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In the mid-1920s, records made by mechanical recording method were used to record and restore sound for audio films. For example, the audio feature films don Juan (1926) and jazz singer (1927) made in the United States are recorded mechanically. China's earliest audio feature films "singing girl red peony" and "beauty Yu" were also recorded in this way. Although mechanical recording played a certain role in the early stage of the development of sound films, because records and films are separated, there is often a phenomenon that sound and picture are not synchronized when they are shown in cinemas. Sometimes the picture has already been played, and the sound on the record continues.
Optical recording

As early as the early stage of film development, many people put forward the imagination of using film to record and return sound. It was not until the early 1930s that the optical recording method was successfully applied to film. The earliest feature film produced by optical recording method was the seven heavy days (1937) in the United States. The earliest audio feature films made by optical recording in China include "green after rain" and "spring in the song field". By the 1980s, the vocal cords in general film reproduction were still recorded optically. In film reproduction, it can be seen that there are traces recording sound on one side of the picture, which is called optical sound trace or vocal cord.
Optical recording的進(jìn)程，是把傳聲器所拾取的聲響轉(zhuǎn)換為相應(yīng)的模仿電信號，再經(jīng)過音頻放大器把它放大到足以使光－電調(diào)幅器起作用的程度，以形成可記載的模仿光信號。光－電調(diào)幅器是光學(xué)錄音的要害部件，它把聲響的模仿電信號轉(zhuǎn)換成聲響的模仿光信號，并使用膠片對不同曝光量發(fā)生不同感光密度的特性，把聲響記載下來。對經(jīng)過錄音的膠片進(jìn)行顯影、定影、沖洗加工之后，就能顯示出感光密度不同或感光寬度不同的光學(xué)聲帶。和機(jī)械錄音比較，光學(xué)錄音的優(yōu)越性在于它所錄制的音域范圍較大；它和電影攝影所用的媒介都是感光材料，可以和畫面一起印在復(fù)制上，這種辦法既降低了制造成本、確保了聲響質(zhì)量，又使放映時的聲畫同步。
Optical recording改進(jìn)了有聲電影。前期的有聲電影幾乎全部是選用光學(xué)錄音的。50年代中期曾經(jīng)，我國的電影出產(chǎn)基本上也選用這種辦法。但是，光學(xué)錄音也有不足之處：①錄音后的感光膠片要進(jìn)行沖洗，才干得到聲帶底片，制造進(jìn)程比較復(fù)雜。②復(fù)制上的聲帶也象畫面相同需要從錄音底片上印制出聲帶正片才干還音，所以光學(xué)錄音不能立即還音，不能及時查看錄音效果。③感光膠片的聲帶上如有臟點或機(jī)械劃傷，就會發(fā)生噪聲，影響聲響質(zhì)量。④感光膠片必須在黑私自操作，工作不方便。⑤因為第②條缺點和剪接的需要，用的膠片許多，增大了制造成本。
Article source: Jiangmen recording production http://singaporeferragamo.com