Determination of Optimum Parameters for Cochlear Implants Speech Processors by Using Objective Measures

Abstract

In a cochlear implant (CI) processor, several parameters such as channel numbers bandwidths, rectification type and cutoff frequency play an important role in acquiring enhanced speech. The effective and general purpose CI approach has been a research topic for a long time. In this study, it is aimed to determine the optimum parameters for CI users by using different channel numbers (4, 8, 12, 16 and 22), rectification types (half and full) and cutoff frequencies (200, 250, 300, 350 and 400 Hz). The CI approaches have been tested on Turkish sentences which are taken from METU database. The optimum CI structure has been tested with objective quality that weighted spectral slope (WSS) and objective intelligibility measures such as short-term objective intelligibility (STOI) and perceptual evaluation of speech quality (PESQ). Experimental results show that 400 Hz cutoff frequency, full wave rectifier and 16-channels CI approach give better quality and higher intelligibility scores than other CI approaches according to STOI, PESQ and WSS results. The proposed CI approach provides the ability to percept 91% of output vocoded Turkish speech for CI users.

Keywords

• Cochlear implant
• Vocoder
• Filter bank
• Objective intelligibility measures

Determination of Optimum Parameters for Cochlear Implants Speech Processors by Using Objective Measures

Abstract

Bir koklear implant (Kİ) işlemcisinde, kanal sayıları, bant genişlikleri, doğrultma tipi ve kesme frekansı gibi çeşitli parametreler, gelişmiş konuşma elde etmede önemli bir rol oynamaktadır. Etkili ve genel amaçlı Kİ yaklaşımı uzun süredir araştırma konusu olmuştur. Bu çalışmada, farklı kanal sayıları (4, 8, 12, 16 ve 22), doğrultma tipleri (yarım ve tam dalga) ve kesme frekansları (200, 250, 300, 350 ve 400 Hz) kullanılarak Kİ kullanıcıları için optimum parametrelerin belirlenmesi amaçlanmıştır. Kİ yaklaşımları ODTÜ veri tabanından alınan Türkçe cümleler ile test edilmiştir. Optimum Kİ yapısı, ağırlıklı spektral eğim (WSS) gibi nesnel kalite, kısa-süreli nesnel anlaşılabilirlik (STOI) ve konuşma kalitesinin algısal değerlendirmesi (PESQ) gibi nesnel anlaşılabilirlik ölçütleri ile belirlenmiştir. Deneysel sonuçlar, 400 Hz kesme frekansı, tam dalga doğrultucu ve 16-kanallı Kİ yaklaşımının STOI, PESQ ve WSS sonuçlarına göre daha kaliteli ve daha yüksek anlaşılabilirlik skorları verdiğini göstermektedir. Önerilen Kİ yaklaşımı, implant kullanıcıları için çıkış kodlu konuşmanın %91'ini algılama yeteneği sağlamaktadır.

Keywords

• Cochlear implant
• Vocoder
• Filter bank
• Objective intelligibility measures

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