MPEG-1 Audio Layer I explained

MPEG-1 Audio Layer I, commonly abbreviated to MP1, is one of three audio formats included in the MPEG-1 standard. It is a deliberately simplified version of MPEG-1 Audio Layer II (MP2), created for applications where lower compression efficiency could be tolerated in return for a less complex algorithm that could be executed with simpler hardware requirements. While supported by most media players, the codec is considered largely obsolete, and replaced by MP2 or MP3.

For files only containing MP1 audio, the file extension .mp1 is used.

A limited version of MPEG-1 layer I was also used by the Digital Compact Cassette format, in the form of the PASC (Precision Adaptive Subband Coding) audio compression codec. The bit rate of PASC was fixed at 384 kilobits per second, and when encoding audio at a sample frequency of 44.1 kHz, PASC regards the padding slots as 'dummy'^[4] and sets them to zero, whereas the ISO/IEC 11172-3 standard uses them to store data.

Specification

MPEG-1 Layer I is defined in ISO/IEC 11172-3, the first version of which was published in 1993.

• Sampling rates: 32, 44.1 and 48 kHz
• Bitrates: 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416 and 448 kbit/s^[5]

An extension has been provided in MPEG-2 Layer I and is defined in ISO/IEC 13818-3, which first version was published in 1995.

• Additional sampling rates: 16, 22.05 and 24 kHz
• Additional bitrates: 48, 56, 80, 112, 144 and 176 kbit/s

MP1 uses a comparatively simple sub-band coding, using 32 sub-bands.^[6]

External links

• • Sub-Band Coding: A description of sub-band coding, including an overview of the MP1 codec.

Notes and References

1. Book: Patel K, Smith BC, Rowe LA . Proceedings of the first ACM international conference on Multimedia - MULTIMEDIA '93 . Performance of a software MPEG video decoder . 1993-09-01 . https://dl.acm.org/doi/10.1145/166266.166274 . ACM Multimedia . New York City . Association for Computing Machinery . 75–82 . 10.1145/166266.166274 . 978-0-89791-596-0. 3773268 . Reference 3 in the paper is to Committee Draft of Standard ISO/IEC 11172, December 6, 1991.
2. Web site: ISO/IEC 11172-3:1993 - Information technology -- Coding of moving pictures and associated audio for digital storage media at up to about 1.5 Mbit/s -- Part 3: Audio . ISO . 1993 . 2010-07-14.
3. Web site: ISO/IEC 13818-3:1995 - Information technology -- Generic coding of moving pictures and associated audio information -- Part 3: Audio . ISO . 1995 . 2010-07-14.
4. Web site: Philips DCC System Description Draft . Archive.org . September 1994 . Philips Consumer Electronics B.V. . 14 April 2021 . The padding bit [...] indicates whether the current frame has a 'dummy' slot.
5. Web site: MPEG Audio Frame Header. 2003-08-03. 2009-05-29. dead. https://web.archive.org/web/20150208104604/http://www.mpgedit.org/mpgedit/mpeg_format/mpeghdr.htm. 2015-02-08.
6. Web site: MPEG-1 audio layer 1. TheFreeDictionary.com.