What is the best way to assess non-linear frequency compression (NFC)?
After you have met targets across as broad a bandwidth as possible, turn Non-linear Frequency Compression (NFC) on. The weakest settings that result in benefit should be applied. Excessive compression should be avoided. There are behavioral and electroacoustic tests available to optimize and validate the strength of the NFC settings. Best practices would dictate that clinicians optimize and verify SoundRecover electroacoustically using speech stimuli available in newer real-ear test systems. Then, if possible, behavioral measures should be used to validate the settings with improved performance.
Behavioral Speech Tests. Since SoundRecover is designed to only impact the highest-frequency speech sounds, standard speech tests are generally not sensitive to its effects. The UWO Plurals and Ling-6 sound test package was developed by Susan Scollie and Danielle Glista at the University of Western Ontario (Scollie, Glista, Tenhaaf, Dunn, Malandrino, et al., 2012; Glista & Scollie, 2012). The Phoneme Perception Test (PPT) was developed by researchers at Phonak. The UWO Ling-6 test, Plurals test and the PPT have been shown in multiple published peer-reviewed studies to be sensitive to SoundRecover. These tests are available from Phonak and can be used to optimize SoundRecover parameters and document that amplification goals have been met.
The Plurals test is only appropriate for English speakers and can be used with children down to four years of age. With these speech-based tests, the clinician seeks to improve audibility of high-frequency sounds like /s/ without creating confusions, for example, between /s/ and /sh/. The PPT is language independent and allows assessment of high-frequency detection, distinction and recognition. In the closed-set recognition test, the patient’s high-frequency consonant recognition is assessed. The distinction test allows clinicians to assess confusions between sounds like /s/ and /sh/.
Measuring aided thresholds in the booth can also be useful to assess a patient’s access to high frequencies. When doing such functional gain testing with modern hearing instruments, it is recommended to use warbled tones and an ascending method of establishing threshold. The PPT is available in Phonak Target Software 3.2
The UWO Plurals test and calibrated Ling-6 Sound test package is available from Phonak. Please reference part number 041-1418 when ordering.
Electroacoustic Tests. The speech band stimuli available in the AudioScan Verifit and the calibrated Ling-6 stimuli available in the GN Otometrics Aurical equipment can be very useful in determining the optimal SoundRecover settings. The live speech mode can also help assess audibility and overlap of the /s/ and /sh/ sounds. Settings should to be adjusted to maximize audibility for /s/ without causing excessive overlap (and hence confusion) with /sh/.
For a complete guide to verification of NFC with the AudioScan Verifit, download the following guidelines developed by Glista and Scollie (2009) at UWO: http://www.phonakpro.com/com/b2b/en/evidence/topics/soundrecover.html
This Ask the Expert was taken from the article and text course, Sound Bytes on SoundRecover – view the complete article for more information.
Glista, D., & Scollie, S. (2009). Pediatric verification considerations for instruments with SoundRecover (non-linear frequency compression) using the latest Audioscan Verifit® tests. National Centre for Audiology, University of Western Ontario, Canada. Retrieved from http://www.phonakpro.com/com/b2b/en/evidence/topics/soundrecover.html
Scollie, S., Glista, D., Tenhaaf, J., Dunn, A., Malandrino, A., Keene, K., et al. (2012). Stimuli and normative data for detection of Ling-6 sounds in hearing level. American Journal of Audiology, 21(2), 232-241. doi:10.1044/1059-0889(2012/12-0020).