Digital audio technology is fast moving, constantly innovating, this introduction brings you up to speed in no time.


Audio Representation

Digital Audio signals are represented by three different parameters, each of these has an effect on audio quality, for best quality match the encoder with the source, example: compressing an Audio CD, encode to 2 Channel, 16 bit, 44.1 KHz.



Audio CDs contain 2 channels of audio, that is 2 independent audio signals. The idea being your Hi-Fi has two speakers, the listener sits in the middle facing the speakers, their two ears detect differences from each speaker (created during CD mastering), this gives depth to the audio reproduction, called stereo separation, as well placing the vocalist in the centre of the two speakers.

Movies benefit more than music from extra speakers, effects some times need to appear from behind, it is easier to effect this when there are actual speakers at the rear. DVDs have 5.1 sound: 5 speakers and .1 is the low frequency sub-woofer.

Why is music not 5.1? traditionally if a concert was attended, all sound would appear to come from the front, nothing from behind, where as a car chase in a film the police sirens would be behind. That is not to say music cannot improve with more speakers, certain tracks might try to place the listener in the middle of audio, if I had the choice of 2 very good speaker or 5 average ones, I would choose the two good for music.

Channel Count Common Name
1 Mono
2 Stereo
4 Quadrophonic
6 5.1
8 7.1



Frequency (Sample Rate, or Samples Per Second)

Sound is made up from pressure waves. A single constant wave has its frequency measured in Hz (oscillations per second). Humans can hear from a lowest frequency of 10's of Hz, up-to higher frequencies just below 20,000 Hz, or 20 KHz.

When talking about digital audio, frequency has a different meaning, it is the rate each sound sample is recorded. Imagine you were told the temperature out side once a day, your friend was told the temperature four times a day, who would have the more accurate picture? your friend. The higher the frequency, the more accurate a representation, up to a point...human hearing can not hear above 20 KHz, so reproducing 50,000 KHz would be a waste of space (each sample takes up space). Nyquist's theorem states: that to reproduce a 22 KHz sound signal, it must sampled (recorded) at more than 2x the required frequency, a sample rate of 44.1 KHz can reproduce a 22 KHz signal.

It just so happens that audio CDs have a sample rate of 44.1 KHz, so why is DVD audio 96 KHz, or 192 KHz? is it a marketing ploy? yes and no. Yes it is a ploy in that more appears to be better, it has already been said that an audio CD can reproduce a sound that has a higher frequency than people can hear. No, as it is easier (cheaper) to create a piece of audio equipment that plays back a 18 KHz signal without distortion, when fed a 192 KHz signal rather than a 44.1 KHz signal. High-end gear, would not have much distortion, so there is no point in 96, or 192 KHz audio, just the cheaper consumer gear which improves.


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  • Bit Depth (and Amplitude)

    Consider these two audio sine waves:


    B has a higher amplitude (2x) than A, it is louder, but B is not twice as loud as A, perceived audio loudness works on a logarithmic scale. The human ear was designed this way, so that the quietest mouse can be heard whilst the loudest jet tolerated (there is many order of magnitudes difference between the two).

    Bit depth is the resolution audio samples can be stored with, consider these 3 images as representations of bit depth:

    8bit 16bit 24bit
    8 bit 16 bit 24 bit

    8 bit has the worst detail, it looks coarse, for audio it sounds coarse, but there is not too much difference between 16 bit and 24 bit, they are both reaching the limits of perception. Audio CDs are 16 bit, whereas DVDs are 24 bit, again is it a marketing ploy? yes and no, yes most people cannot hear the difference between the two, no as 16 bit audio CDs have been spoilt by the loudness race: that is CDs produced now are volume compressed, that is the quiet parts are pushed up louder, so that when played on the radio or TV the track sounds louder (a 1980's CD would sound quiet in comparison to one from 2000). The downside is that 16 bit CDs are no longer effectively 16 bit, the full audible range is not being used. 24 bit helps, but in the long run, the same fate (loudness war) might happen to 24 bit DVD-audio discs.

  • Compression

    When talking audio, compression can have two meanings: volume compression where the volume levels are 'compressed' to make the overall piece louder and audio compression, used to reduce the file size. We are discussing audio compression, of which there are two types:

    • Lossy the majority of compressed audio files are lossy, when encoding audio quality is sacrificed to achieve higher rates of compression. How much quality is lost depends on the encoder and settings used for compression, bit rate plays the biggest role in determining final quality, higher bit rate files have better quality than lower bit rate files. Bit rate is normally presented in Kbps (Kilo-bits-per-second). Bit rate can be fixed at the same value throughout the file, know as Constant Bit Rate, or CBR. Bit rate can constantly vary on demand, an audio track might have quiet parts, it stands to reason that for these quiet parts a lower bit rate could be used, whilst complex parts a higher bit rate could be used. When the bit rate is allowed to change it is called Variable Bit Rate, or VBR. Finally there is Average Bit Rate (ABR), basically it is VBR but with constraints, those constraints are to give the whole file an average set bit rate, so the final file size can be roughly known (with VBR it could be any size).Typically a lossy 3 minute audio track might be 3 MB in size, around 10 to 1 compression (at 160 Kbps), or 10% of it's uncompressed size. Common lossy encoders are: mp3, ogg vorbis, windows media audio (wma), advanced audio compression (AAC, typically stored in a .m4a container).
    • Lossless: audio which is compressed using lossless can be uncompressed exactly the same (bit for bit) as the source file, it is without loss. Lossless is slowly gaining ground on Lossy, the main advantage being once your CD collection is ripped into lossless that is it, no more re-ripping, unlike lossy where the need to re-rip might present its self if a newer encoder is released. Lossless can be converted to any other Lossless format without loss, lossless can be converted to any lossy format and has the same quality as though ripping from audio CD. The main reason Lossless is held back, is the final compression rates which are no where near as good as Lossy, a typical 3 minute audio track might be around 30 MB uncompressed, Lossless could compress down to 15 MB, around 2 to 1 compression, or 50% of it's uncompressed size.



    ysb-logo-cdtextCD-Text is an extension of the Red Book Compact Disc specifications standard for audio CDs. It allows for storage of additional information (e.g. album name, song name, and artist) on a standards-compliant audio CD. The information is stored either in the lead-in area of the CD, where there is roughly five kilobytes of space available, or in the Subchannels R to W on the disc, which can store about 31 megabytes. The latter areas are not used by strict Red Book CDs. The text is stored in a format usable by the Interactive Text Transmission System (ITTS). ITTS is also used by Digital Audio Broadcasting or the MiniDisc.

    The specification was released in September 1996 and backed by Sony. Support for CD-Text is common, but not universal. Utilities exist to automatically rip CD-Text data, and insert it into CDDB or freedb.

  • DTS

    ysb-logo-dtsDTS is a series of multichannel audio technologies owned by DTS, Inc. (formerly known as Digital Theater Systems, Inc.), an American company specializing in digital surround sound formats used for both commercial/theatrical and consumer grade applications. It was known as The Digital Experience until 1995.

    In 2008, the cinema division was divested to form DTS Digital Cinema. In 2009 DTS Digital Cinema was purchased by Beaufort International Group Plc. and became known as Datasat Digital Entertainment. Beginning in 2011, the DTS cinema branding has been dropped, in favor of the Datasat Digital Sound branding. The original DTS Inc. company continues to exist developing and licensing DTS products in the home consumer market. Datasat Digital Entertainment has also announced a range of very high-end consumer audio processing products.

    DTS audio codec On the consumer level, DTS is the oft-used shorthand for the DTS Coherent Acoustics codec, transportable through S/PDIF and part of the Laserdisc, DVD, and Blu-ray specifications. This system is the consumer version of the DTS standard, using a similar codec without needing separate DTS CD-ROM media.

    Both music and movie DVDs allow delivery of DTS audio signal, but DTS was not part of the original DVD specification, so early DVD players do not recognize DTS audio tracks at all. The DVD specification was revised to allow optional inclusion of DTS audio tracks. The DVD title must carry one or more primary audio tracks in AC-3 or LPCM format (in Europe, MPEG-1 Audio Layer II is also an allowed primary track format). The DTS audio track, if present, can be selected by the user. Subsequent DVD players now decode DTS natively or pass it through to an external decoder. Nearly all standalone receivers and many integrated DVD player/receivers can decode DTS.

    A small number of Laserdiscs carry DTS soundtracks. The NTSC Laserdisc format allows for either analog audio only or both analog and digital audio tracks. Laserdiscs encoded with DTS sound replace the LPCM digital audio track with the DTS soundtrack. This soundtrack is output via digital coaxial or optical audio outputs and requires an external decoder to process the bitstream.

    For PC playback, many software players support the decoding of DTS. The VideoLAN project has created a decoding module for DTS called libdca (formerly libdts), which is the first open source implementation of DTS.

    Sony's PlayStation 3 and Microsoft's Xbox 360 are capable of DTS decoding and output via TOSLINK or HDMI as LPCM. However, HDMI output on the Xbox 360 is only found on the "Elite" model and newer models available since mid-2007, with the release of the Falcon motherboard revision. Also, the Xbox 360 cannot decode DTS from DTS Audio CDs. PlayStation 3 consoles can bitstream DTS over HDMI. The newer "slim" models are able to bitstream DTS-HD MA as well.

    DTS variants

    In addition to the standard 5.1-channel DTS Surround codec, the company has several other technologies in its product range designed to compete with similar systems from Dolby Labs. Those which conceptually extend DTS (to add more channels and/or more accurate sound reproduction) are implemented as extensions to a core DTS Coherent Acoustics data stream. The core stream is compatible with DTS decoders which do not support the extension(s); the extension(s) provide the additional data required to implement the additional functionality.

    The primary new technologies are:


    ysb-dtsesDTS-ES (DTS Extended Surround) includes two variants, DTS-ES Matrix and DTS-ES Discrete 6.1, depending on how the sound was originally mastered and stored. Both variants are implemented in ways which are compatible with DTS decoders which do not include support for DTS-ES.

    DTS-ES Matrix provides 5.1 discrete channels, with a matrixed center-surround audio channel. DTS processors that are compatible with the ES codec look for and recognize "flags" built into the audio coding and "unfold" the rear-center sound from data that would otherwise be sent to rear surround speakers. DTS decoders which do not understand ES process the sound as if it were standard 5.1, and the matrixed audio for the center surround channel is output equally from the two surround speakers (very much as a sound intended to be in the centre of the sound field in a stereo recording is played equally by the left and right speakers). This is notated as DTS-ES 5.1.

    DTS-ES Discrete provides 6.1 discrete channels, with a discretely recorded (non-matrixed) center-surround channel; in home theater systems with a 7.1 configuration, the two rear-center speakers play in mono. To maintain compatibility with DTS decoders which do not support DTS-ES, the center-surround channel is also matrixed into the left and right surround channels, so that the rear center channel's sound is still present when played in 5.1 on a non-ES system; an ES decoder removes the matrixed audio from these two channels when playing back DTS-ES Discrete soundtracks. DTS-ES Discrete is sometimes notated as DTS-ES 6.1. Only a few DVD titles have been released with DTS-ES Discrete.

    In contrast, Dolby's competing EX codec, which also boasts a center rear channel, can only handle matrixed data and does not support a discrete sixth channel; it is most directly comparable to DTS-ES Matrix.


    The center-rear/surround channel is encoded and decoded in exactly the same way as the center-front. The center surround channel can be decoded using any surround sound processor by feeding the left and right surround signals to the processor inputs. Left-Center-Right surround is produced. This will work for a "center surround" reproduction, whether the source material is explicitly encoded, as in DTS-ES, or hidden as ambience in any 5.1 source, including DTS-ES 5.1 and Dolby 5.1.


    DTS Neo:6

    ysb-dtsesneo6DTS Neo:6, like Dolby's Pro Logic IIx system, can take stereo content and convert the sound into 5.1 or 6.1 channel format, but in a 7.1 configuration, the two rear-center speakers play in mono. Unlike Dolby Pro Logic II's broadband logic steering, Neo:6 is a multi-band decoder, meaning that the decoder can enhance more than one predominant signal at a time — provided each predominant signal lies in a different frequency band than the others. The number of bands steered varies in each Neo:6 implementation, with the first decoders steering in 12 separate bands and later units steering up to 19.


    DTS Neo:X

    ysb-dtsneoxDTS Neo:X can take stereo, 5.1, 6.1, or 7.1 source material and output up to 11.1 channels including front height and width channels. Unlike Dolby's Pro Logic IIz's system, which only adds front height channels to the 7.1 configuration, Neo:X supports both front height and front wide channels. DTS Neo:X also supports 11.1 encoding through matrixing of front height and front wide channel information into the front and surround channels, respectively, of a 5.1 or 7.1 audio mix.


    DTS 96/24

    ysb-dts96DTS 96/24 allows the delivery of 5.1 channels of 24-bit, 96 kHz audio and high quality video on the DVD-Video format. Prior to the development of DTS 96/24, it was only possible to deliver two channels of 24-bit, 96 kHz audio on DVD Video. DTS 96/24 can also be placed in the video zone on DVD-Audio discs, making these discs playable on all DTS-compatible DVD players. DTS 96/24 is implemented as a core DTS stream plus an extension containing the deltas to enable 96/24 sound reproduction.


    DTS-HD High Resolution Audio

    ysb-dtshraDTS-HD High Resolution Audio, along with DTS-HD Master Audio, comprise the DTS-HD extension to the original DTS audio format. It delivers up to 7.1 channels of sound at a 96 kHz sampling frequency and 24-bit depth resolution. DTS-HD High Resolution Audio is selected as an optional surround sound format for Blu-ray Disc and HD DVD, with constant bit rates up to 6.0 Mbit/s and 3.0 Mbit/s, respectively. It is intended to be an alternative for DTS-HD Master Audio where disc space may not allow it. DTS-HD High Resolution Audio is implemented as a core DTS stream plus an extension containing the two additional channels plus deltas to enable 96/24 sound reproduction.


    DTS-HD Master Audio

    ysb-dtshdmaDTS-HD Master Audio, previously known as DTS++ is the second of two DTS-HD audio formats. It supports a virtually unlimited number of surround sound channels, can downmix to 5.1 and two-channel, and can deliver audio quality at bit rates extending from DTS Digital Surround up to lossless (24-bit, 192 kHz).

    DTS-HD Master Audio is selected as an optional surround sound format for Blu-ray and HD DVD, where it has been limited to a maximum of 8 discrete channels. DTS-HD MA supports variable bit rates up to 24.5 Mbit/s on a Blu-ray Disc and up to 18.0 Mbit/s for HD DVD, with up to 6 channels encoded at up to 192 kHz or 8 channels encoded at 96 kHz/24 bit. If more than two channels are used, a "channel remapping" function allows for remixing the soundtrack to compensate for a different channel layout in the playback system compared to the original mix.

    All Blu-ray and HD DVD players can decode the DTS "core" resolution soundtrack at 1.5 Mbit/s, however, as DTS-HD Master Audio is also implemented as a standard DTS core plus extensions. DTS-HD Master Audio and Dolby TrueHD are the only technologies that deliver compressed lossless surround sound for these new disc formats, ensuring the highest quality audio performance available in the new standards. (DTS Coherent Acoustics' coding system has been selected as mandatory audio technology for both the Blu-ray Disc [BD] and HD DVD).


    DTS Connect

    ysb-dtsconnectDTS Connect is a blanket name for a two-part system used on the computer platform only, in order to convert PC audio into the DTS format, transported via a single S/PDIF cable.[8] The two components of the system are DTS Interactive and DTS Neo:PC. It is found on various CMedia soundcards and onboard audio with Realtek ALC883DTS/ALC889A/ALC888DD-GR/ALC892-DTS-CG and SoundMAX AD1988 chips, as well as several cards based on the X-Fi chipset, such as the SoundBlaster Titanium series and Auzentech's X-Fi Forte, X-Fi Prelude, X-Fi Home Theater HD and X-Fi Bravura cards.

    • DTS Interactive: This is a real-time DTS stream encoder. On the PC, it takes multichannel audio and converts it into a 1.5 Mbit/s DTS stream for output. Because it uses the original DTS codec to transmit audio, fidelity is limited to 5.1 channel at 48 kHz, 24bit. More than 5.1 channels, a higher sampling frequency or data rate are not supported, due to the lack of support for DTS variants such as DTS 96/24. It can also be found on some standalone devices (e.g., Surround Encoder). Nearly a dozen titles on the PlayStation 2 feature the "DTS Interactive" real-time stream encoder, such as Grand Theft Auto: Vice City and Terminator 3: Rise of the Machines.
    • DTS Neo:PC: This is a technology based on the DTS Neo:6 matrix surround technology, which transforms any stereo content (MP3, WMA, CD Audio, or games) into a simulated 7.1-channel surround sound experience. The 7.1-channel surround sound is output as a DTS stream for output via a S/PDIF cable port.

  • DOLBY Digital

    ysb-dolbyDolby Digital is the name for audio compression technologies developed by Dolby Laboratories. It was originally named Dolby Stereo Digital until 1994. Except for Dolby TrueHD, the audio compression is lossy. The first use of Dolby Digital was to provide digital sound in cinemas from 35mm film prints. It is now also used for other applications such as HDTV broadcast, DVDs, Blu-ray Discs and game consoles.



    Dolby Digital

    ysb-dolbydigitalDolby Digital is the common version containing up to six discrete channels of sound. The most elaborate mode in common use involves five channels for normal-range speakers (20 Hz – 20,000 Hz) (right, center, left, right surround, 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. The LaserDisc version of Clear and Present Danger featured the first home theater Dolby Digital mix in 1995.

    This format has different names:

    • 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. Adaptive Transform Acoustic Coding 3 is a separate format developed by Sony.])
    • ATSC A/52 (name of the standard)


    Dolby Digital EX

    ysb-ddexDolby Digital EX is similar in practice to Dolby's earlier Pro-Logic format, which utilized matrix technology to add a center surround 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

    ysb-ddsuroundexThe cinema version of Dolby Digital EX is called Dolby Digital Surround EX and works similarly. It 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 with Surround EX decoding and added 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

    ysb-ddexliveDolby Digital Live (DDL) is a real-time 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 640 kbit/s and transports it via a single S/PDIF cable. A similar technology known as DTS Connect is available from competitor DTS. An 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 sound because S/PDIF over RCA, BNC, and TOSLINK can only support two-channel PCM, Dolby Digital multichannel audio, and DTS multichannel audio. HDMI was later introduced, and it can carry uncompressed multichannel PCM, lossless compressed multichannel audio, and lossy compressed digital audio. However, Dolby Digital Live is still useful with HDMI to allow transport of multichannel audio over HDMI to devices that are unable to handle uncompressed multichannel PCM.

    Dolby Digital Live is available in sound cards using various manufacturers' audio chipsets. The SoundStorm, used for the Xbox game console and certain nForce2 motherboards, used an early form of this technology. DDL is available on motherboards with codecs such as Realtek's ALC882D, ALC888DD and ALC888H. Other examples include some C-Media PCI sound cards and Creative Labs' X-Fi sound cards whose drivers have enabled support for DDL.

    NVIDIA later decided to drop DDL support in their motherboards due to the cost of involved royalties, leaving an empty space in this regard in the sound cards market. Then in June 2005 came Auzentech, which with its X-Mystique PCI card, provided the first consumer sound card with Dolby Digital Live support.

    Initially no Creative X-Fi based sound cards supported DDL (2005~2007) but a collaboration of Creative and Auzentech resulted in the development of the Auzentech Prelude, the first X-Fi card to support DDL. Originally planned to extend DDL support to all X-Fi based sound cards (except the 'Xtreme Audio' line which is incapable of DDL hardware implementation), the plan was dropped because Dolby licensing would have required a royalty payment for all X-Fi cards and, problematically, those already sold. In 2008, Creative released the X-Fi Titanium series of sound cards which fully supports Dolby Digital Live while leaving all PCI versions of Creative X-Fi still lacking support for DDL.

    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 incapable of DDL in hardware). X-Fi's case differs.

    While they forgot about the plan, programmer Daniel Kawakami made a hot issue by applying Auzentech Prelude DDL module back to Creative X-Fi cards by disguising the hardware identity as Auzentech Prelude.

    Creative Labs alleged Kawakami violated their intellectual property and demanded he cease distributing his modified drivers.

    Eventually Creative struck an agreement with Dolby Laboratories regarding the Dolby license royalty by arranging that the licensing cost be folded into the purchase price of the Creative X-Fi PCI cards rather than as a royalty paid by Creative themselves.[16] Based on the agreement, in September 2008 Creative began selling the Dolby Digital Live packs enabling Dolby Digital Live on Creative's X-Fi PCI series of sound cards. It can be purchased and downloaded from Creative. Subsequently Creative added their DTS Connect pack to the DDL pack at no added cost.


    Dolby Digital Plus

    ysb-ddplusE-AC-3 (Dolby Digital Plus) is an enhanced coding system based on the AC-3 codec. It offers increased bitrates (up to 6.144 Mbit/s), support for more audio channels (up to 13.1), and improved coding techniques (only at low data rates) to reduce compression artifacts, enabling lower data rates than those supported by AC-3 (e.g. 5.1-channel audio at 256 kbit/s). It is not backward compatible with existing AC-3 hardware, though E-AC-3 decoders generally are capable of transcoding to AC-3 for equipment connected via S/PDIF. E-AC-3 decoders can also decode AC-3 bitstreams. Only the discontinued HD DVD system directly supported E-AC-3, though Blu-ray Disc offers E-AC-3 as an option to graft added channels onto an otherwise 5.1 AC-3 stream, as well as for delivery of secondary audio content (e.g. director's commentary) that is intended to be mixed with the primary audio soundtrack in the Blu-ray Disc player.


    Dolby TrueHD

    ysb-ddtruehdDolby TrueHD, developed by Dolby Laboratories, is an advanced lossless audio codec based on Meridian Lossless Packing. Support for the codec was mandatory for HD DVD and is optional for Blu-ray Disc hardware. Dolby TrueHD supports 24-bit, 96 kHz audio channels at up to 18 Mbit/s over 14 channels (HD DVD and Blu-ray Disc standards currently limit the maximum number of audio channels to eight). It supports metadata, including dialog normalization and Dynamic Range Control.



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