The Ugly Truth about Film Sound
[In view of Grieve’s remarks, it’s best to withhold the name of the “attempted university” where our dear friend teaches film students. Ed.]
[December 2001. Originally appeared in La Folia 3:5.]
Hi-fi it ain’t, folks! My film sound students at an attempted university get upset when I reveal to them that the mono soundtrack of their precious student film has a frequency response from 80 Hz (cycles-per-second) to 8 kHz (8 thousand cycles), slightly better than AM radio, but only slightly. So what about the Dolby Stereo 35 millimeter optical tracks at the local sexplex? Try 50 Hz to 12 kHz — not CD quality by a country mile, for a couple of reasons:
1) There are only so many wiggles you can print on 35 mm film and resolve on playback. And 12 kHz is about the max!
2) The movin’ pictures are restricted by a piece of plastic with holes in it, called a screen, which both hides the front speakers and blocks off most of the high-frequency signals.
So it’s not surprising that for decades the mastering recorder for films was the mono Nagra 4.2, which arrived in 1968! It has a frequency response (factory spec) from 50 Hz to 15 kHz, about the same as FM radio. But the audible response starts to roll off at 12.5 kHz, still plenty high for 35 mm film. So much for the analog optical Dolby Stereo soundtrack.
Well, now we have Dolby Digital and Sony SDDS Digital sound, don’t we? Yes and no. The Dolby digital dots are printed between the sprocket holes on the sides of the film. And the Sony digital info is printed outside the sprocket holes, at the edge of the film. If the digital dots get trashed, there’s an automatic switchover to the Dolby analog optical track As any projectionist will tell you, after one trip through the projector, the digital dots are rendered un-readable. The sprocket holes and edges of the film are where it gets the most wear. So regardless of what it says on the marquee, you’re probably listening to the old Dolby analog track!
The exception is DTS, which is now installed in almost half the theatres in the U.S. of A. DTS has the digital information on a separate CD-ROM slaved to time code on the film’s optical track. DTS also has a rather mild 2:1 compression of the digital data. Unless the projectionist has lost the accompanying CD-ROM disc, you and enjoy full-range digital sound at the picture show.
Some financially fortunate location sound men can afford the Nagra D digital recorder, when can be set up to give you four separate channels of digital audio for dialog mixing later. Nagra has just announced their Mark II incarnation of the Nagra, which I suspect involves increasing the bits from 20 to 24. Every Nagra D recording I have heard has a steely, gritty quality that I attribute to less-than sterling op-amps. But the 20-bit Nagra D was used by Chris Newman for the Award-winning “The English Patient.” He also favors the Sennheiser 815 shotgun mic, which is a relic from the early 1960s. My life got a lot simpler when I unloaded that mic in the 70s.
Craig Dory, of Dorian Records, also swears by the Nagra D, as does John Atkinson, of Stereophile. Atkinson also uses the Bruel & Kjaer electret mics, which I have always found to be cold and clinical, except when used by Jared Sacks, of Channel Classics. Jared informed me that he uses customized power supplies for the B&Ks to warm up the coldness.
What’s used for high-end film sound is also employed for some audiophile music recordings for substantially the same reason: portability. You can heft a Nagra D with one hand and it runs all day on internal batteries. That’s quite an advantage over a 48-track Sony that may require 220-volt power.
Unfortunately for us listeners to classical CDs, there are very few options at any price available to the quality-conscious recordist. The newer magneto-optical disc recorders like the Genex seem to offer not only better audio quality but instant access and can directly download to a computer hard drive for editing.
Even though my crystal ball is seriously cracked, I predict that in a year or so we’ll see Memory Stick-type recorders come into use for film dialog recording, and possibly even for low-budget music recording. Right now Nagra sells a solid-state recorder in Europe for radio reporters, but its bandwidth is limited to 6 kHz to get even a minimum of recorded time. I think greater memory is on the way.