耳栓型電気音響変換器によるバイノーラル録音・再生方式に関する基礎的検討

摘要

Individual HRTFs are almost universally measured with blocked or partially blocked ear canals. However, accuracy of frequency response at the eardrum is essential for correct localization with binaural hearing, that is to say "record the sound pressure at the eardrum of a listener and then reproduce the exact same sound pressure on playback". Therefore, a probe (a soft silicon medical tubing; the internal diameter 0.5mm, external diameter lmm and length 42mm) microphone (Knowles TO-30031) was developed that allows comfortable measurements at the eardrum. The compact probe microphone can sit very close to the eardrum with no discomfort, and no disturbance of normal hearing. In this paper, an earplug type earphone system for a virtual reality system was proposed, and individual earplug type earphone equalization is obtained in the same way. The sound pressure levels at the 11 listener's eardrums as a function of frequency were measured, and constructed an inverse filter (adaptive filter) for the earplug type earphone. The results suggest that individual inverse-filtering characteristics shall be designed for a virtual reality system.%従来個人の頭部伝達関数は，音響的に剛な耳型を挿入して両耳の入口を塞ぎ，その表面上の音圧を計測している．しかし，本質的に鼓膜位置までの伝達関数によりバイノーラル録音・再生方式が正確な頭外定位を実現する．本論文では，超小型のブロープマイクロホンロホン（Knowles TO-30031マイクロホンにソフトシリコンチューブ内径0.5mm，外形1mm，および長さ42mmを取り付けた）を開発し，自由音場における鼓膜位置の音圧特性を基準信号として，外耳道が閉塞した耳栓型イヤホンシステムの鼓膜位置音圧特性を一致させるための適応型逆フィルタ特性を11孝-の被験者について測定した．その結果から，適応フィルタ特性は高周波数帯域において大きな個人差が観測され，二次元バイノーラルシステムには個人個人の逆フィルタ特性を設計する必要性が示唆された．