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

Van der Westhuizen, Ewald (2003-12)

Thesis (MScEng)--University of Stellenbosch, 2003.

Thesis

ENGLISH ABSTRACT: Two non-destructive methods of extracting audio from Edison phonographic cylinders were investigated. A recording device with high accuracy positioning was designed and manufactured. A microscopic image method was investigated first. Surface images of the cylinder were obtained using a webcamera. An audio signal was then extracted from the width modulation. Results were not pleasing as echoes caused 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 the groove. The second audio extraction method involved using a laser pick-up from a compact disc player to measure the depth of the groove. Three laser recording methods were investigated. The first was forward recording, that measured the depth modulation in the recording direction of the groove. The second method, backward recording, was identical to forward recording with the mechanical system moving in reverse. Four recordings from different positions in the groove were combined to create an audio signal. This combination of recordings showed a substantial improvement in the signal-to-noise ratio. A third recording method, transverse recording, 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 restoration program was written to replace visible sections of distorted data with better interpolations. Two speech enhancement methods were investigated, the first being the most commonly used speech enhancement method for digital audio restoration, Short-Time Spectral Attenuation (STSA). The second method is based on linear predictive coefficient (LPC) estimation of short-time frames. The two methods were evaluated by means of listening tests. The LPC enhancement method was preferred because it enhanced the intelligibility of the speech.

AFRIKAANSE OPSOMMING: Twee nie-destruktiewe metodes om klank van Edison-fonograafsilinders te onttrek, is ondersoek. 'n Opneemtoestel, wat die silinders met baie hoë akkuraatheid posisioneer, IS ontwerp en vervaardig. 'n Mikroskopiese beeldrnetode IS as eerste klankonttrekkingsmetode ondersoek. Mikroskopiese beelde is met 'n webkamera van die silinderoppervlak geneem. Klank is vanuit die wydtemodulasie sigbaar in die beelde onttrek. Resultate was nie bevredigend nie weens groefintermodulasie-eggo's en 'n tekort aan resolusie. Die ware modulasie van die klank is nie in die wydte van die groefie gegraveer nie, maar in die diepte. Die tweede klankonttrekkingsmetode gebruik 'n aangepaste lasersensor van 'n CD-speler om die dieptemodulasie van die groefie te meet. Drie laseropneemmetodes is ondersoek. Die eerste is voorwaartse opname, wat die dieptemodulasie in die opneemrigting van die groefie meet. 'n Tweede opneemmetode, truwaartse opname, is identies aan voorwaartse opname, behalwe dat die meganiese stelsel in trurat beweeg. Vier opnames vanuit verskillende posisies in die groefbreedte is gekombineer om 'n klanksein te vorm. Die kombinasie van vier opnames toon 'n beduidende verbetering op die sein-tot-ruis-verhouding. Dit het aanleiding gegee tot die derde opneemmetode, dwarsskandering, wat die hele profiel van die groef meet. Die groefprofiel word dan verwerk tot 'n klanksein. 'n Handoudiorestourasieprogram is geskryf om sigbare verwringing in die klanksein met beter interpolasies te vervang. Twee spraakverheffingsmetodes is ondersoek. Short- Time Spectral Attenuation (STSA) is die mees gebruikte metode vir oudiorestourasie. 'n Tweede spraakverheffingsmetode wat van 'n lineêre voorspellingskoëffisiëntafskatting (LPC-afskatting) van korttydraampies gebruik maak, is ook toegepas. Die twee metodes is deur luistertoetse teen mekaar opgeweeg. Die LPCmetode is verkies aangesien dit die verstaanbaarheid van die spraak beter behoue laat bly.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/49772
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