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Music Studio Technology
Audio Compression Codecs
The original digital audio files were large and video files were much larger. File compression involves hardware and/or software that reduces the file size. Compression requires compromises between storage space requirements, quality of reproduction and the cost of the hardware/software required to decompress in a reasonable time. A variety of compression strategies have been used; two groups are recognized – the loss and that lossless referring to the acoustic information content of the file. Loss methods eliminate portions of the acoustic information based on psychoacoustic studies that revealed that some sound information was not perceived by the listener.
The software/hardware used to compress and decompress is a codec. Digital audio as wave files can be compressed to MP3, Window's WMA files or Apple's AIFF. The MPEG-1 codec is used for Video CDs and online video. This is most universal codec for video players. DVD movies are compressed with a higher quality MPEG-2 codec.
The audio CD standard is a wav file sample rate of 44.1 kHz, a bit depth of 16 which runs at 1,411.2 k bits per second. A DVD standard has a file sample rate of 48 kHz, a bit depth of 24. The MPEG Advanced Audio Coding (AAC or MPEG-2) can use higher sampling frequencies ( 96kHz).Listening tests demonstrated that AAC produces slightly better stereo audio quality at 96 kb/s than MP3 at 128 kb/s.
MP3 compression codecs changed the music industry simply because they reduced the size of audio files while retaining reasonable sound quality. The smaller audio files could be stored more efficiently in the memories built into portable music players and Smartphone's. MP3 files were quicker to download from internet sound libraries and music delivery from online sources threatened other methods of music distribution. By 1997, the website mp3.com offered thousands of MP3s created by independent artists for free. Peer-to-peer file sharing of music ripped from CDs and converted to MP3 became popular.
We use three MP3 compression targets expressed as Kbits per second : 128, 192 and 320. The MP3 files are used for downloads and online music players. Our approach to presenting music online now favors streaming.