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You don't normally have any option about the you need to use but this piece explains why there are so many formats and why they keep changing. There are too many formats for storing, digital audio information! They all try to capture the waveform of the original sound but that is the easy part. The different formats emerge as they try to save space. This is where it gets complex. Why so many formats?To economise on the amount of digital space required, the formats accept that human hearing at its very best works in the 20Hz to 20kHz range of frequencies and not everyone can hear even these frequencies. Few rooms and absolutely no headphones can deliver the low frequencies (the 20Hz end). Good speakers, for example, can output about 60Hz-16kHz. And the low frequencies turn up in unwanted places as they 'seek out' roof spaces where they can express themselves. MP3 files remove some of the frequencies to save storage space. ACC takes account of the physiology of human hearing and has a more complex set of filtering rules to trim the range stored. AAC is a 'perceptual audio codec' which means that it discards information that is deemed less important to the hearing quality. After the formats have trimmed some frequencies, there is the sampling rate. Ironically, it was the old analogue records that had the whole recorded sound (more or less). Whereas, in the digital world, you are only getting samples of the original sound. But before you rush and ask for your money back on all of the CDs you have purchased, you need to know just how fast the sampling is. CD quality uses a 128kbps/44.1kHz sample rate which is about three times faster than the 'highest' note the normal ear can hear. Just as you do not notice the flicker at the cinema when the individual frames are displayed, you won't notice the gaps. MP3 goes for a 64kbps/32kHz sample rate. ACC uses 128kbps/96kHz sample rate which looks better at first but it removes some frequencies and also has a variable bit-rate (VBR). And MP3 has also provided a VBR version and as processing power increases so the amount of complex processing will doubtless increase and other formats will emerge. So you can't judge an audio format just by looking at the sample rate because modern formats exploit the greater processing power available to save space by processing the signal. The proliferation of formats is therefore a consequence of the many different solutions that exist to address the quality-v-size issue. So how do you choose?In the real world, the two key issues are compatibility and 'what does it sound like?' Most of the formats are designed to meet some specific requirements. In a world dominated by ITunes and IPod, the MP3 and AAC formats dominate. MP3 wins the compatibility competition. AAC sounds better than MP3 but not quite CD quality. (There are many others listed below often used on proprietary or specialist equipment.) Machines like the iPod support both of these popular formats.
How much space? AIFF and WAV. files need about 10 MEGs per minute of music. MP3 and AAC take around 1MEG per minute. |
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