樹莓派微電腦音效之實作與研究

本研究範圍為使用樹莓派微電腦實現動態範圍控制，其為音訊處理重點之一。音量動態範圍過大的音樂或影片播放時，常為人所詬病之處在於音量大時常會造成驚嚇，音量小如電影對白常需手動調整音量才能聽清楚。雖然保留原始音效效果才能忠於原始藝術呈現，但對於廣播及家庭視聽用途而言，動態範圍縮小過後的音訊更具實用及普遍性質。本論文旨在透過樹莓派微電腦搭配音效模組，輔以適當系統軟體組態以實作具有均衡響度效果的音訊播放裝置。藉由樹莓派OS內建的ALSA音效驅動程式架構、LADSPA音效外掛及Bash指令層腳本流程控制功能，加上第三方套件如SoX 與BC處理運算後，本論文實現了類似微軟視窗作業平台音效的均衡響度(Loudness Equalization)效果。雖然雜訊抑制性能仍有改善空間，作者乃希望透過本論文的呈獻以拋磚引玉，吸引更多音響愛好者投入社群版本的均衡響度裝置製作，期望以其零組件方便取得的特性及較低製作技術門檻而具有市場競爭性。如此一來，高檔音效不再只是少數音響廠商的專利。本論文之音效處理技術亦可廣泛應用於各種與音訊相關之產品。未來待控制介面完善後，可用於物聯網等相關裝置。

關鍵字

樹莓派；音效；均衡響度

並列摘要

The scope of this thesis lies in realizing dynamic range control of audio using Raspberry Pi micro-computer. Audio volume control is an important factor in audio processing. In case the dynamic range of a piece of music or a segment of video is too wide, it is often being criticized as there are shocks experienced for the high-volume parts, or it is too quiet for the audience to perceive details like dialogues. Though the preservation of the original sound effect is a respect to the original author’s intention, but for broadcasting and home entertainment use it is more pervasive and useful after applying a reduced dynamic range. This thesis is aimed to use a Raspberry Pi micro-computer with a sound card module, helped with appropriate system software configuration to implement an audio playback device with the volume normalization effect. Through Raspbian, a bundled operating system package of Raspberry Pi, one can have the ALSA sound driver architecture, LADSPA audio plugins and Bash shell’s flow control, plus third-party tools like SoX and BC. When combined altogether after a chain of computing process, this thesis provides the like of loudness equalization function, a feature on Microsoft® Windows® platform. Even though there is room for improvement in noise removal techniques, the intention is to attract more people of hi-fi enthusiasts getting involved in making a community edition of loudness equalization device, hoping through Raspberry Pi’s high availability and lesser efforts for implementation, one can find its competitiveness in the very consumer market. Therefore, people will be free from the patent control of specific sound drive vendors. The techniques used in this thesis can also be applied to any acoustic products. In the future after the control interface has been developed, the device can be an example in the scope of Internet of Things (IoT).