AES Section Meeting Reports

San Francisco - September 18, 2007

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At AES San Francisco's September meeting, Ioan Allen presented the Egg Show, a two hour lecture, giving an overview of film sound. Allen is Senior Vice President at Dolby Labs, in San Francisco.

The meeting was held at Dolby Labs' screening room. Seventy-five people attended.

Allen began by describing some of the technical features of the Dolby screening room. The walls contain forty-five tons of sheetrock, for acoustic isolation. The noise level is claimed to be NC (Noise Criterion)-13, considerably quieter than most cinemas.

A sensation of quiet is immediately noticeable, on entering the screening room.

Allen pointed out that ventilation is the main source of background noise in cinemas.

The projection screen has a matte finish, providing the same brightness from every seat. The sound system also has uniform response, with no hot spots.

Allen showed several film clips, including one shot in a coal mine. A crossed pair of microphones was used, creating a striking sense that the viewer is in the mine.

Another clip, produced by the British post office in the 1930s, showed how mail was delivered by, and sorted on, trains. The film was recorded in mono, and also seemed remarkably real.

Film sound began in the 1930s, but lagged behind pictures in fidelity and realism for decades.

To make soundtracks seem real, sounds can be made louder and softer, can be localized, reverberated, or immediately preceded or followed by silence (as silent as possible in many cinemas). Distant, reverberant sounds can create a feeling of protected, personal space. Spatially widening sounds makes an impressive impact.

Some sounds, though seeming real, exist only in films. The sound of tires squealing, when airplanes land, known as 'wheel hits,' fits this description. Microphones placed next to airport runways pick up no such sounds. The sound can be created by combining squealing car tires, with vocal sounds of baby bears.

A rule of thumb about movie soundtracks is that if they sound poor, first try removing something. The audience can only process so much information.

A line of sight is required for dialog mikes. The mike must "see the lips," otherwise quality is greatly compromised. This explains why getting good vocal sounds from lapel mikes is often a challenge.

Documentary films before the 1960s were mainly shown in cinemas. Afterwards they were shown on television, resulting in more compressed audio, with less impact.

Allen believes few contemporary films have enough dynamic range. Real life has tremendous differences between loud and soft.

Mr. Allen's Egg Show ended with a clip from Master and Commander, which included the sounds of cannons. This demonstrated the extended low-frequency response of the screening room's sound system, and the emotive power of cinema sound.

by Paul Howard

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