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<TD><FONT SIZE="2" COLOR="#990000" FACE="Arial, Helvetica"><B>MPEG Layer-3</B></FONT></TD>
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<TD><A HREF="../aac/index.html"><FONT SIZE="2" FACE="Arial, Helvetica"><B>MPEG-2 AAC</B></FONT></A></TD>
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<TD><A HREF="../nmr/index.html"><FONT SIZE="2" FACE="Arial, Helvetica"><B>Measurements</B><BR></FONT></A></TD>
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<TD COLSPAN="2"><FONT SIZE="4" FACE="Arial, Helvetica"><B>MPEG Audio Layer-3</B></FONT></TD>
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<UL>
<LI><A HREF="#1"><FONT FACE="Arial, Helvetica">History</FONT></A>
<LI><A HREF="#3"><FONT FACE="Arial, Helvetica">Sound Quality</FONT></A>
<LI><A HREF="../basics.html"><FONT FACE="Arial, Helvetica">Basics about Perceptual Audio Coding</FONT></A>
<LI><A HREF="layer3faq/index.html"><FONT FACE="Arial, Helvetica">Layer-3 FAQ</FONT></A>
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<TD COLSPAN="2"><A NAME="1"></A><FONT FACE="Arial, Helvetica"><B>History</B></FONT></TD>
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<TD COLSPAN="3" HEIGHT="30"> </TD>
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<TD><IMG SRC="fhg_tran.gif" WIDTH="30" HEIGHT="1" ALIGN="BOTTOM" BORDER="0"></TD>
<TD><FONT FACE="Arial, Helvetica">In 1987, the IIS started to work on perceptual audio coding in the framework of the
EUREKA project EU147, Digital Audio Broadcasting (DAB). In a joint cooperation with the University of Erlangen
(Prof. Dieter Seitzer), the IIS finally devised a very powerful algorithm that is standardized as ISO-MPEG Audio
Layer-3 (IS 11172-3 and IS 13818-3).</FONT></TD>
<TD> </TD>
</TR>
<TR>
<TD> </TD>
<TD><FONT FACE="Arial, Helvetica"><B>Without data reduction</B>, digital audio signals typically consist of 16 bit
samples recorded at a sampling rate more than twice the actual audio bandwidth (e.g. 44.1 kHz for Compact Disks).
So you end up with more than <B>1.400 Mbit</B> to represent just <B>one second of stereo music in CD quality</B>.
By using MPEG audio coding, you may shrink down the original sound data from a CD by a factor of 12, without losing
sound quality. Factors of 24 and even more still maintain a sound quality that is significantly better than what
you get by just reducing the sampling rate and the resolution of your samples. Basically, this is realized by <I>perceptual
coding</I> techniques addressing the perception of sound waves by the human ear.</FONT></TD>
<TD> </TD>
</TR>
<TR>
<TD> </TD>
<TD>
<P><FONT FACE="Arial, Helvetica">Using MPEG audio, one may achieve a typical data reduction of</FONT></P>
<CENTER>
<P>
<TABLE BORDER="1" CELLPADDING="3">
<TR>
<TD ALIGN="CENTER" BGCOLOR="#C0C0C0">
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica"><B>1:4</B></FONT>
</TD>
<TD><FONT FACE="Arial, Helvetica">by <B>Layer 1</B> (corresponds with 384 kbps for a stereo signal),</FONT></TD>
</TR>
<TR>
<TD ALIGN="CENTER" BGCOLOR="#C0C0C0">
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica"><B>1:6...1:8</B></FONT>
</TD>
<TD><FONT FACE="Arial, Helvetica">by <B>Layer 2</B> (corresponds with 256..192 kbps for a stereo signal),</FONT></TD>
</TR>
<TR>
<TD ALIGN="CENTER" BGCOLOR="#C0C0C0">
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica"><B>1:10...1:12</B></FONT>
</TD>
<TD><FONT FACE="Arial, Helvetica">by <B>Layer 3</B> (corresponds with 128..112 kbps for a stereo signal),</FONT></TD>
</TR>
</TABLE></P></CENTER>
<P><FONT FACE="Arial, Helvetica">still maintaining the original CD sound quality.</FONT>
</TD>
<TD> </TD>
</TR>
<TR>
<TD> </TD>
<TD><FONT FACE="Arial, Helvetica">By exploiting stereo effects and by limiting the audio bandwidth, the coding schemes
may achieve an acceptable sound quality at even lower bitrates. MPEG Layer-3 is the most powerful member of the MPEG
audio coding family. For a given sound quality level, it requires the lowest bitrate - or for a given bitrate,
it achieves the highest sound quality.</FONT></TD>
<TD> </TD>
</TR>
<TR>
<TD COLSPAN="3" HEIGHT="30"> </TD>
</TR>
<TR>
<TD COLSPAN="3"><A NAME="3"></A><FONT FACE="Arial, Helvetica"><B>Sound Quality</B></FONT></TD>
<TD> </TD>
</TR>
<TR>
<TD COLSPAN="3" HEIGHT="30"> </TD>
</TR>
<TR>
<TD> </TD>
<TD>
<P><FONT FACE="Arial, Helvetica">Some typical performance data of <B>MPEG Layer-3</B> are:</FONT></P>
<CENTER>
<P>
<TABLE BORDER="2" CELLPADDING="3">
<TR>
<TH BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">sound quality</FONT></TH>
<TH BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">bandwidth</FONT></TH>
<TH BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">mode</FONT></TH>
<TH BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">bitrate</FONT></TH>
<TH BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">reduction ratio</FONT></TH>
</TR>
<TR ALIGN="CENTER">
<TD ALIGN="LEFT" BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">telephone sound</FONT></TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">2.5 kHz</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">mono</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">8 kbps *</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">96:1</FONT>
</TD>
</TR>
<TR ALIGN="CENTER">
<TD ALIGN="LEFT" BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">better than shortwave</FONT></TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">4.5 kHz</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">mono</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">16 kbps</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">48:1</FONT>
</TD>
</TR>
<TR ALIGN="CENTER">
<TD ALIGN="LEFT" BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">better than AM radio</FONT></TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">7.5 kHz</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">mono</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">32 kbps</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">24:1</FONT>
</TD>
</TR>
<TR ALIGN="CENTER">
<TD ALIGN="LEFT" BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">similar to FM radio</FONT></TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">11 kHz</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">stereo</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">56...64 kbps</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">26...24:1</FONT>
</TD>
</TR>
<TR ALIGN="CENTER">
<TD ALIGN="LEFT" BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">near-CD</FONT></TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">15 kHz</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">stereo</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">96 kbps</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">16:1</FONT>
</TD>
</TR>
<TR ALIGN="CENTER">
<TD ALIGN="LEFT" BGCOLOR="#C0C0C0"><FONT FACE="Arial, Helvetica">CD</FONT></TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">>15 kHz</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">stereo</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">112..128kbps</FONT>
</TD>
<TD>
<P ALIGN="CENTER"><FONT FACE="Arial, Helvetica">14..12:1</FONT>
</TD>
</TR>
<TR>
<TD COLSPAN="5"><FONT SIZE="2" FACE="Arial, Helvetica">*) Fraunhofer uses a non-ISO extension of MPEG Layer-3 for enhanced performance
("MPEG 2.5")</FONT></TD>
</TR>
</TABLE></CENTER>
</TD>
<TD> </TD>
</TR>
<TR>
<TD> </TD>
<TD><FONT FACE="Arial, Helvetica">In all international listening tests, MPEG Layer-3 impressively proved its superior performance,
maintaining the original sound quality at a data reduction of 1:12 (around 64 kbit/s per audio channel). If applications
may tolerate a limited bandwidth of around 10 kHz, a reasonable sound quality for stereo signals can be achieved
even at a reduction of 1:24.</FONT></TD>
<TD> </TD>
</TR>
<TR>
<TD> </TD>
<TD><FONT FACE="Arial, Helvetica">For the use of low bit-rate audio coding schemes in broadcast applications at bitrates
of 60 kbit/s per audio channel, the ITU-R recommends MPEG Layer-3. (ITU-R doc. BS.1115)</FONT></TD>
<TD> </TD>
</TR>
<TR>
<TD COLSPAN="3" HEIGHT="30"> </TD>
</TR>
<TR>
<TD COLSPAN="2">
<FONT FACE="Arial, Helvetica"><B>MPEG Audio Layer-3 - Frequently Asked Questions</B></FONT></TD>
<TD> </TD>
</TR>
<TR>
<TD> </TD>
<TD><FONT FACE="Arial, Helvetica">Fore more information take a look at our <A HREF="layer3faq/index.html"><B>Layer-3 FAQ</B></A>.</FONT>
<P><CENTER><A HREF="#top"><FONT SIZE="2">| TOP |</FONT></A></CENTER>
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<FONT SIZE="2" FACE="arial, helvetica"><I><B>Copyright ©1998
<A HREF="http://www.fhg.de/contact.html">Fraunhofer-Gesellschaft</A></B></I></FONT>
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