應用phase vocoder實現卡拉OK伴唱機音效以虛擬重低音合成

Abstract

諸多的音效， 例如時間拉長、音調變高、頻率升高、顫音等音效對於音效的處理是相當重要的。許多音效可以用在家庭娛樂系統以及卡拉OK伴唱機的特殊音效實現，而這些音效大多需要藉由數位訊號處理器來實現在硬體上面。在本篇碩士論文中，將會以數位訊號處理的技巧來實現諸音效。而當我們在使用PC娛樂系統時，音訊的低頻訊號部份，常常無法在一般的桌上型喇叭上播放出來，這是由於一般的喇叭在物理條件上的限制，使得音訊的低音部分常常無法完美的被呈現出來。因此本篇碩士論文將闡述一種方法可以在普通喇叭上實現重低音的音訊，利用的是心理聲學的原理：原本無法在喇叭上完美呈現的低頻部份，可以利用產生此低頻訊號的數個諧波的總和來呈現；由於此數個諧波對於原本的低頻訊號而言是較高頻的訊號，因此是可以在普通揚聲器上播放的。同時也考慮到等響度曲線的機制，對於各諧波的權重加以計算衡量，使得利用這些不同權重的諧波總和，能夠取代原本的低頻訊號，而且對於使用者來說，會有與原本低頻幾乎一樣的感覺。實施主觀聽力實驗以驗證其效果,並且將實驗數據以統計軟體加以分析,驗證實驗結果在統計上是否具顯著性。

Audio effects, such as time stretching, pitch shifting, frequency scaling, vibrato and tremolo are indispensable in music production and performance. Some of them are available for home entertainments and Karaoke systems. These digital audio effects are accomplished through the discrete-time signal process. Concerning the poor performance of the low frequency signal in a general speaker, the virtual bass synthesis technique has been implemented to enhance the low frequency sensation without using an extra sub-woofer or damaging the speakers. Due to the physical limitation of a general speaker, the low frequency components of an audio signal can not be well performed. The solution to this problem is to generate a series related super harmonics so as to substitute the low frequency. Taking listening intensity into consideration, the equal loudness contour is proposed to determine the different weighting for the each related harmonic. Subjective listening tests were carried out to explore the performance of the sounds, and the data will be analyzed to justify the statistical significance.