Jeffrey P. Fisher - Fisher Creative Group

Article: Surround Sound Basics

By Jeffrey P. Fisher

Surround allows immersing the audience in the location. Developed for film sound, adopted for TV, DTV, games, and music.
Surround sound or 5.1 comprises stereo L/R, dedicated center channel, surround or rear channel L/R, and a low frequency enhancement channel (LFE).
Projects mixed in surround collapse (or downmix) to stereo for those who don't have surround listening capabilities.

Stereo microphone techniques translate well to surround: X-Y, ORTF, Spaced Omnis, and Decca Tree. There are also dedicated surround mics such as the Holophone H2.

Surround authoring program (multi-track audio with video support)
Dolby AC-3 and/or DTS encoder
Multichannel soundcard (six output channels)
Five matching full-range speakers (self-powered a.k.a. active monitors).
One subwoofer capable of reproducing 20-120 Hz (self-powered)
Connect speakers and soundcard using short, matched cable runs. Mount speakers on rock solid surface and/or stands. Consider using Auralex MoPads for isolation. Place them away from the wall (in the free field). Make the room reasonably "dead" around the speakers (using acoustic foam) and a somewhat more "dead" room overall.

Filtered pink noise (band limited to 500 Hz to 2 kHz) at -20 dbFS RMS into each speaker.
Individual speakers read 83dBc (79 dBc TV) on SPL (c-weighted, slow)
For the LFE, use filtered pink noise (band limited to 20 Hz to 120 Hz) and set the volume of that 4-5 db higher (Works out to 10 dB higher than others).
Fletcher-Munson equal loudness is why LFE is louder (ear less sensitive to bass at lower listening levels).

The LFE is an enhancement channel for special effects. It is not for the program bass.
Bass management is the process whereby consumer playback systems route bass to the subwoofer component to make up for the lack of bass content in the satellites.
Downmixing adds center and surrounds to the stereo mix at proportions you determine when encoding AC-3. Always prepare a dedicated stereo mix.

Surround Panning = position of sound in the 5.1 speaker array (controllable over time through the authoring program).
There are no rules for mixing surround sound. Picture the soundscape as it relates to the visual and position your sounds accordingly. Decide whether to immerse your audience IN the experience or not. Constant surround is often ineffective.
Generally, put your dialog in the center speaker.
Music works in stereo or faux surround (artificial ambience in the Ls/Rs)
Use delay (or reverberation) on music, dialog, and effects and send the delayed output to the rear speakers to create a more open surround experience that envelopes the listener.

Check (and double-check) your surround mixes in a variety of settings.
Setting the dialog normalization (dialnorm) and the Dynamic Range Compression (DRC) correctly is important. Dialnorm at -31 equals no level shift in your content. DRC profiles are end user selectable.