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PERFORMANCE LIMITATIONS OF RECORDED SOUND 429
the recorded dynamic range in the print exceed the range of the projector by even a small margin, the low level passages of the film will be inaudible, since they will be drowned out by noise. To avoid the addition of an appreciable amount of distortion and of noise — which reduces the useful dynamic and frequency ranges, all printing machinery must be maintained in best operating condition. This means making certain that the light field of the printer illumination system shall be as uniform as possible throughout the printed area, both as to intensity and chromatic quality. When the printer is running, there should be a minimum of vibration of the printer lamp with respect to the optical axis of the illumination system in order to avoid the introduction of audible noise. The propulsion system of the printer must be maintained, and sprockets and gates must remain properly aligned. Because of propulsion irregularities, measurable flutter is introduced in even the best contact printer and can be observed by reproducing a print of, e.g., the 5000-cycle SMPE focus test film on a film phonograph, meanwhile observing on a cathode ray oscillograph the waveform of the wave envelope caused by flutter.
Unfortunately, most commercial film laboratories do not routinely make such tests on their equipment ; printer performance maintenance measurement is still quite crude in practice. Quite often, published data found in technical journals represent the performance of an isolated piece of equipment under noncommercial operating conditions. It represents, rather, what a particular piece of equipment is capable of doing under certain limited idealized conditions rather than what its counterparts do in practice.
The noise and distortion introduced in each transfer step is quite large and varies over rather wide limits from one laboratory to another. It varies for different machines within the same laboratory and for the same machine at different times, though to a lesser degree. It is a common experience of film users to find that there is a significant difference in sound quality between the averages of two different lots of prints made at different times from the same release negative or other preprint material.
Printer loss characteristics may be checked by printing a calibrated film such as American War Standard Film Z22.44-1946. This, with its calibration, may be obtained from the Society of Motion Picture Engineers. A comparison between the standard film and the print with both run on similar film phonographs in an A-B test with a cathode ray oscillograph used for checking waveforms will quickly show up significant