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SOUND SMOOTHENING

Mr Mahesh, a 38yrs old is a man is a busy person and works in the clothing industry since 8yrs. He likes his profession and heads his department. His job requires him to conduct group discussions often. Since 5-6 months, he felt that he had trouble understanding during the discussions and this led to miscommunication. This ended up in lesser performance later and started to affect his productivity at work. When he discussed this with his cousin, she suggested him to see anAudiologist as soon as possible to know if there can be any hearing related problems. He then had his consultation with the Audiologist and was diagnosed to have moderate Sensorineural hearing loss in both ears. He panicked with this mere diagnosis and after the counselling with the audiologist, he felt better that he could actually start understanding speech well with the usage of hearing aids and was positive to have a trial with hearing aids for both ears.

After a brief discussion about the different models, styles and features of hearing aid, he was recommended to have a trial with RIC Pure 312 3NX devices for both ears considering his listening needs. He addressed his fears and also enquired about how he would feel when he was exposed to loud or impulse sounds. He was briefed about the features in these device and a feature which helps at these situations especially called ‘Sound Smoothening’. After about 3 days of trial with them, he revisited the audiologist and shared that he wasfeeling very satisfied and comfortable at all situations and that he wanted to start using them immediately.

Let us have a look at what this feature ‘Sound smoothening’ is all about.

Basically if you’re in the kitchen and someone drops a plate on the floor you are less likely to jump out of your skin as the hearing aid reacts immediately to loud and unexpected sounds and softens them.Background noise has long been a major issue for hearing instrument wearers. Not only does this noise often reduce speech understanding, but in many cases it creates annoyance making hearing instrument use an overall unpleasant experience.

Research has shown that new wearers of hearing instruments report background noise to become significantly more annoying after being fit with hearing instruments.

Sound smoothening is a very interesting feature in hearing aids and is a component in the speech and noise management system. It is an algorithm which reduces the annoyance of transient noises. It changes the way people feel when they use them at extremely noisy situations. People with normal hearing also find it annoying most of the times when impulse sounds are heard but Signia hearing aids technology makes the user feel drastically less irritated in such situations.

How this feature helps to solve the Annoyance problem:

It is important to consider the range of noises which the hearing instrument wearers experience in their everyday life to reduce the annoyance from noise. A potential solution to the noise annoyance problem is the implementation of digital noise reduction (DNR). Research has shown that when implemented, DNR does produce a more pleasant listening experience. When listening to speech in background noise, majority of the listeners will prefer DNR ‘ON’. Hence listeners find less levels of annoyance.

DNR Algorithms:

DNR algorithms have been modulationbased.This helps effectively in differentiating speech from broadband stationary noise and whennoise is detected as a primary signal, channel specificgain reduction occurs. Thismethod is very successful for reducing the annoyanceof any type of continuous noise. A second DNR algorithm is based on the Wiener Filter – sometimesalso referred to as “Spectral Subtraction”. This fast-acting noise reductionfilter complements the modulation-based algorithm and provides further reduction of stationary broad-bandnoise. As it is fast-acting, it is effective in reducingunwanted noise during gaps in speech.

Sound Smoothening:

First, spectral and temporalproperties of the input signal are determined by a spectro-temporal analysis. The spectral informationallows SoundSmoothing to attenuate transient highfrequency

or low-frequency sounds without affectingfrequency areas not containing transient sounds. The

temporal properties are calculated with a very highresolution and an exceptionally low processing delay(< 1ms) in order to shorten SoundSmoothing’s reactiontime on transient sounds to a minimum.

In the next stage, envelope features are extracted.These then are used to decide whether speech or non-speech sounds are present. For this purpose, the envelope features are analyzed using a speech model. Only for non-speech sounds an attenuation factor is calculated.The amount of transient gain modification is determined by the ratio of peak level to long term overall RMS level (i.e. the more transient, the more gain reduction).The maximum amount of gain reduction for transientsis adjustable as well as the detection threshold.Transient sounds with levels below detection thresholdare not attenuated by SoundSmoothing. How these parameterscan be set via the fitting software is explainedin the section “Software Fitting Options.” Finally, theoutput signal is reconstructed in the “Re-synthesis” stage.

What happens when we apply a combination of different noise reduction techniques?

Continuous sounds also can be annoying or may cause increased listening effort when simultaneously present with speech. An ideal noise management system will combine various DNR algorithms: modulation based noise reduction, Wiener filter and Sound Smoothing. Whereas modulation based DNR (“Noise reduction”) is very efficient when only stationary noise is present, the Wiener Filter (“Speech enhancement”) takes over as soon as speech and noise are simultaneously present. Finally, SoundSmoothing reduces non-stationary, transient noises, whether or not speech is present.All these noise reduction techniques efficiently reduce the amount of noise, but do not degrade the sound quality of speech.This is the result when we combine different noise reduction techniques.

A research project in NAL, Australia for SoundSmoothing for Different Environmental sounds found that astrong preference was chosen for SoundSmoothing for transient signals. For all noises with a relatively short duration, SoundSmoothing “On” was preferred by the majority of listeners, in most cases by a very large margin.

Are there any adverse effects of Sound smoothening?

As mentioned earlier, SoundSmoothing is very positive. Whenever new signal processing is introduced, however, it is critical to question, if there are any possible negative effects for the wearer when the processing is implemented. With the Sound Smoothing algorithm, it is necessary to confirm laboratory data with regards to two important listening conditions: SoundSmoothing does not affect speech understanding and auditory localization.

To examine the effects of SoundSmoothing on speech understanding, research at the National Acoustic Laboratories conducted aided speech intelligibility testing using the BKB sentences in background noise (paper rustling and cutlery). Testing was conducted for SoundSmoothing “On” versus SoundSmoothing “Off.” The results showed no significant effect of SoundSmoothing (p = 0.85). That is, as expected, there was no negative effect for speech understanding when the SoundSmoothing algorithm was used.

Auditory localization testing also was conducted at the National Acoustic Laboratories. Since SoundSmoothing reduces the slope of the acoustic envelope (to effectively reduce annoyance of transient noise) this research was conducted to investigate whether this signal alteration distorted the spatial location of the signal for the hearing instrument wearer. Localization performance was assessed with SoundSmoothing “On” versus SoundSmoothing “Off” using hammering as stimulus. The localization RMS errors revealed that as a group, there was no significant difference in localization ability as a function of the algorithm turned “On” or “Off” (p > 0.33).

In addition to the laboratory findings at NAL, subjects from another study conducted at Giessen (see next section) rated localization of signals in everyday life the same for SoundSmoothing “On” versus “Off,” indicating that SoundSmoothing has no adverse effect on localization.

SOME FITTING GUIDELINES:

As discussed, SoundSmoothing is an efficient new DNR algorithm that addresses an important concern of the hearing instrument wearer. Some general guidelines regarding the fitting of this algorithm, and patient counseling related to its processing are as follows:

1. SoundSmoothing can be used in conjunction with other DNR processing, or it can be used independently. It is an enhancement, not a replacement for the more traditional DNR techniques that also have proven patient beneficial.

2. There is no specific audiometric profile for the SoundSmoothing algorithm. If transient environmental noise is audible, as it is for nearly all hearing instrument wearers, then it would be expected that SoundSmoothing would reduce the annoyance of these signals.

3. Research has shown that in general both new hearing instrument wearers and experienced wearers will obtain listening benefit from the SoundSmoothing processing. More specifically, results from clinical studies suggest that first time wearers may benefit even more than experienced wearers.

4. There is no negative impact of the SoundSmoothing algorithm, hence, it should be considered routinely for all hearing instrument wearers.

5. Because SoundSmoothing is designed to be sensitive to abrupt signals, the hearing instrument wearer will only notice the benefit of SoundSmoothing when such signals are present. To demonstrate the advantages of SoundSmoothing, therefore, it is recommended that the dispenser presents annoying abrupt sound samples (e.g. hand clapping) to the prospective hearing instrument wearer. Paired comparisons using SoundSmoothing “On” versus SoundSmoothing “Off” in two programs as were used in the research findings previously described may be one such technique for demonstration.

Sounds below the detection threshold are not affected by SoundSmoothing. This is employed to ensure that very soft transient signals – which typically are not very annoying and often carry important information – are audible (e.g. the ticking of the clock will not activate SoundSmoothing).

Fine Tuning:

 For patients who desire less reduction/more audibility of very soft transient sounds (i.e. clock ticking), reduce the setting. For patients who are highly bothered by transient sounds (e.g. door slamming, cutlery) increase the setting (e.g. max).

Sound Smoothening is compactible with the following hearing aids:

  1. Silk 2PX Click
  2. Insio 2PX
  3. BTE Motion P/SP 2PX
  4. RIC Pure 2PX
  5. Cellion 2PX
  6. Insio 3PX (1 adjustment step)
  7. BTE Motion SP 3PX (1 adjustment step)
  8. RIC Pure 3PX (1 adjustment step)
  9. Insio 5PX (3 adjustment steps)
  10. BTE Motion SP 5PX (3 adjustment steps)
  11. Insio 7PX (3 adjustment steps)
  12. BTE Motion SP 7PX (3 adjustment steps)
  13. Insio 3NX (1 adjustment step)
  14. BTE Motion 13P 3NX (1 adjustment step)
  15. BTE Motion 13 3NX (1 adjustment step)
  16. RIC Pure 312 3NX (1 adjustment step)
  17. RIC Pure 13 3NX (1 adjustment step)
  18. Insio 5NX (3 adjustment steps)
  19. BTE Motion 13P 5NX (3 adjustment steps)
  20. BTE Motion 13 5NX (3 adjustment steps)
  21. RIC Pure 312 5NX (3 adjustment steps)
  22. RIC Pure 13 5NX (3 adjustment steps)
  23. Insio 7NX (3 adjustment steps)
  24. BTE Motion 13P 7NX (3 adjustment steps)
  25. BTE Motion 13 7NX (3 adjustment steps)
  26. RIC Pure 312 7NX (3 adjustment steps)
  27. RIC Pure 13 7NX (3 adjustment steps)
  28. RIC Pure Charge and GO 3NX (1 adjustment step)
  29. RIC Pure Charge and GO 5/7NX(3 adjustment steps)
  30. BTE Motion Charge and GO 3NX (1 adjustment step)
  31. BTE Motion Charge and GO 5/7NX (3 adjustment steps)
  32. Styletto 3 (1 adjustment step)
  33. Styletto 5/7 (3 adjustment steps)

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