Chapter 30: Surround Concepts

Pro Tools HD-series and MIX-series systems support multichannel mixing for surround sound.

How to Use These Chapters

This part of the guide describes multichannel mixing for surround sound with Pro Tools.

These sections supplement the basic Pro Tools information provided elsewhere in the

Pro Tools Reference Guide.

If you are new to surround mixing, read the remaining sections of this chapter for an introduction to surround terminology and concepts.

If you already have experience with surround mixing, mastering, and monitoring, this chapter can be skipped. Operational instructions for

Pro Tools surround features begin in

Chapter 31, “Pro Tools Setup for Surround.”

Mixing Formats and Surround

Formats

When running Pro Tools version 5.1 or higher with the Surround Mixer plug-in, Pro Tools HDseries and MIX-series systems let you mix in 3- to 8-channel formats, in addition to standard mono and stereo.

Supported mixing formats include Mono, Stereo, LCR, Quad, LCRS, 5.0, 5.1, 6.0, 6.1, 7.0, and

7.1.

Surround formats include Dolby Surround

(Pro Logic), Dolby Digital, DTS, and SDDS.

Pro Tools does not provide its own surround format processing, and requires appropriate plugins (such as Dolby Surround Tools ™ ) or hardware to provide Dolby surround encoding and decoding.

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Pro Tools Mixing Formats

See also “5.1 Track Layouts, Routing, and Metering” on page 512.

Table 31. Multichannel Mixing and Surround Formats

Speaker Channels Multichannel

Mixing Format

Surround Format

1 Mono

2

Channels and Track Layout

C

3

4

4

LCR

Quad

LCRS

Cinema Stereo

Quadraphonic

Dolby Surround

(Pro Logic)

L C R

L R Lr Rr

L C R S

6

6

5.1

5.1

Film (Pro Tools default), for Dolby

Digital

SMPTE/ITU

(Control|24)

L C R Ls Rs LFE

L R C LFE Ls Rs

6 5.1

6.1

DTS (ProControl)

Dolby Surround EX

L R Ls Rs C LFE

L C R Ls Cs Rs LFE 7

8 7.1 SDDS L Lc C Rc R Ls Rs LFE

Legend: L = Left; R = Right; C = Center, S = surround (mono); Ls = Left Surround; Rs = Right Surround;

Lc = Left Center; Rc = Right Center; Cs = Center Surround; Lr = Left Rear; Rr = Right Rear;

LFE = Low Frequency Effects (handled by a sub-woofer or bass management systems)

Speaker Layouts

Figure 33 on page 499 illustrates the speaker arrangements of each surround format. Speaker place-

ment for each format is approximate. For proper placement, alignment, and calibration of surround monitoring systems, consult the documentation that came with your speakers and other monitoring equipment. Placement of speakers is crucial to accurate monitoring of any mix, but this is especially true with multichannel mixing for surround sound.

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L

L

Ls

Mono

L

Lr

Quad

2+2

Quadraphonic

R

Rr

Stereo

C

5.1

for DTS, Dolby Digital

R

Rs

Sub

LCR

L C R

LCRS

3+1 for Dolby Surround

S

Often split to a pair of surround speakers

L C

6.1

for Dolby Surround EX

R

Ls Cs Rs

Sub

L

Ls

Lc C

7.1

for SDDS

Rc R

Rs

Figure 33. Speaker arrangement of surround formats

Sub

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Surround Monitoring

In order to monitor your current multichannel mix in a given surround format (such as DTS or

Dolby Digital), encoding and decoding equipment for that format is required. Pro Tools does not provide direct support for surround format processing, but encoding/decoding hardware or software is available from Digidesign and thirdparty manufacturers. Contact Digidesign or your dealer for information.

Proper speaker placement, studio calibration, additional surround processors, monitors, and a properly calibrated system can lessen the variables that your mix will be subjected to when the audience eventually hears it in the theater, in their home, or elsewhere.

The Importance of Speaker

Placement

It is very important that your surround monitor system be installed and configured correctly.

Proper speaker placement, angling, and level calibration are necessities for surround mixing, so consult the manufacturer of your monitor system. Several surround formats (especially all of those from Dolby as well as DTS) have very specific speaker and monitoring recommendations, so take the time to locate this information and adhere to the suggestions they provide.

For an example of a 5.1 monitor system, see

Figure 34.

L C R

Sub

30° 30°

110° 110°

Mixing position

Ls

Rs

Figure 34. Example of speaker arrangement for 5.1 mixing and monitoring (SMPTE specification). Sub placement is variable, while all other speakers should be as close to the suggested angles as possible.

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Calibrated Surround Monitoring

One of the most important things you can do is to calibrate not only Pro Tools, but also your monitoring system and other equipment.

For example, many post production facilities calibrate their Pro Tools audio interfaces for

–20 dB = 0 VU. Once Pro Tools hardware has been calibrated to unity gain, the monitoring system can be adjusted to account for anomalies in the room acoustics, speaker placement, and other variables.

Calibrating your Pro Tools system involves attenuating the input and output stages of your system. Settings and reference level vary according to the applicable standards of the current project.

Instructions for calibrating a Pro Tools

192 I/O audio interface are included with the 192 I/O documentation.

Calibrating Your Studio The first task for surround mixing should be getting your monitor speakers in proper position, alignment and calibration for accurate listening and mixing.

Speaker position and alignment will vary according to each installation, and is very specific for different speakers, manufacturers, and for each surround format. Instructions for optimal speaker location should have been provided with the speaker and monitor system, so consult the documentation provided by its manufacturer.

Proper speaker calibration ensures that your system plays back at accurately balanced levels.

This lets you compensate for any variances in speaker position, alignment, or performance.

Formats and Terminology

Some multichannel mixing formats are referred to numerically (such as 5.1 and 7.1). These numbers describe the number and type of output

(speaker) channels required for that format.

Other formats are referred to by their track layout (such as LCRS and LCR).

Surround formats are referred to by their developer and product name, such as Dolby Surround

(or Pro Logic), Dolby Digital, DTS, Dolby Surround EX, and others. Each surround format requires you to mix in a compatible mixing format. For example, both Dolby Digital and DTS are “5.1 surround formats.”

The standards for each format include more than just the number of speakers. Formats also may require specific track layout and filtering for the various channels. For example, the surround channel in Dolby Surround is band limited from 100 Hz to 7 kHz.

Surround formats also increase the importance of phase, balance, and sound placement due to the various ways in which multichannel mixes can be encoded, decoded, compressed, matrixed, or downmixed. Many publications are available on these subjects. For a listing of several sources of surround format information, see

“Where to Get More Information on Surround

Technology” on page 504.

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LCRS for Dolby Surround

Dolby Surround (Pro Logic) is a four-channel format that is one of the most widely installed consumer surround formats.

This format, which requires Dolby encoding and decoding technology, provides three fullrange front speakers left, center, and right, plus a mono surround channel (often split and monitored through pairs of satellite speakers, but a single “rear” channel nonetheless).

Surround Format Example

The goal of Dolby Surround encoding is to make a four-channel mix (LCRS) more portable, by transforming it into an encoded two-channel mix referred to as Lt/Rt. Lt and Rt represent

Left Total and Right Total, respectively. Whenever you see Lt/Rt, it refers specifically to material that has been processed by a Dolby Surround Encoder (such as the Dolby SEU4 or

Dolby Surround Tools plug-in).

The Lt/Rt mix can then be transported, transmitted, or played as a stereo mix, making it compatible with most home and theater systems. Alternately, the Lt/Rt pair can be decoded back into an LCRS mix in home theater systems where the required decoding hardware is available.

For professional results, always use professional-level products (such as the Dolby

Model SDU4 Decoder, Model DP564 Decoder, or Dolby Surround Tools plug-in) when mix monitoring. Pro Logic-equipped consumer products have auto-balancing features which, if used for mix monitoring, may contribute to inappropriate mixing decisions

5.1 for Dolby Digital and DTS

Both Dolby Digital and DTS formats are sixchannel, 5.1 formats. Both provide five fullrange speakers and a sub. These two surround formats use different track layouts, filtering, and compression as part of their specifications.

.1 Formats

The “.1” in any multichannel mix format indicates an LFE (Low Frequency Effects) track in the mix. Whenever a decimal is part of a surround format, it indicates a discrete Sub channel in the surround playback system that is intended for playback through a subwoofer speaker. For example, Dolby Digital is a 5.1 format intended for playback through systems with five full-range speakers and one subwoofer speaker. Dolby Surround EX is a 6.1 format, with six full-range speakers and one subwoofer speaker. SDDS is a

7.1 format, with seven full-range speakers and one subwoofer speaker.

Sub content will include the LFE channel of a

“.1” format mix, as well as the effects of any bass

management in the playback system. See “LFE” on page 503.

.0 Formats

The “.0” formats (5.0, 6.0, 7.0), while not associated with any specific surround formats, are useful in many mixes as sub-paths. For example, not all tracks will have content that needs to be routed to the LFE channel (the “.1” channel).

Assigning such tracks to a 5.0 path provides a

360° panner without LFE controls.

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LFE

When a decimal such as “.1” is present in the name of a surround format, it indicates the presence of an LFE channel. The LFE channel (for

Low Frequency Effects, also known as Low Frequency Enhancement) refers most often to a specific track used in production (not during playback or decoding). LFE is the “.1” component in mix formats such as 5.1 and 7.1.

The reason the LFE component is referred to as

“.1” is that unlike the other five or seven speakers, LFE is not full bandwidth (or full-range).

The LFE signal provides a discrete path for low end to the subwoofer, unaffected by bass management (if any). Low frequency effects include such things as thunder, explosions, and other bass effects.

LFE is generally used to enhance sound effects in films. There are no set rules about whether or not you must employ an LFE channel.

Pro Tools applies no filtering to LFE signals. Some delivery requirements may re-

quire filtering for the LFE track. See “Mixing

Formats and Surround Formats” on page 497 for more information.

Sub Content

When surround mixes are played back on systems that include one or more subs, subwoofer content comes from either or both of the following sources:

• All bass from all channels that is below the threshold of the bass management filter cutoff (if any)

– and –

• Audio in the LFE channel (if any)

A surround sub will play back all the lowest-frequency sounds from all of the other speaker channels, below a fixed frequency threshold.

The threshold varies among different surround

formats. See “Where to Get More Information on Surround Technology” on page 504 for a list

of surround specification resources

.

In addition to the frequency cutoffs and other specifications of each surround format, playback system variables can affect sub content. See

“Surround Playback System Variables” on page 505 for more information.

Divergence

Divergence is a surround mixing control that lets you set panning “width.” Full divergence results in discrete (or narrow) panning. Lower divergence settings result in progressively less discrete (or wider) panning.

With Full (100%) divergence, tracks can be panned exclusively, or discretely, to a single speaker. Sounds panned to a single speaker are only audible in that speaker.

When divergence is less than 100%, tracks will be audible in neighboring speakers even when panned directly to a single speaker in the grid.

Lower divergence settings result in a progressively wider source signal.

Divergence Example

To understand divergence, it can be helpful to imagine the inside of a large movie theater. This is a good example because one of the most challenging playback variables one faces in multichannel mixing is the size of the intended listening environment.

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Unlike the typical living room, movie theaters are large spaces with speakers placed widely apart. Due to distance, sounds panned discretely to the front right speaker, for example, might be inaudible in the opposite corner. To avoid this problem, variable divergence lets you control the panning width, in order to widen the sound source. This results in signals spreading into adjacent speakers, even when panned 100% to an individual speaker.

Divergence options in Pro Tools are ex-

plained in “Divergence” on page 534.

Where to Get More Information on

Surround Technology

The table below lists several sites that are good starting points for your research into the constantly evolving world of surround sound production.

Resources for surround specifications and information

Surround Specifications Web Site

Dolby Surround/Pro Logic www.dolby.com

Dolby Digital

Dolby Surround EX

DTS

SDDS

THX www.dolby.com

www.dolby.com

www.dtsonline.com

www.sony.com

www.thx.com

Surround Mixing Concepts

As in stereo mixing and mastering, the goal in surround mixing is to provide the best sounding mix to the greatest number of potential listeners. Doing so for surround mixes requires many of the same techniques used for professional stereo production, plus several unique factors that are introduced in the following sections.

Surround Format Compatibility

Pro Tools lets you mix in surround and create multichannel masters, consisting of four, six, or more tracks that comprise an LCR, 5.1, or other format mix.

◆ Whenever necessary, multichannel mixes can be transferred as discrete, unencoded, multitrack masters. Track layout requirements vary by

format (see “Importing Multichannel

I/O Setups” on page 510 for more information).

◆ Consumer playback systems don’t necessarily support every format. Downmixing occurs when a specific format mix has to be created from another. (A typical example of this is listening to a

DVD's 5.1 Dolby Digital soundtrack downmixed to stereo.)

To anticipate the effects of surround encode and decode, as well as potential downmixing, professional surround mixes are monitored through appropriate encoding and decoding processors. Monitor controller systems let engineers hear their mix through different speakers and configurations for reference, as well as compare factors such as different bass management settings and their effect.

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Surround Formats and Delivery

Mediums

Surround mixes are tailored for their specific delivery medium. Most often, this requires formatspecific encode and decode processing.

Some delivery media on which surround formats are distributed may have additional audio constraints, which could influence your work flow in Pro Tools. Dolby Digital audio on a DVD-Video disc, for example, requires a 48 kHz sampling rate. If your

Pro Tools session isn't at 48 kHz, you must sample rate convert the audio before encoding it with Dolby Digital for DVD.

Encoding and Decoding

Many surround formats utilize some form of encoding and decoding to make it practical to deliver, broadcast, and transfer the multiple channels of full-bandwidth audio they require.

◆ Encoding is the process necessary to make multichannel mixes portable and playable. In many cases, this involves taking the four, five, six, or more discrete channels resulting from a multichannel mix and converting them into a twochannel stream for broadcast (still a predominantly 2-channel medium).

◆ Decoding is the process needed to reproduce

(or unfold) the discrete surround channels from a 2-channel delivery medium.

Both encoding and decoding, no matter how refined, represent additional processing stages applied to your mix before it reaches its ultimate destination, the audience.

For example, because the Dolby Surround algorithm depends heavily on phase relationships, there is always a significant difference in a decoded LCRS output as compared to the original

LCRS mix. To account for these anomalies, engineers mixing for Dolby Surround listen through hardware encode and decode processors for reference.

Professional mixing and mastering engineers use encoders and decoders to precisely audition the effect of the encoding and decoding process, and make any adjustments necessary.

Surround Processing and Pro Tools

Pro Tools requires additional software or hardware for surround encoding, decoding, and processing. For example, the Dolby Surround

Tools ™ plug-in lets you monitor and process completely within the Pro Tools environment.

Surround Tools and other surround processing solutions are available from Digidesign and third party manufacturers. Contact your Digidesign Dealer for more information.

Surround Playback System

Variables

Different playback systems for surround sound introduce varying amounts and types of filtering, bass management, and other variables.

These include the specifications for certain surround formats, as well as options to fine-tune a system for its particular installation.

In your own studio, you know what speakers you are listening to, what their qualities are, and what your control room sounds like. What is impossible to know, however, is what speakers are in the living room, theater, or concert hall where your mix will be heard by an audience.

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Bass Management

Bass management is a function of the playback system. Bass management refers to a number of processes by which a playback system can control what will be heard through the Sub(woofer) and other channels. The purpose of bass management is to optimize low frequency reproduction and overall frequency response for your specific monitoring system. Bass management provides a way to tune bass response for variables, including room size and shape, the presence (or absence) of a subwoofer, and the frequency range of each speaker.

Filtering

In its simplest form, bass management applies high-pass filtering to the full-range speakers.

Frequencies below the filter cutoff are summed with the LFE channel (if present) and then routed to the subwoofer. Different systems may offer additional bass management processes, including:

Bass Redirection Mutes or unmutes the low-frequency signals filtered out of the full-range channels (all signals that fall below the bass management filter cutoff frequency). This is useful when the full-range speakers are truly full-range, capable of accurately reproducing bass without distorting.

Bass Extension Allows the bass (however it is derived) to be routed back through the full-range speakers. Though this may seem like a contradiction, its main purpose is to let sub content emanate from all around, rather than only from the subwoofer.

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