Magazine article American Cinematographer

Cinema Workshop

Magazine article American Cinematographer

Cinema Workshop

Article excerpt

AUDIO BASICS "dbx" PROCESS

The "dbx" type noise-reduction system is, in reality, a dynamic range expander. Its circuits allow the tape to accept almost twice the normal dynamic ratio. Under most circumstances this also translates into a major reduction in residual tape noise. The benefits of such a system should be obvious to the studio multi-track recordist who must cope with the cumulative noise problem associated with multiple-track mixdowns. Likewise, a classical concert recordist can surely appreciate a dynamic range of 90 dB. (No longer must he live with the guilt of performing those cardinal sins of limiting peaks and riding gain.)

The motion picture soundman benefits from the "dbx" system in a slightly different manner. The biggest problem facing the location motion picture recordist is the unexpected. Particularly on documentary and industrial films, it is difficult to predetermine exactly what the sound will be during the actual take. If levels are set close to 0 dB to gain the best signal-to-noise ratio, most assuredly someone will raise his voice or yell once the take has begun, resulting in a 15 dB overload of the tape. The problem is even more acute for documentary or news style filming. Usually employing a Sennheiser 815 shotgun or similar microphone, the documentary soundman must cover an entire group of people with just one microphone. It is almost impossible to ride gain during the conversation as it shifts back and forth from persons close to the mike who speak loudly, to soft-spoken people (who are invariably farthest from the microphone.) The soundman usually compromises, or attempts to ride gain, but inevitably some loud voices will distort or some soft sections will be lost to the noise, and the net result will be a disaster. In almost all cases the swishing effect of gain riding will be heard, as the soundman can't possibly react instantaneously to level changes.

The "dbx", under these circumstances, is a godsend. The technique I use with the "dbx" is quite simple and the results consistently excellent. The recordist adjusts the level in such a way that the loudest peaks normally encountered do not exceed -10 dB. The Nagra or similar professional recorder is capable of delivering clean sound up to a recording level of +4 or +5 dB on the modulometer, when used with the newer tape formulations. …

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