Explain at least two techniques used by codecs to compress sound data.?
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There is by definition, two ways to compress any type of data:\n1. Lossy\n2. Lossless\n\nMost sound compression algorithms use lossy compression to compress the sound data.  It is reasonable to achieve 10x compression with little noticable loss of sound quality using a popular compression method such as MP3 or the more recent MP4 (which are actually both substandards of the MPEG specifications, for use in compressing video (moving picture) data).  The MPEG specs use a psycho-acoustic modelling technique in order to remove parts of the sound that are not noticable based on the limitations of human hearing.  For example, in a loud passage, a soft background sound will not be heard clearly and thus can be encoded using less bits.  There are also various ways of doing the encoding, using a fixed bit bucket (known as constant bit rate) or using a variable bit bucket, where bits can be traded based on time so that passages that are tougher to encode can use more bits (variable bit rate).\n\nLossless compression techniques generally fall under the same category as general compression algorithms such as those used for zipping files, etc.  However, sound does have certain characteristics that when exploited will allow better compression than a standard zipping of the PCM data would allow.  A good explanation of this type of technique can be found on the website linked below.  Because of the inherent randomness in sound data, typical lossless compression rates are about 2X.
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Once you have reduced the quality of the file, you have permanently reduced the quality of the song. You could up mix back to 128kbps but it would sound just like the 64kbps.
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MPEG-4 Part 14 or *.mp4, is a file format (a so called container) specified as a part of the ISO/IEC MPEG-4 international standard. It is used to store media types defined by the ISO/IEC Moving Picture Experts Group, and can be used to store other media types as well. It is, or will be, typically used to store data in files, though it will be used in data streams and possibly in other ways. \n\nMP3 is an acronym for MPEG-1 or MPEG-2 audio layer 3. MP3 is the file extension for MPEGaudio layer 3. Layer 3 is one of three coding schemes (layer 1, layer 2 and layer 3) for the compression of audio signals. Layer 3 uses perceptual audio coding and psychoacoustic compression to remove all superfluous information (more specifically, the redundant and irrelevant parts of a sound signal. The stuff the human ear doesn't hear anyway).
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You can use different programs to convert the sound file. One I have found that works well is Goldwave. However, the trial version only allows so many conversions before you have to buy the program.
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there are a lot of compressing tools available in the internet. winzip, winrar, winace, etc all can compress files effectively.
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Divx with the required codecs is very good.\n\nhttp://www.divx.com
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You simply need the correct codecs (COmpressors and DECompressors) installed to play the files.\n\nThe one I use is called K-Lite Codec Pack, and is free.\n\nYou can download it from here: http://www.free-codecs.com/download/K_Lite_Codec_Pack.htm
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the quality isn't so much in the format but in the bitrate.  when you are ripping music, change the bit rate or quality to 320 instead of the standard 128
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http://www.divx.com/divx/\n\nIs probably best for codecs.
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Audio files are normally compressed and reduced file size by audio compressor software before distributing it. When you are going to play an compress audio file you need a decompressor software to retain its original value. This type of decompressor software called codec. It's very essential to play a compressed audio file format like .mp3, .ram, .au etc
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You could recompress it with a different codec and/or data rate.  VirtualDub is good , free, and easy to use.\n\nhttp://www.virtualdub.org/
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wav, te reason: mp3 is compressed audio and how mp3 is compressed is by stripping some of the frequincies you "cant hear", but on a proper system or set of monitors tyou will def hear the difference between a wav and mp3.\n\nwav isnt comressed and therefore the best medium to work in  ;)
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I use a program called\nKeep in mind that reencoding audio from one format to another may result in quality loss.\n\nBy searching versiontracker.com, I found a few programs, such as the freeware called 'Ogg Drop.'
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I have always like the K Lite codec pack. See link below. What you need is dependent on what you are trying to play and how it was encoded though.
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From a software developer point of view. This will be really hard to do and come up with a algorithm for seperating human voices from the regular music. They are sampled in digital files and to find which wave is the vioice is too hard for a computer to tell apart.
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Compress them using winzip or winrar or a imilar program
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For what purpose? There are both audio and video codecs. Some are excellent for compression, some are excellent for quality. Some are excellent for compatibility with devices and different types of computers.\n\nFor audio codecs, I like mp3 (VBR) for general purpose and compatibility, and ogg for maximum compression with good quality.\n\nFor video codecs, MPEG-4 is a great standard, with Apple's H.264 codec being awesome for web streaming. For minimizing long videos to fit in limited space, the new XviD codec works very well and is free.