Research on the mechanism of mildew contamination affecting the sound quality of analog tape archives

Since 1947, analog tape recording has become the main method of sound recording, and has been widely used in music dissemination, cultural popularization, scientific research, news interviews, etc. For more than 40 years, giving birth to a large number of important audio recording archives. Due to the presence of a large amount of adhesive in the tape, mildew have been found on the surface of the magnetic layer and the edges of many tapes, posing a serious threat to the long-term preservation and the sound quality of the recordings. In this paper, ATR-FTIR and SEM were used to extensively characterize the chemical and physical of magnetic tape materials. To assess the effects of mildew contamination, the common strain Penicillium and Aspergillus was used to prepare mildew corrosive samples with different coverage degrees, and the corresponding audio samples were analyzed by Praat, a professional speech analysis software. The relationship between wideband spectrogram, sound intensity contours, formants plots, center of gravity, standard deviation, skewness, kurtosis, band energy difference and coverage degree of mildew contaminated samples were analyzed. Additionally, the surface roughness and morphology of the analog tapes were observed using the laser microscopy system. Based on the above information, the mechanism by which the dual effects of mildew coverage and corrosion affect sound quality was revealed. This research provides a theoretical foundation for improved and restored strategies to mitigate mildew damage contaminated analog tape archives in the future.