance and shows highly faithful neural encoding. The potential for Widex PureSound™ to allow new and existing users to experience the most natural sounds will lead to improved fitting experiences, easier hearing aid acceptance and overall increased hearing aid satisfaction.
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