Page
Update
3/27/05
For the Surround Sound Theater
5.1
Five channels consisting of two front Stereo speakers plus two rear stereo speakers plus a front center speaker in addition the .1 refers to a separate output for externally powered sub-base woofers (see LFE). Technally, the term indicated that each of the five channels are derived from separate digital information. However, consumer marketing has used the term to discribe the product when the end result is the same but in actuallality the center channel is derived from the left and right front channels on the analog level by using matrix processing.
6.1
Same as 5.1 but also provides additional center-rear speaker(s). It can also facilitate an additional standard stereo pair used for remote speakers. The 6.1 has become accepted by some to apply not only to discrite digital data for each of the six channels but also the matrix technique of deriving both the front and rear channel information from their adjacent left and right analog signals.
"7.1"
Not yet a true surround sound format. Rather it refers to home theater equipment manufacturers' proprietary implementation of two back surround channels. Usually, the audio signal fed to the two back surround channels are identical, but some manufacturers may choose to mix some information from the left and right surrounds. Again, these are proprietary implementations that vary across manufacturers and are not industry standards
AAC: (see MPEG-4)
AC-3
A compression algorithum for audio used by Dolby Digital. The two terms, AC-3 and Dolby Digital, are often used interchangeably.
A newer addition to old laserdiscs that enables Dolby Digital output but because it is modulated into the space formerly occupied by the right channel analog signal. To extract the digital sound it is output to a home-theator turner that has a dedicated “AC-3 RF” input so it can. The tuner then de-modulates the signal befor handing it over to the Dolby Digital processor.
A/V Amps and Tuners:
Before buying a tuner or an or an A/V Amplifier, determine what Video signal types it can switch with the audio. See Nick Notes Video Standards. No TV can compete with a dedicated audio system, so even if your set has lots of watts and simulated surround sound, you should consider a home-theater audio system for maximum impact. If you have such a system, the TV's sound becomes a moot point. Note: some A/V Amps can have software or fermware upgrades to accommodate the changing audio formats as they evolve (see PCM).
Audio Compression
Various techniques, (from analog non-linear op-amps to digital algorithms) applied to stored audio for squeezing the most audio quality into and out-of the least available recording space.
Audio CD
The original commercially produced stereo CD is a 16-bit medium with a max. sound reproduction of 44.1kHz.sampling at 44.1 kHz.
Audio DVD
Uses a file format for storage of Audio files utilizing the features developed by Digital Theator Systems (see DTS below) and providing higher audio quality than a standard audio CD.
In 5.1 digital surround sound, the .1 refers to the LFE or Low Frequency Effects channel. It is also refered to as the subwoofer channel and the “boom track”.
To ensure compatability with formats not containing LFE data, the low frequency of the other five channels are also routed to this dedicated output. Low frequency is not particularly directional and not as vulnerable to phase distortion so using a single dedicated speaker with its own amplifier is a cost efficient method of producing good base sound. A self containd sub-base speaker with its own power amp can make a cheap 50watt A/V Tuner/Amplifier sound fairly good. Most high end systems also use the dedicated single base approach.
Digital Audio Compression Algorithms
Techniques used to reduce the amount of data required for reproducing audio successfully.
DSP Digital Signal Processor (or Processing)
Adds additional channel effects to non-dolby or non-DTS digital media; DSPs can synthesize a limited 5.1 surround from two channel stereo digital media or add additional chanels to
“5.1” to deliver a simulated 6.1 etc.
DTS
Developed by Digital Theater Systems for film soundtracks. Requires more storage space on a DVD than does Dolby Digital but provides higher audio quality equivilent to the quality of any original studio mastering.
DTS 4.0 is four discrete audio signals for the center, left, and right channels, plus a mono audio signal that is common for the surround channels.
DTS 4.1 is like DTS 4.0, but adds the ".1" low frequency effects.
DTS 6.1 (Two types one discrite the other a matrix; see DTS-ES)
DTS 96/24: 96 kHz capability due to a 24-bit sampling medium. This format may be available on a DVD and is backwards compatable with basic stereo players but for the full benefit requires a player with five audio chanels (5.1 hardware).
Devices carrying this logo (DTS Neo:6 ) and all DTS-ES-equipped receivers are able to provide decoding for all the following formats: DTS 6.1, DTS 5.1, two- to 6.1-channel matrix decoding, (Dolby), and all two-channel content. Devices with this logo also have the hardware to output on 5 or 6 discrete audio channels.
DTS-ES Matrix or DTS-EX is a 6.1-channel matrix extended surround sound format for movie theaters.
DTS-ES: True 6.1. This Extended Surroundsound utilizes extra data bits appended on the 5.1 format to provide a 6.1 with true discrite six channel sound. The format could enable future developments such as 10.1. Currently it is also called DTS-ES Discrete 6.1
(in contrast to its matrix counterpart, DTS-ES Matrix). Visit www.dtsonline.com
THX: (see Dolby below)
Dolby Digital (formerly known as Dolby AC-3, where AC-3 is short for audio coding 3)
Developed by Dolby Laboratories originally for film soundtracks. It is highly compressed and is especially useful when space or bandwidth is restricted. It supports multiple sound formats from monorail to a 6.1.
Analog Matrix Decoding enables a center channel to be derived from two (left and right) analog channels or a rear channel to be derived from the surround left and right.
Dolby Digital 5.1: Two front Stereo speakers plus two rear stereo speakers plus a front center speaker in addition to a separate output for externally powered sub-base woofers.
Dolby Digital 6.1: Same as 5.1 but includes an additional standard stereo pair (and also sometimes used for remote speakers). Dolby Digital Surround EX is the format that enables the center rear channel in 6.1 to be derived from the left and right surround (rear) channels. The rear center channel is derived from the phase relationships of the rear left and right channels. Basicly, THX Surround EX is the same as Dolby Digital EX is the same as Dolby Digital 6.1.
The primary advantage of DTS is that it offers higher data rates and provides discrete digital audio channels, thus it can outperform Dolby Digital in sound quality. The down side is that a DTS soundtrack uses more of the disc's data capacity due to its higher data rate. Curently, DTS is not a standard soundtrack format for DVD-Video makes, it is an optional 5.1-channel surround format that is, so far, there are far more DVD-Video titles with Dolby Digital soundtracks than there are those with the DTS surround sound format.
The DTS interconnects via PCM jacks (see PCM jack).
MP3: Digitally Compressed audio that supports up to 48kHz sampling (at the sacrifice of file size). Roughly, one minute of audio consumes one megabyte of storage.
MPEG-4 Audio (or MP4 or DivX): An Audio Video compression technology that includes Advanced Audio Coding (AAC). Rumored to replace MP3 because it compresses smaller yet can do 96kHz, more than twice the sound quality of a standard audio CD. AAC is more powerful because it adjusts compression with a variable bit rate (VBR) depending on the complexity of the sound. It actually requires less processing power than MP3, and is so versatile it supports up to 48 separate full-frequency audio channels!
PCM (Pulse Code Modulation)
Digital audio and some video is incoded using this format. Two variables effect the quality of the decoded audio: sample rate and bit rate. The sample rate is how many samples per sceond are in the digital media (time slices) and the bit rate is how many bits are used for each word used to discribe a single time slice. More is better. 8 bit words are at the low end and for audio and the original audio CD uses a 16 bit word. The sample rate is also very important since the closer each time slice is to each other the more accurately the sound can be reproduced. Half the sample rate is the max frequency that can be captured. Three new improvements to the original 16bit CD are now on the market:
HDCD (High Definition Compatible
Digital): this creates a 20-bit resolution out of the 16-bit format.
DVD-Audio: Music on a DVD with bonus graphical information
or music videos.
SACD (Super Audio CD): Another high-end
audio format developed by Sony and Philips.
PCM jack: The dedicated audio jack used for DTS (Digital Theater Systems) [contender to the dolby formats]. Upper-end CD and DVD players have this jack which must be connected with a Tuner that also supports the PCM type connector for DTS.
(Visit www.pacificcable.com for more info.)
VBR: (see MPEG-4)
Coherent Acoustics: a digital audio compression algorithm designed for both professional and consumer applications of DTS. The algorithm is highly flexible, operating over multiple channels of audio, at sampling rates up to 192 kHz, with up to 24-bit resolution.
Linear PCM Coding: The first Compression Algorithm used for audio CDs.
Historically, digital audio players, such as CD and DAT players, have used linear PCM coding for storing. Its becomes less efficient as more audo channels are implimented.
S/PDIF (Sony/Philips Digital
Interface) is a standard digital audio transfer file format. It
allows the transfer of audio from one file to another without the
conversion to and from an analog format, which could degrade the
signal quality. The most common connector used with an S/PDIF
interface is the RCA connector, the same one used for consumer audio
products. An optical connector is also sometimes used and provides
extra resiliance against induced noise, surges and lightning. The
coax version is coupled at each end to a isolation transformer which
also protects the equipmemt. Comcast HD Cable service provides the
Motorola DCT5100 cable box that sports both coaxal (RCA) and optical
SPDIF.
THX (THX Home): a set of technical specifications, circuits, and standards developed by Lucasfilm, Ltd. to make sure that you hear movie soundtracks in your home just as the director and sound engineers intended them to be heard. Lucasfilm, Ltd. (yes, the "Star Wars" people!) licenses this technology only to manufacturers whose products adhere to its strict requirements. Home THX is not a Dolby competitor. THX technologies begin to work only after Dolby delivers a multi-channel signal for additional processing.
WATTS: Power Formulas Of A Sinusoidal Wave Form (pure flute sound):
RMS = 0.707 x Peak or 1.11 x Average
Peak = 1.414 x RMS or 1.57 x Average
Average = 0.9 x RMS or 0.637 x Peak
Fun Facts: Fundimentally a flute produces a sinusoidal sound wave. Read insturments almost produce a square wave. If the sound wave had peaks and vallys that were equal and instantinious in direction change then RMS = Peak = Ave; however air has mass so it cannot change in direction instantaniously; even electronically synthasizing a pure square wave will not produce one in the air. A loud audible click may also come close to producing a square wave but it’s duration is so small that its power is barely measurable. RMS (Root Mean Square) Power is a measurement of the actual energy. Marketing experts like the big number peak power gives, but this is a leagal way to lie.
Funky power measurements include “continous” (continuous power x 1.1 = peak power = 1.414 x RMS)
Continuous power is measured with pink noise. See:
http://www.epanorama.net/documents/audio/amplifier_power.html
Good References:
SurroundSound Resource: http://timefordvd.com/tutorial/SurroundSound.shtml
LFE Resource: http://www.hometheaterhifi.com/volume_7_2/feature-article-misunderstood-lfe-channel-april-2000.html
DVI Resource: http://www.datapro.net/techinfo/dvi_info.html