音效卡肺音錄製系統可行性分析

Abstract

本研究旨在架構一可靠的音效卡擷取訊號之肺音錄製系統，其中的關鍵在於針對肺音發生的頻段進行嚴謹的可靠度分析，可靠度分析可略分為頻譜分析與相關係數演算法兩個過程，其步驟為：(1) 傅立葉轉換；(2) 頻譜平均；(3) 頻譜正規化；(4) 對齊峰值；(5) 相關係數；以及(6) 雙側相關係數演算法。本研究提出雙側相關係數演算法作為音效卡與類比對數位轉換器的相關程度比較，藉此驗證以音效卡作為肺音擷取裝置的可行性。肺音錄製系統分為硬體與軟體部份，硬體部份以指向性電容式麥克風(Beta 54, Shure, USA)接收肺音訊號，經由前置放大器傳輸到電腦。在軟體部份，以LabVIEW撰寫訊號儲存與訊號分析的功能。實驗結果可以發現，每個頻率訊號的頻譜之雙側相關係數均在 0.95 以上，顯示音效卡與多數研究群所使用的類比對數位轉換器所擷取的訊號有高度的相關性，因此以音效卡作為肺音訊號的擷取裝置是可行的。

This study is to setup a reliable recorder for lung sound. The acquisition device that most research groups employ is the analog-to-digital converters. However, sound card present in the personal computer or notebook is used in this study.. Therefore, the reliability analysis of sound card has to be examined seriously. The analysis includes two processes. One is spectrum analysis, the other is correlation. The steps are as follows: (1) Fourier transform; (2) average spectrum; (3) normalization; (4) peak regulation; (5) correlation coefficient; and (6) bilateral analysis. Bilateral analysis for correlation coefficient of spectrums from the measurements of lung sound by analog-to-digital converters and by sound card were also conducted.. The system hardware is constructed by series connection of a high directionality microphone (Beta 54, Shure, USA), a preamplifier (MIC200, Behringer, Germany), and a sound card of a personal computer (ASUS, Taiwan). The platform software for data storage and analysis is coded in LabVIEW (National Instrumentation, USA). The findings indicate that the bilateral correlation coefficients for the test frequencies of the two devices are all over 0.95. In conclusion, the sound card is feasible to be an acquisition device for lung sound.