Formatos Dolby

Dolby Digital

Dolby Digital is the common version containing up to six discrete channels of sound. The most elaborate mode in common usage involves five channels for normal-range speakers (20 Hz – 20,000 Hz) (right front, center, left front, right surround and left surround) and one channel (20 Hz – 120 Hz allotted audio) for the subwoofer driven low-frequency effects. Mono and stereo modes are also supported. AC-3 supports audio sample-rates up to 48 kHz. Batman Returns was the first film to use Dolby Digital technology when it premiered in theaters in Summer 1992. The Laserdisc version of Clear and Present Danger featured the first Home theater Dolby Digital mix in 1995.

This codec has several aliases, which are different names for the same codec:

* Dolby Digital
* DD (an abbreviation for Dolby Digital, often combined with channel count; for instance, DD 2.0, DD 5.1)
* AC-3 (Audio Codec 3, Advanced Codec 3, Acoustic Coder 3. These are backronyms. However, Adaptive Transform Acoustic Coding 3, or ATRAC3, is a separate format developed by Sony)[10]
* ATSC A/52 (name of the standard)[11]

Dolby Digital EX

Dolby Digital EX is similar in practice to Dolby’s earlier Pro-Logic format, which utilized matrix technology to add a center channel and single rear surround channel to stereo soundtracks. EX adds an extension to the standard 5.1 channel Dolby Digital codec in the form of matrixed rear channels, creating 6.1 or 7.1 channel output.

Dolby Digital Surround EX

The Cinema Version of “Dolby Digital EX” is called Dolby Digital Surround Ex and works the same way. Dolby Digital Surround EX was co-developed by Dolby and Lucasfilm THX in time for the release in May 1999 of Star Wars Episode I: The Phantom Menace. It provides an economical and backwards-compatible means for 5.1 soundtracks to carry a sixth, center back surround channel for improved localization of effects. The extra surround channel is matrix encoded onto the discrete Left Surround and Right Surround channels of the 5.1 mix, much like the front center channel on Dolby Pro Logic encoded stereo soundtracks. The result can be played without loss of information on standard 5.1 systems, or played in 6.1 or 7.1 on systems equipped with Surround EX decoding and additional speakers. Dolby Digital Surround EX has since been used for the Star Wars prequels on the DVD versions and also the remastered original Star Wars trilogy. A number of DVDs have Dolby Digital Surround EX audio option.

Dolby Digital Live

Dolby Digital Live (DDL) is a real-time hardware encoding technology for interactive media such as video games. It converts any audio signals on a PC or game console into a 5.1-channel 16-bit/48 KHz Dolby Digital format at 640kbps and transports it via a single S/PDIF cable.^[12] A similar technology known as DTS Connect is available from competitor DTS.

The most important benefit of this technology is that it enables the use of digital multichannel sound with consumer sound cards, which are otherwise limited to digital PCM stereo or analog multichannel. Later, HDMI introduced and supports digital multichannel PCM, but for S/PDIF, DDL and DTS Connect are the only way to support digital multichannel sound unless the sound source is already encoded by DD / DTS.

Dolby Digital Live is currently available in sound cards from manufacturers such as Creative Labs, Diamond Multimedia, TerraTec, Turtle Beach,^[13] HT OMEGA SYSTEM,^[14] Auzentech^[15] and Asus^[16] using C-Media chipsets. The SoundStorm, used for the Xbox game console and certain nForce2 motherboards, used an early form of this technology.

DDL is also available on motherboards with codecs such as Realtek‘s ALC882D,^[17] ALC888DD and ALC888H.

Since September 2008, all Creative X-Fi based sound cards support DDL (except the ‘Xtreme Audio’ and its based line such as Prodigy 7.1e, which is not capable of DDL in hardware), but X-Fi‘s case is a bit complicated.

Originally, all Creative X-Fi based sound cards did not support DDL (2005~2007). When Creative and Auzentech developed Auzentech Prelude which was the first X-Fi card to support DDL, they planned to extend DDL support to all X-Fi based sound cards (except the ‘Xtreme Audio’ line which is not capable of DDL in hardware). However, they dropped the plan because Dolby licensing would have required royalty payment for all X-Fi cards including those already sold. ^[18] In 2008 Creative released the X-Fi Titanium series of sound cards which fully supports Dolby Digital Live, while all PCI versions of Creative X-Fi still lacked support for DDL.

While they forgot about the plan, a programmer named Daniel Kawakami, who is famous for his Creative driver modifications, made a hot issue by applying Auzentech Prelude DDL module back to Creative X-Fi cards by disguising the hardware identity as Auzentech Prelude.^[19]

Creative Labs had alleged about Daniel_K that many consumers admire Daniel_K and blame Creative Labs, so begin to insist that Daniel_K had violated their intellectual property and demanded he cease distributing his modified drivers. ^[20][21][19]

Nonetheless, Creative finally made an agreement with Dolby Laboratories about Dolby license royalty by making who buy Creative X-Fi PCI cards pay the royalty instead of Creative.^[18] Based on the agreement, in September 2008, Creative began selling the “Dolby Digital Live” packs which enables Dolby Digital Live on Creative’s X-Fi PCI series of sound cards. It can be purchased and downloaded from Creative. In later, Creative added “DTS Connect” pack to the DDL pack without any additional cost. ^[22]

Dolby Digital Plus

Dolby Digital Plus (DD+ or E-AC-3 (Enhanced AC-3), and sometimes incorrectly as EC-3) is a digital audio compression scheme. It is an incompatible^[1] development of the technologies used in the earlier Dolby Digital system. E-AC-3 has a number of improvements aimed at increasing quality at a given bitrate compared with legacy Dolby Digital (AC-3). While legacy AC-3 supports up to 5 full-range audio channels at a coded bitrate of 0.640 Mbit/s, E-AC-3 supports up to 13 full range audio channels at a coded bitrate of 6.144 Mbit/s peak.

Dolby Digital Plus bitstreams are not backward compatible with legacy Dolby Digital decoders, and decoders that output audio over legacy S/PDIF connections must transcode the bitstreams to an older format such as PCM, AC-3, or DTS.

Dolby TrueHD

Dolby TrueHD is an advanced lossless multi-channel audio codec developed by Dolby Laboratories which is intended primarily for high-definition home-entertainment equipment such as Blu-ray Disc and HD DVD. It is the successor to the AC-3 Dolby Digital surround sound codec which was used as the audio standard for DVD discs. In this application, Dolby TrueHD competes with DTS-HD Master Audio, another lossless codec from Digital Theater System.

Dolby TrueHD uses Meridian Lossless Packing (MLP) as its mathematical basis for compressing audio samples. MLP was used on the earlier DVD-Audio format, but details of Dolby TrueHD and DVD-Audio differ substantially. A Dolby TrueHD bitstream can carry up to 14 discrete sound channels. Sample depths up to 24 bits/sample and audio sample rates up to 192 kHz are supported. Like the more common legacy codec Dolby Digital, Dolby TrueHD bitstreams carry program metadata. Metadata is separate from the coding format and compressed audio samples, but stores relevant information about the audio waveform. For example, dialog normalization and Dynamic range compression are controlled by metadata embedded in the TrueHD bitstream.

Dolby Facility Approval Requirements (Original em Inglês)

6.0 Technical Requirements for Studios to Obtain Dolby Certification

6.1. The first essential requirement for the dubbing theatre is to monitor Dolby mixes correctly, as well as play your own and other studios’ printing masters and optical soundtracks. To this end you will need to install a Dolby cinema processor type CP650S1. The CP650S will provide analogue and digital optical replay, Surround-EX decoding, matrix decoding, full equalisation2 for loudspeaker calibration on all 7 channels, surround delay and master monitor level control. The CP650S uses AES/EBU digital inputs and analogue, digital or analogue cross-over outputs.

6.2. Optical replay of both the analogue and digital optical track is required for foreign version and original feature mixing to allow the studio to match the original recording, or to check the quality of an “Answer Print”. This will require a solar cell and bracket assembly for analogue replay, as well as a Cat. No. 702 or an approved Dolby Digital reader to be added to the projector or sound follower. The sound follower or projector must be able to run in synch with the studio recorders.

6.3. The screen and surround speakers and amplifiers must be capable of providing a frequency response to ISO2969 and, with the requirements of Dolby Digital in mind, must be able to provide an SPL of 105dBC for peak levels, after acoustic calibration, without distortion. Theatre type speakers (pressure drivers with suitable horns) will be required in medium to large rooms and these should have electronic crossovers. Appendix A gives further guidance. Bass management systems are not suitable.

The Dolby Studio Approval Calculator should be used to verify loudspeaker and amplifier performance capabilities. Suitable test material is available to check monitor headroom capability (“Jiffy” test film tone sweep test and a pulsed short duration 0dBfs pink noise test). Please note that Dolby level pink noise, 85dBC, equates to around -14dBfs.

6.4. The screen speakers must be at a height to give good coverage in the mixing and listening area. When projecting a 2.35:1 picture the left and right speakers will be inside the edge of the picture area and provide a 45° angle ± 5° with the mixing position. If masking is used this must be of the acoustically transparent type. We recommend that the mixing position be placed 2/3 back from the screen and require that the screen is at least 5 meters from the mixer. The studio area will be greater than 45 meters square and room volume will be greater than 150 cubic meters. We will allow some small deviation to these requirements if, in our opinion, the proportions of the room and equipment layout are spoilt in order to comply. Room ratios will be within the shaded area shown in Figure 1 below and ideally close to the straight line.

6.5. The acoustics of the mixing room must conform to the acoustic characteristics shown in Figure 2. The reverberation time should ideally diminish and show no reversals with increasing frequency.

6.6. Ambient noise levels must not exceed NC-25 as measured according to ISO 9568 Background acoustic noise levels in theatres, review rooms and dubbing rooms.

6.7. Two track only “Printing Masters” must be supplied SR encoded for transfer to optical sound negative on RDAT, Hi-8 (DTRS) or as .wav files. Dolby Digital “Printing Masters” (6 track and 2 track) will be recorded on a Dolby Digital Master MOD (Magneto Optical Disk) within the Dolby Digital Encoder for transfer to optical negative. They must also be recorded to .wav files or Hi-8 (DTRS) tape. Some customers may still request them on 35mm magnetic film with SR noise reduction.

6.8. Mixing consoles must have a minimum of 32 channels providing full processing such as gain, EQ, dynamics and pan. The console must provide a minimum of 24 professional grade faders at least two panoramic controls to move sounds between at least four channels and preferably six. There must be a minimum of 8 group outputs. If the studio intends to mix big budget original productions the above will need to be significantly increased.

6.9. The monitor section of the console must provide PEC/DIR (direct/replay) switching for 8 signal paths and a 16×8 summing monitor matrix to provide correct monitor routing during pre-mixing. It must allow individual solos and mutes of source and monitor channels. If the studio intends to mix big budget original productions, the number of PEC/DIR switches and matrix inputs will need to be significantly increased. Virtual (internal) as well as external solutions are acceptable as long as the user interface is dedicated to this function.

6.10. The DMU and MME encoders have AES/EBU digital inputs. A Dolby or third- party ADAC may be used for interfacing the encoder to analogue consoles, but in order to enable full and correct functionality of the encoder, any third-party

ADAC must comprise:

• 8 channels of analogue to digital and digital to analogue conversion.
• A conversion from the studios analogue level to -20dBfs. Normally this
would be 0dBU or +4dBU equating to -20dBfs.
• Headroom of 20dB above the analogue reference level.

Converters not meeting the above specifications will not be accepted. If in doubt please advise us the make and model number intended.

A suitable safety limiter on the input to prevent hard clipping at levels over 20dB above reference is not a requirement but is a valuable addition to the specification.

6.11. Level standardisation at –20 dB below MSB or clip in the console main outputs and recorders is essential. You may wish to check with the manufacturer that digital and line levels conform to accepted standards i.e. +4dBu or 0dBu line level for –20 dBFS internal console level and that the meters read –20 dB.

6.12. For synchronisation, the Dolby encoders require time code and video reference signals. The DMU can also work with biphase (a 240 or 48 pulse per frame bi-phase signal for a 24 frame per second rate). The studio must ensure they can supply the appropriate synchronisation signals prior to digital mastering.

6.13. Video projection must provide an image that when projecting a film made in an aspect ratio of 1.85:1 (flat) or 2.35:1 (scope), covers the width of the screen to at least the outer edge of the left and right screen speakers. Reflected light from screen (measured at mixing position) must be at least 12fL, and the pixel resolution of the projector must be a minimum of 1920 x 1080. Processing delay must be known and compensated for by a suitable timecode offset to the video replay device. If in doubt, please provide us with specifications and we will determine suitability.