モバイル機器向け音声帯域拡張の開発と評価: 信号適応型低域拡張法と客観評価法の提案

摘要

We evaluate and examine the new development process when applying speech bandwidth extension which is a technique for improving the sound quality of a narrow-band speech to the mobile computing devices. First, in order to make sound quality evaluation more efficient, we bring in the simulated MOS value [1] which is effective objective evaluation rating as substitution of MOS value. Next, speech bandwidth extension technique is developed so that sound quality may be improved using simulated MOS value. In this report, we evaluate the adaptive low-frequency bandwidth extension [2] using the simulated MOS value. Finally, evaluating keeping sound quality using the simulated MOS value, the complexity and the memory size of speech bandwidth extension are reduced and it is transported to a target platform so that it may become applicable to mobile computing devices. As a result, we verified that we could realize sound quality with a difference more significant than a narrow-band speech and that it could mount in mobile computing devices supposing ARM9 in respect of both the complexity and the memory size.%狭帯域音声の音質を向上するための手法である音声帯域拡張方式を，モバイル機器に適用する際の新しい開発プロセスの評価検討を行う.はじめに，開発効率を向上させるために，音質評価において主観評価尺度MOS値の代わりとして有効な客観評価尺度である模擬MOS値[1]を利用する.次に，模擬MOS値を使って音質を高めるように音声帯域拡張手法を構築する.ここでは，信号適応型低域拡張[2]を模擬MOS値により評価する.最後に，音質を保つことを模擬MOS値で確認しながら，モバイル機器へ適用可能になるように音声帯域拡張手法の処理量とメモリ量を削減し，ターゲットプラットフォームへ移植する.結果，狭帯域音声よりも有意な差がある音質を実現でき，処理量とメモリ量からARM9を想定したモバイノレ機器へ実装できることを確認した.