MP3 the MP3 Audio Format Lossy Data Compression. Audio Quality

Voice Data Voice data is something which is comprised of different wavelengths of sound. A simple exam can be found in an E.C.G Report of Heart. It has different wavelengths showing the Heartbeat. If you observe you will find that these wavelengths are of different height, which is basically indicating the Pitch of Sound Wave. Video Data Video data is a compilation of some Pixel or Vector based Images. A simple digital camera has an option of Multi Shot Mode. What happens in this mode is that a Picture is taken 10 to 15 times in a Sec. These images are then converted into a video. 1 Picture in this compilation will serve as 1 Frame. Now for a standard, Human Eye is capable of considering 30 Frames per second as a video. that means if 30 pictures are moved accross in front of human eye within a Second, it will turn into a video. A Simple example is an OLD Cinema House. In old days pictures, were used to entertain people in Cinema. Those pictures were moved across a projector with a speed of 30 FPS. Audio MP3 The MP3 audio format lossy data compression. Audio quality improves with increasing bitrate. 32 kbit/s - generally acceptable only for speech 96 kbit/s - generally used for speech or low-quality streaming 128 or 160 kbit/s – mid-range bitrate quality 192 kbit/s - a commonly used high-quality bitrate 320 kbit/s - highest level supported by MP3 standard Other audio 800 bit/s – minimum necessary for recognizable speech, using the special-purpose FS- 1015 speech codecs. 1400 bit/s – lowest bitrate open-source speech codec Codec2.[14] 2.15 kbit/s – minimum bitrate available through the open-source Speex codec. 8 kbit/s – telephone quality using speech codecs. 32-500 kbit/s – lossy audio as used in Ogg Vorbis. 256 kbit/s – Digital Audio Broadcasting (DAB.) MP2 bit rate required to achieve a high quality signal.[15] 400 kbit/s–1,411 kbit/s – lossless audio as used in formats such as Free Lossless Audio Codec, WavPack, or Monkey's Audio to compress CD audio. 1,411.2 kbit/s – Linear PCM sound format of CD-DA. 5,644.8 kbit/s - DSD, which is a trademarked implementation of PDM sound format used on Super Audio CD.[16] 6.144 Mbit/s - E-AC-3 (Dolby Digital Plus), which is an enhanced coding system based on the AC-3 codec. 18 Mbit/s - advanced lossless audio codec based on Meridian Lossless Packing. Video 16 kbit/s – videophone quality (minimum necessary for a consumer-acceptable "talking head" picture using various video compression schemes) 128–384 kbit/s – business-oriented videoconferencing quality using video compression 1.5 Mbit/s max – VCD quality (using MPEG1 compression)[17] 3.5 Mbit/s typ — Standard-definition television quality (with bit-rate reduction from MPEG-2 compression) 9.8 Mbit/s max – DVD (using MPEG2 compression)[18] 8 to 15 Mbit/s typ – HDTV quality (with bit-rate reduction from MPEG-4 AVC compression) 19 Mbit/s approximate — HDV 720p (using MPEG2 compression)[19] 24 Mbit/s max — AVCHD (using MPEG4 AVC compression)[20] 25 Mbit/s approximate — HDV 1080i (using MPEG2 compression)[19] 29.4 Mbit/s max – HD DVD 40 Mbit/s max – Blu-ray Disc (using MPEG2, AVC or VC-1 compression)[21] Good question! In US residential wiring, you have 3 wires feeding your home off the transformer: two hots and neutral. The transformer is a 240V center tapped transformer. The neutral is the center tap. Well, that's all fine and good, but your probably asking "what does that mean?" right about now. Well, since the transformer is 240V, you have 240V in between the two hots. The center tap divides the transformer winding in the middle. So between either hot and neutral you get 120V. Neutral is kind of a return wire for 120V circuits. (I say "kind of" because this is AC, current is flowing in both directons.) Well, why is it called neutral, then? At your main service panel a fourth wire comes into play: ground. Ground is simply a heavy safety wire that goes to a 8ft long copper rod driven into the ground. This ground wire is connected to all metal surfaces you touch (panels, screws, metal junction boxes, metal cases on appliances, etc.) In the main panel (and only the main panel) neutral is bonded to ground. So, while neutral is not ground, when everything is correct it should be "neutral," i.e. it has no potential on it. 120V safety issues You cannot assume neutral is grounded or safe to touch, however. By the very nature of wire, if there is a current in a wire there is a potential across it. This potential is usually very small, but is still there. The bigger problem is if the neutral connection becomes very resistive or open. Then the neutral will be live as it cannot "return" the energy to the transformer. (Again, not a totally correct analogy, but it gets the point across.) This is why you shouldn't just bond ground to neutral when you don't have a ground wire at a fixture. When a hot wire goes open, fixtures simply fail to operate. When a neutral goes open, the fixture and the neutral between the fixture and the break go live. The fixture will not work, however, giving people a false sence of security. (No the light is not on, yes it can knock you on your butt.) This is why you want to keep your neutrals in good shape. Neutral Balancing With the neutral you have two hot wires both capable of producing 120V to neutral. Because the hots have 240V across them (and not 0), one hot goes positive while the other hot goes negative. So, let's say you take two loads with a resistance of 60 ohms. You hook the neutrals of the loads up to neutral, one load to one hot, and the other load to the other hot. How much energy flows through the neutral conductor? 0W. This is because the load is "balanced." The amount of energy flowing through load one is equal to the energy flowing through load two. Let's do a testcase for a specific point in time. Let's say hot 1 for load one is at +60V, and hot two for load two is -60V. Ignoring load two, load one has a current of 1A (60V/60ohms=1A) flowing from hot one through the load and back to the transformer through the neutral. We will call current into the transformer on the neutral positive, and current out of the transformer on the neutral negative. So our neutral has a current of 1A on it for load one. Load two has a current of 1A flowing out of the neutral, through load two, and back into the transformer on hot 2. So, by our signing above, load 2 has a current of -1A on the neutral. To calculate the actual current on the neutral, we add the currents for the two bulbs: 1A + -1A = 0A. Current is flowing out hot one, through bulb one, through bulb two, and back to the transformer on hot 2. Make sense? Now, let's say you have the same setup as above, only load 1 is 30ohms. Well, now the neutral has to carry the extra amp of current. The loads are no longer balanced, so the neutral has to carry the difference. At our 60V test case, the current of load one is now 2A. The neutral current is 2A + -1A = 1A. So, this means that the neutral only carries the difference in power between the two hots. This is also why your neutral doesn't need to be twice as heavy as your hots. Let's say you have 200A service. While you can have 400A of current flowing to 120V appliances all over your home, it is actually +200A to half and -200A to the rest. Your neutral carries 0A, not 400A. Let's go back to our last example, with the 60ohm and 30ohm light bulbs. Let's say some unscroupulous DIYer used the conduit the feed is in for a neutral instead of a dedicated neutral wire. Let's say a clamp to the pipe came off and now we have no neutral connection. Now, we had +60 on hot 1 and -60 on hot 2. So our loads have 120V across them. Now, in this ideal test case, our loads appear as a single 90ohm load to the supply. This means that there is 1.334A flowing through our circuit (120V/90ohms = 1.334A). This also means that load 1 us underpowered by 2/3 of an an amp, while load two is overpowered by one third of an amp. If loads one and two were lightbulbs, bulb one would be dim while bulb two would be brilliant. As both loads have 1.334A flowing through them, load one has 40V across it, while load 2 has 80V across it. Remember, at this point they are both supposed to have 60V across them. Why this is something to worry about Our little set up above is how 240/120V applances work. In, say, your dryer, you would have a third load that is directly across the two hots. Load 3 would be your heater, load 1 would be your timer, and load two could be the light in the drum. If your neutral comes open you could toast your timer or bulb.

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