Nie-destruktiewe klankonttrekking, restourasie en spraakverheffing van Edison-fonograafsilinders

[摘要] ENGLISH ABSTRACT:Two non-destructive methods of extracting audio from Edison phonographiccylinders were investigated. A recording device with high accuracy positioning wasdesigned and manufactured. A microscopic image method was investigated first.Surface images of the cylinder were obtained using a webcamera. An audio signalwas then extracted from the width modulation. Results were not pleasing as echoescaused by intergroove modulation were perceptable. The audio also lacked resolution.The true modulation of the audio is not embedded in the width, but in the depth of thegroove. The second audio extraction method involved using a laser pick-up from acompact disc player to measure the depth of the groove. Three laser recordingmethods were investigated. The first was forward recording, that measured the depthmodulation in the recording direction of the groove. The second method, backwardrecording, was identical to forward recording with the mechanical system moving inreverse. Four recordings from different positions in the groove were combined tocreate an audio signal. This combination of recordings showed a substantialimprovement in the signal-to-noise ratio. A third recording method, transverserecording, that measured the whole depth profile of the groove was also investigated.The groove profile was then processed to an audio signal. A manual audio restorationprogram was written to replace visible sections of distorted data with betterinterpolations. Two speech enhancement methods were investigated, the first beingthe most commonly used speech enhancement method for digital audio restoration,Short-Time Spectral Attenuation (STSA). The second method is based on linearpredictive coefficient (LPC) estimation of short-time frames. The two methods wereevaluated by means of listening tests. The LPC enhancement method was preferredbecause it enhanced the intelligibility of the speech.

[发布机构] Stellenbosch University