M4A files are a type of audio file developed and popularised by Apple. Since 2007, music purchased through the iTunes store has been in m4a format, therefore accounting for over 15 billions files worldwide. MP4 and M4A files are often confused, and the two are quite similar, being both based on the MPEG-4 codec. However, M4A is a file comprising solely of audio, whereas MP4 may also contain video.
M4A files are superior to MP3 in terms of the scale of compression and audio quality. The M4A file uses Apple's codec and resides within the MPEG-4 container. The main benefit of M4A is that files are compressed but are lossless. This means they can be decoded back to the original quality they were at the point of compression. Another benefit of M4A files are that do not carry any Digital Rights Management (DRM) protection associated with other files meaning they are less restricted.
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AAC is similar to MP3. It essentially cuts out, or compresses, information that the human ear cannot pick up thereby making digital files smaller and more easily managed and therefore quicker to download. AAC is about half the size of MP3 but with better quality. It is at least one tenth the size of CD digital data. Apple are the biggest users of this format and if you have an iPod or iPhone then you will have come across this format as it is iTunes default audio format.
AAC is similar in concept to MP3 but goes further. It too compresses digital audio files but to a bigger degree. It is also part of the MPEG-4 standard, it is most widely used to create small digital audio files. The current variant is specified in ISO/IEC standard 14496-3. Like MP3, AAC is a lossy algorithm. The human hearing system cannot hear quiet sounds in the presence of loud sounds of a similar frequency; for example, a voice conversation cannot be heard while an aeroplane flies low overhead. This is known as auditory masking, this allows the discarding of data with minimal loss of quality.
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