This is done to limit the temporal spread of quantization noise accompanying the transient. If there is a transient 192 samples are taken instead of 576. During encoding 576 time domain samples are taken and are transformed to 576 frequency domain samples. Implementers of the standard were supposed to devise their own algorithms suitable for removing parts of the information in the raw audio (or rather its MDCT representation in the frequency domain). The decoding algorithm and file format, as a contrast, are well defined. The MPEG-1 standard does not include a precise specification for an MP3 encoder. It supports multichannel files (see page), sampling rates from 16 kHz to 24 kHz (MPEG2 Layer 3) and 32 kHz to 48 kHz (MPEG1 Layer 3)įormal and informal listening tests have shown that MP3 at the 160-224 kbps range provide encoded results indistinguishable from the original materials in most of the cases.Įncoding and decoding Encoding of MP3 audio (486 DX2-100 is enough for real-time decoding) It soon became the de facto standard for lossy audio encoding, due to the high compression rates (1/11 of the original size, still retaining considerable quality), the high availability of decoders and the low CPU requirements for playback. It is standardized as ISO-MPEG Audio Layer-3 (IS 11172-3 and IS 13818-3). The MP3 algorithm development started in 1987, with a joint cooperation of Fraunhofer IIS-A and the University of Erlangen.
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