XDR = eXtended Dynamic Range A quality standard set forth by EMI for use on their pre-recorded Compact Cassette's, in practice there was nothing novel or interesting about the system it simply meant that modulated tones were used at the beginning and end of each side allegedly to monitor quality but in actuality these were command codes for the automatic high speed duplicating and casing machinery and EMI put the "quality assurance" info on their tapes since they were worried that customers would write in to complain about the audio range control codes.
Apart from that the only difference between XDR and earlier tapes from EMI was that all tapes used the Dolby HX Pro system, the tape stock used was still fairly cheap ferric etc..
XRCD = Extended Resolution CD A set of standards put forward by JVC that specifies how a CD should be mastered to a great detail. It's important to note that this is a standard, not a technology like HDCD and that JVC's classification of it as a "high resolution format" is misleading at best, but as a sort of a quality assurance it's a "good thing™". Homepage:http://www.xrcd.com
100v = 100 Volts Sometimes called "constant voltage systems", this is a standard that allows multi speaker systems to be inexpensively implemented. In a standard audio system you can only connect loudspeakers to an amplifier in series and then you will only have a limited number of speakers due to impedance issues and a limited length of cables due to both impedance and signal loss issues.
In a 100v system an amplifiers output is connected to a step-up transformer that jacks the voltage up to a max of 100v, a step down transformer is then placed in each loudspeaker or loudspeaker array. This allows you to connect as many speakers in parallel as you want and cuts down cost considerably since you will only have to use one amplifier for each sound channel and one cabling system as well.
This has some added benefits, a typical step down transformer will have multiple power and impedance outputs, allowing you to choose how loud the speaker will sound and use speakers with different load characteristics. These 100v systems are mostly used in sound installation system rather than PA systems, commercial audio installations are almost exclusively 100v.
There are similar systems of a lesser voltage but that work in exactly the same fashion, including 50v and 75v, these are more common in Eastern Europe than in the rest of the world but in the west 25v and 70v systems are also known but are used more in local distribution than in whole buidings due to higher signal losses.
1394 A high speed serial digital communication interface invented by Apple Computer Corp. and often seen on digital consumer equipment such as video cameras and personal computers, usually goes by the name of Firewire (Apple term) or iLink (Sony term). Has been adopted as a carrier for high resolution and or multitrack digital audio in the SACD interconnect standard and is also used by some manufacturers as a property digital interlink especially for home A/V applications were higher data rates are needed than established standards will allow.
For more info visit the Document cache at the TI site or the 1394 Industry Association homepage. Yamaha also had an interesting 1394 based protocol called Mlan (Music Lan) that allows for the transport of multiple tracks of audio data along with other music data such as MIDI, this is confined to PCM audio only, no DSD, although high PCM bit rates are supported, sadly however it appears they have dropped support for the protocol recently, but they still have some information stored here.
30 Degree Principle An phrase used by Nobuyuki Idei of Sony to explain why the convergence between computers and AV devices has not happened. Basically the idea is that while you are sitting in front of a computer you lean forward 30° and focus while when you sit in front of a TV you lean back 30° and relax. This explains why it is tolerable to wait 10 seconds for a result from a computer when a 1,5 second delay while changing a channel on a TV is considered completely intolerable.
48 States Mainland USA, this phrase or the variant "lower 48 states" is used to indicate the states and commonwealths that belong to the USA and reside on the North American mainland. That excludes islands such as Hawaii, parts of the mainland that are not directly connected to the lower 48 ones such as Alaska and dependencies or "protectorates" such as Puerto Rico. This is important for trade inside the USA since postage and shipping cost are often harmonised inside the 48 states but the rest is treated as foreign.