Posted by fred-bloggs on 04/12/06 13:13

"Michael Andreas" <andy@dachrinne.de> wrote in
news:e1iplo$9u4$1@online.de:

> Hi,
>
> I know MPEG 2.5 is an unofficial extension of MPEG 2
> to support even lower sampling rates.
>
> My audiofile:
> MPEC 2.5 Layer 3, 8000Hz, 16KBps, Mono
> plays a hall at the background.
>
> Now I read at the help of my tool:
> MPEG Version 2.5 was added lately to the MPEG 2 standard. It is an
> extension used for very low bitrate files, allowing the use of lower
> sampling frequencies. If your decoder does not support this extension,
> it is recommended for you to use 12 bits for synchronization instead
> of 11 bits.
>
> My question:
>
> What means synchronisation 12 bits instead of 12 bits?
>

An mp3 stream is split into frames which vary in duration with sample
rate (for example 26 milliseconds at 44.1 khz). At the start of each
frame is a 32 bit frame header which contains information such as sample
rate, bit rate and mode. The first 12 bits of the header are set to 1 and
are called the frame sync. Mpeg 2.5 uses only 11 bits and therefore
breaks the mpeg 1&2 standards.

If your mp3 player cannot cope with mpeg2.5, resample your mp3s to 16kHz.


--
fred

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